Lanqun Mao

We report here a new electrochemical method for in situ deposition of Pt nanoparticles onto multiwalled carbon nanotubes (MWNTs) to form a three-dimensional uniform Pt/MWNT nanocomposite with excellent electrocatalytic activity toward the oxidation of methanol, by taking advantage of the good solubility of MWNTs and chloroplatinic acid (H2PtCl6) into ionic liquids (i.e., BmimPF6) to form a homogeneous and electronic conductive gel matrix. The gel is prepared by first dissolving H2PtCl6 into ionic liquids and then grinding the ionic liquids with MWNTs. The formation of the nanocomposite is accomplished by the reduction of the H2PtCl6 precursor onto MWNTs, both in the gel matrix. Scanning electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry results reveal that the good homogeneity and conductivity of the prepared gel matrix substantially results in the formation of a three-dimensional nanocomposite, in which Pt nanoparticles are homogeneously deposited onto MWNTs in the gel matrix. Voltammetric study with the as-prepared Pt/MWNT nanocomposite indicates that the nanocomposite processes an enhanced electrocatalytic activity toward the oxidation of methanol, as compared with the Pt/MWNT nanocomposite prepared with the conventional electrochemical method by the reduction of the H2PtCl6 precursor in the solution phase onto MWNTs confined onto conducting substrate. The strategy demonstrated here is facile, cost-effective, and environmentally benign and may be versatile for the preparation of three-dimensional MWNT-based nanocomposites with other kinds of metal nanoparticles with excellent properties.

Graphdiyne as Electrode Material: Tuning Electronic State and Surface Chemistry for Improved Electrode Reactivity

Co-reporter:Shuyue Guo, Hailong Yan, Fei Wu, Lijun Zhao, Ping Yu, Huibiao Liu, Yuliang Li, and Lanqun Mao

Analytical Chemistry December 5, 2017 Volume 89(Issue 23) pp:13008-13008

Publication Date(Web):November 10, 2017

DOI:10.1021/acs.analchem.7b04115

Graphdiyne (GDY) is recently synthesized two-dimensional carbon allotrope with hexagonal rings cross-linked by diacetylene through introducing butadiyne linkages (−C≡C–C≡C−) to form 18-C hexagons and is emerging to be fundamentally interesting and particularly useful in various research fields. In this study, we for the first time find that GDY can be used as an electrode material with reactivity tunable by electronic states and surface chemistry of GDY. To demonstrate this, GDY is oxidized into graphdiyne oxide (GDYO) that is then chemically and electrochemically reduced into chemically reduced GDYO (cr-GDYO) and electrochemically reduced GDYO (er-GDYO), respectively. Electrode reactivity of GDY and its derivatives (i.e., GDYO, cr-GDYO, and er-GDYO) is studied with hexaammineruthenium chloride ([Ru(NH3)6]Cl3) and potassium ferricyanide (K3Fe(CN)6) as redox probes. We find that electron transfer kinetics of the redox probes employed here at GDYs depends on the density of electronic state (DOS) and the synergetic effects of the surface chemistry as well as the hydrophilicity of the materials, and that the electron transfer kinetics at cr-GDYO and er-GDYO are faster than those at GDY and GDYO, and quite comparable with those at carbon nanotubes and graphene and its derivatives (i.e., GO, cr-GO, and er-GO). These properties, combined with the unique electronic and chemical structures of GDY, essentially enable GDY as a new kind of electrode material for fundamental studies on carbon electrochemistry and various electroanalytical applications.

Mitochondria Targeted Nanoscale Zeolitic Imidazole Framework-90 for ATP Imaging in Live Cells

Co-reporter:Jingjing Deng, Kai Wang, Ming Wang, Ping Yu, and Lanqun Mao

Journal of the American Chemical Society April 26, 2017 Volume 139(Issue 16) pp:5877-5877

Publication Date(Web):April 7, 2017

DOI:10.1021/jacs.7b01229

Zeolitic imidazole frameworks (ZIFs) are an emerging class of functional porous materials with promising biomedical applications such as molecular sensing and intracellular drug delivery. We report herein the first example of using nanoscale ZIFs (i.e., ZIF-90), self-assembled from Zn2+ and imidazole-2-carboxyaldehyde, to target subcellular mitochondria and image dynamics of mitochondrial ATP in live cells. Encapsulation of fluorescent Rhodamine B (RhB) into ZIF-90 suppresses the emission of RhB, while the competitive coordination between ATP and the metal node of ZIF-90 dissembles ZIFs, resulting in the release of RhB for ATP sensing. With this method, we are able to image mitochondrial ATP in live cells and study the ATP level fluctuation in cellular glycolysis and apoptosis processes. The strategy reported here could be further extended to tune nanoscale ZIFs inside live cells for targeted delivery of therapeutics to subcellular organelles for advanced biomedical applications.

Role of Organic Solvents in Immobilizing Fungus Laccase on Single-Walled Carbon Nanotubes for Improved Current Response in Direct Bioelectrocatalysis

Co-reporter:Fei Wu, Lei Su, Ping Yu, and Lanqun Mao

Journal of the American Chemical Society 2017 Volume 139(Issue 4) pp:1565-1574

Publication Date(Web):January 4, 2017

DOI:10.1021/jacs.6b11469

Improving bioelectrocatalytic current response of redox enzymes on electrodes has been a focus in the development of enzymatic biosensors and biofuel cells. Herein a mediatorless electroreduction of oxygen is effectively improved in terms of a remarkable enhancement by ca. 600% in maximum reductive current by simply adding 20% ethanol into laccase solution during its immobilization onto single-walled carbon nanotubes (SWCNTs). Conformation analysis by circular dichroism and attenuated total reflectance infrared spectroscopy demonstrate promoted laccase-SWCNTs contact by ethanol, thus leading to favorable enzyme orientation on SWCNTs. Extended investigation on acetone-, acetonitrile-, N,N-dimethylformamide (DMF)-, or dimethyl sulfoxide (DMSO)-treated laccase-SWCNTs electrodes shows a 400% and 350% current enhancement at maxima upon acetone and acetonitrile treatment, respectively, and a complete diminish of reductive current by DMF and DMSO. These results together reveal the important role of organic solvents in regulating laccase immobilization for direct bioelectrocatalysis by balancing surface wetting and protein denaturing.

In Vivo Analysis with Electrochemical Sensors and Biosensors

Co-reporter:Tongfang Xiao, Fei Wu, Jie Hao, Meining Zhang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2017 Volume 89(Issue 1) pp:

Publication Date(Web):November 7, 2016

DOI:10.1021/acs.analchem.6b04308

Ultrathin Cell-Membrane-Mimic Phosphorylcholine Polymer Film Coating Enables Large Improvements for In Vivo Electrochemical Detection

Co-reporter:Xiaomeng Liu;Tongfang Xiao;Dr. Fei Wu;Mo-Yuan Shen;Assoc. Dr. Meining Zhang; Hsiao-hua Yu; Lanqun Mao

Angewandte Chemie 2017 Volume 129(Issue 39) pp:11964-11968

Publication Date(Web):2017/09/18

DOI:10.1002/ange.201705900

AbstractResisting biomolecule adsorption onto the surface of brain-implanted microelectrodes is a key issue for in vivo monitoring of neurochemicals. Herein, we demonstrate that an ultrathin cell-membrane-mimic film of ethylenedioxythiophene tailored with zwitterionic phosphorylcholine (EDOT-PC) electropolymerized onto the surface of a carbon fiber microelectrode (CFE) not only resists protein adsorption but also maintains the sensitivity and time response for in vivo monitoring of dopamine (DA). As a consequence, the as-prepared PEDOT-PC/CFEs could be used as a new reliable platform for tracking DA in vivo and would help understand the physiological and pathological functions of DA.

Ultrathin Cell-Membrane-Mimic Phosphorylcholine Polymer Film Coating Enables Large Improvements for In Vivo Electrochemical Detection

Co-reporter:Xiaomeng Liu;Tongfang Xiao;Dr. Fei Wu;Mo-Yuan Shen;Assoc. Dr. Meining Zhang; Hsiao-hua Yu; Lanqun Mao

Angewandte Chemie International Edition 2017 Volume 56(Issue 39) pp:11802-11806

Publication Date(Web):2017/09/18

DOI:10.1002/anie.201705900

Self-powered electrochemical systems as neurochemical sensors: toward self-triggered in vivo analysis of brain chemistry

Co-reporter:Fei Wu;Ping Yu

Chemical Society Reviews 2017 vol. 46(Issue 10) pp:2692-2704

Publication Date(Web):2017/05/22

DOI:10.1039/C7CS00148G

Real-time in vivo analysis of neurochemical dynamics has great physiological and pathological implications for a full understanding of the brain. Self-powered electrochemical systems (SPESs) built on galvanic cell configurations bear the advantages of easy miniaturization for implantation and no interference to electric activities of neurons over traditional externally-powered electrochemical sensors for self-triggered in vivo analysis. However, this is still a new concept for in vivo neurochemical sensing with few implanted examples reported so far. This tutorial review summarizes the development of SPESs toward implantable applications from both principal and practical perspectives, ultimately aimed at providing a guide map to the future design of neurochemical sensors for in vivo analysis of brain chemistry.

Bioelectrochemistry for in vivo analysis: Interface engineering toward implantable electrochemical biosensors

Co-reporter:Fei Wu, Ping Yu, Lanqun Mao

Current Opinion in Electrochemistry 2017 Volume 5, Issue 1(Volume 5, Issue 1) pp:

Publication Date(Web):1 October 2017

DOI:10.1016/j.coelec.2017.08.008

•Key issues in bioelectrochemistry for in vivo analysis are discussed.•Immobilized mediators are preferred for implantable enzymatic biosensors.•Direct bioelectrocatalysis simplifies bioelectrode construction.•Implantable enzymatic biosensors must be oxygen and environment tolerant.•Self-powered enzymatic biosensors are the future direction for in vivo analysis.With a long history in research, bioelectrochemistry has emerged as a hot spot in the development of implantable biosensors with desired selectivity, sensitivity and spatiotemporal resolution for accurate analysis of electroinactive species in vivo. To catalyze electrode reactions (oxidation or reduction) of target analytes, enzymes are employed as the efficient bioelectrocatalysts immobilized on the electrodes. In bioelectrochemistry, the biggest challenge is the interfacial electron transfer between the redox active centers of enzymes and electrode surfaces. Besides, enzymatic electrodes are prone to inhibition and inactivation by environmental factors (co-substrates, inhibitors, pH, etc.). Rational design of the electrode surface/interface is necessitated to fulfill the requirements of in vivo applications. This mini review covers the recent and representative progress on interface engineering to enable bioelectrochemistry for in vivo analysis with an emphasis on heterogeneous electron transfer, oxygen dependence and microenvironment tolerance of bioelectrodes and self-powered electrochemical biosensors as well.

Paraflocculus plays a role in salicylate-induced tinnitus

Co-reporter:Yali Du, Junxiu Liu, Qin Jiang, Qingchuan Duan, Lanqun Mao, Furong Ma

Hearing Research 2017 Volume 353(Volume 353) pp:

Publication Date(Web):1 September 2017

DOI:10.1016/j.heares.2017.06.013

•Salicylate injection increased spontaneous firing rates in paraflocculus.•Electric stimulation changed neural firing in auditory cortex.•Extracellular glutamic acid was significantly increased by salicylate.Tinnitus impairs quality of life of about 1–2% of the whole population. In most severe situation, tinnitus may cause social isolation, depression and suicide. Drug treatments for tinnitus are generally ineffective, and the mechanisms of tinnitus are still undetermined. Accumulating evidence suggests that tinnitus is related to changes of widespread brain networks. Recent studies propose that paraflocculus (PFL), which is indirectly connected to various cortical regions, may be a gating zone of tinnitus. So we examined the electrophysiological changes and neurotransmitter alterations of the PFL in a rat model of sodium salicylate (SS)-induced tinnitus. We found that spontaneous firing rate (SFR) of the putative excitatory interneurons of the PFL was significantly increased. The level of glutamic acid, which is the main excitatory neurotransmitter in the nervous system, was also dramatically increased in the PFL after SS treatment. These results confirmed the hyperactivity of PFL in the rats with SS-treatment, which might be due to the increased glutamic acid. Then we examined the SFR of the auditory cortex (AC), the center for auditory perception, before and after electrical stimulation of the PFL. 71.4% (105/147) of the recorded neurons showed a response to the stimulation of the PFL. The result demonstrated that stimulation of the PFL could modulate the activity of the AC. Our study suggests a role of PFL in SS-induced tinnitus and AC as a potential target of PFL in the process of tinnitus.

Size-Controlled Synthesis of Porphyrinic Metal–Organic Framework and Functionalization for Targeted Photodynamic Therapy

Co-reporter:Jihye Park; Qin Jiang; Dawei Feng; Lanqun Mao;Hong-Cai Zhou

Journal of the American Chemical Society 2016 Volume 138(Issue 10) pp:3518-3525

Publication Date(Web):February 19, 2016

DOI:10.1021/jacs.6b00007

The understanding of nanomaterials for targeted cancer therapy is of great importance as physical parameters of nanomaterials have been shown to be strong determinants that can promote cellular responses. However, there have been rare platforms that can vastly tune the core of nanoparticles at a molecular level despite various nanomaterials employed in such studies. Here we show targeted photodynamic therapy (PDT) with Zr(IV)-based porphyrinic metal–organic framework (MOF) nanoparticles. Through a bottom-up approach, the size of MOF nanoparticles was precisely tuned in a broad range with a designed functional motif, built upon selection of building blocks of the MOF. In particular, molecular properties of the porphyrinic linker are maintained in the MOF nanoparticles regardless of their sizes. Therefore, size-dependent cellular uptake and ensuing PDT allowed for screening of the optimal size of MOF nanoparticles for PDT while MOF nanoparticle formulation of the photosensitizer showed better PDT efficacy than that of its small molecule. Additionally, Zr6 clusters in the MOF enabled an active targeting modality through postsynthetic modification, giving even more enhanced PDT efficacy. Together with our finding of size controllability covering a broad range in the nano regime, we envision that MOFs can be a promising nanoplatform by adopting advanced small molecule systems into the tunable framework with room for postsynthetic modification.

Graphdiyne oxide as a platform for fluorescence sensing

Co-reporter:Chunxia Wang, Ping Yu, Shuyue Guo, Lanqun Mao, Huibiao Liu and Yuliang Li

Chemical Communications 2016 vol. 52(Issue 32) pp:5629-5632

Publication Date(Web):22 Mar 2016

DOI:10.1039/C6CC01856D

Graphdiyne (GD), a new kind of two-dimensional carbon allotrope consisting of a hexagonal ring and a diacetylenic linkage unit, is observed to exhibit a high fluorescence quenching ability and can be used as a new platform for fluorescence sensing, where GD oxide, the oxidized form of GD, is found to exhibit higher quenching ability than GD. As a proof-of-concept demonstration, GD oxide is used to establish a new platform for effective fluorescence sensing of DNA and thrombin with a high sensitivity and selectivity.

Synergistic Coordination and Hydrogen Bonding Interaction Modulate the Emission of Iridium Complex for Highly Sensitive Glutamine Imaging in Live Cells

Co-reporter:Qin Jiang, Ming Wang, Lifen Yang, Hui Chen, and Lanqun Mao

Analytical Chemistry 2016 Volume 88(Issue 20) pp:10322

Publication Date(Web):September 30, 2016

DOI:10.1021/acs.analchem.6b03383

Highly selective detection of intracellular glutamine (Gln) is very essential to understand the roles of Gln in some biological processes. Here, we report a new fluorescent method for selective imaging of Gln in live cells with an aldehyde-containing iridium complex, [Ir(pba)2(DMSO)2]PF6 (Hpba = 4-(2-pyridiyl)benzaldehyde) (Ir1), as the probe. Density functional theory (DFT) calculation and experimental results suggest that the coordination and hydrogen bonding interaction between Ir1 and Gln synergistically stabilize the Ir1–Gln complex, modulate charge-transfer characteristics and emission of Ir1, and as a consequence, enable Ir1 as the probe for the fluorescent sensing of Gln. The sensing strategy is well-responsive to Gln without interference from other amino acids or Gln-containing peptides and is demonstrated to be useful for in situ Gln imaging in live cells. The study provides a new method for fluorescent imaging of Gln in live cells, which is envisioned to find interesting applications in understanding the roles of Gln in some physiological processes.

High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber Electrodes

Co-reporter:Jie Hao, Tongfang Xiao, Fei Wu, Ping Yu, and Lanqun Mao

Analytical Chemistry 2016 Volume 88(Issue 22) pp:11238

Publication Date(Web):October 14, 2016

DOI:10.1021/acs.analchem.6b03854

In vivo monitoring of pH in live brain remains very essential to understanding acid–base chemistry in various physiological processes. This study demonstrates a potentiometric method for in vivo monitoring of pH in the central nervous system with carbon fiber-based proton-selective electrodes (CF-H+ISEs) with high antifouling property. The CF-H+ISEs are prepared by formation of a H+-selective membrane (H+ISM) with polyvinyl chloride polymeric matrixes containing plasticizer bis(2-ethylhexyl)sebacate, H+ ionophore tridodecylamine, and ion exchanger potassium tetrakis(4-chlorophenyl)borate onto carbon fiber electrodes (CFEs). Both in vitro and in vivo studies demonstrate that the H+ISM exhibits strong antifouling property against proteins, which enables the CF-H+ISEs to well maintain the sensitivity and reversibility for pH sensing after in vivo measurements. Moreover, the CF-H+ISEs exhibit a good response to pH changes within a narrow physiological pH range from 6.0 to 8.0 in quick response time with high reversibility and selectivity against species endogenously existing in the central nervous system. The applicability of the CF-H+ISEs is illustrated by real-time monitoring of pH changes during acid–base disturbances, in which the brain acidosis is induced by CO2 inhalation and brain alkalosis is induced by bicarbonate injections. The results demonstrate that brain pH value rapidly decreases in the amygdaloid nucleus by ca. 0.14 ± 0.01 (n = 5) when the rats breath in pure CO2 gas, while increases in the cortex by about 0.77 ± 0.12 (n = 3) following intraperitoneal injection of 5 mmol/kg NaHCO3. This study demonstrates a new potentiometric method for in vivo measurement of pH change in the live brain of rats with high reliability.

Protein Pretreatment of Microelectrodes Enables in Vivo Electrochemical Measurements with Easy Precalibration and Interference-Free from Proteins

Co-reporter:Xiaomeng Liu, Meining Zhang, Tongfang Xiao, Jie Hao, Ruixin Li, and Lanqun Mao

Analytical Chemistry 2016 Volume 88(Issue 14) pp:7238

Publication Date(Web):June 21, 2016

DOI:10.1021/acs.analchem.6b01476

In vivo electrochemistry is one powerful strategy for probing brain chemistry. However, the decreases in sensitivity mainly caused by the adsorption of proteins onto electrode surface in short-term in vivo measurements unfortunately render great challenges in both electrode calibration and selectivity against the alternation of proteins. In this study, we observe that the pretreatment of carbon fiber microelectrodes (CFEs) with bovine serum albumin (BSA) would offer a simple but effective strategy to the challenges mentioned above. We verify our strategy for dopamine (DA) with conventionally used CFEs and for ascorbate with our previously developed carbon nanotube-modified CFEs. We find that, in artificial cerebral spinal fluid (aCSF) solution containing BSA, the current responses of the microelectrodes equilibrate shortly and the results for precalibration carried out in this solution are found to be almost the same as those for the postcalibration in pure aCSF. This observation offers a new solution to electrode calibration for in vivo measurements with a technical simplicity. Furthermore, we find that the use of BSA pretreated CFEs to replace bare CFEs would minimize the interference from the alternation of proteins in the brain. This study offers a new general and effective approach to in vivo electrochemistry with a high reliability and a simplified procedure.

Rational Design of Bioelectrochemically Multifunctional Film with Oxidase, Ferrocene, and Graphene Oxide for Development of in Vivo Electrochemical Biosensors

Co-reporter:Xiuyun Wang, Qian Li, Jingjing Xu, Shuo Wu, Tongfang Xiao, Jie Hao, Ping Yu, and Lanqun Mao

Analytical Chemistry 2016 Volume 88(Issue 11) pp:5885

Publication Date(Web):May 5, 2016

DOI:10.1021/acs.analchem.6b00720

This study demonstrates a new strategy to develop in vivo electrochemical biosensors through rational design and simple formation of bioelectrochemically multifunctional film (BMF). The BMF is rationally designed by first efficiently incorporating oxidase, ferrocene mediator, and graphene oxide into polymaleimidostyrene/polystyrene (PMS/PS) matrix to form a homogeneous mixture and then simply formed by drop-coating the mixture onto solid conducting substrate. By using the as-formed BMF, electrochemical biosensors could be constructed with a technical simplicity and high reproducibility. To illustrate the BMF-based biosensors for in vivo applications, we directly couple the biosensors to in vivo microdialysis to establish an online electrochemical system (OECS) for in vivo monitoring of glucose in rat auditory cortex during salicylate-induced tinnitus model. The OECS with the BMF-based biosensor as the detector shows a linear response toward glucose within a concentration range from 50 to 500 μM with a detection limit of 10 μM (S/N = 3). Additionally, the OECS is stable and does not suffer from the interference from the electroactive species endogenously coexisting in the brain microdialysate. With the BMF-based OECS, the basal level of glucose in the microdialysate continuously sampled from rat auditory cortex is determined to be 120 ± 10 μM (n = 5). After the rats were administrated with salicylate to induce transient tinnitus, the microdialysate glucose concentration in the rat auditory cortex remarkably increased to 433 ± 190 μM (n = 5) at the time point of 1.5 h. This study essentially offers a new, technically simple and reproducible approach to development of in vivo electrochemical biosensors, which is envisaged to be relatively useful for understanding of the molecular basis of brain functions.

An Online Electrochemical System for Continuously Monitoring Uric Acid Change following Rabbit Kidney following Ischemia-reperfusion Injury

Co-reporter:Yuqing Lin, Bo Li, Jie Hao, Tongfang Xiao, Yan Yang, Ping Yu, Lanqun Mao

Electrochimica Acta 2016 Volume 209() pp:132-137

Publication Date(Web):10 August 2016

DOI:10.1016/j.electacta.2016.05.054

In vivo monitoring of uric acid (UA) with high reliability and robustness is of great physiological and pathological importance because UA, as one kind of the most important chemical species in the biological systems, plays a great role in some physiological processes and is used as the biomarkers for early diagnosis of several diseases. In this study, a microfluidic chip-based online electrochemical system (OECS) is developed for the first time for continuously monitoring UA in rabbit kidney. To establish the OECS for UA monitoring, a single-channel microfluidic chip is developed into an electrochemical cell by incorporating a single-walled carbon nanotubes (SWNTs)-modified indium-tin oxide (ITO) electrode as working electrode, an Ag/AgCl wire as reference electrode, and a Pt tube as counter electrode. To completely remove ascorbic acid and thus eliminate its interference toward UA detection in such a single-channel microfluidic chip, ascorbate oxidase (AOx) is crosslinked onto both the etched ITO glass in the upstream channel and the SWNT-modified ITO electrode in the downstream. With the as-prepared microfluidic chip-based electrochemical cell as the detector for selective detection of UA, an online electrochemical system is successfully established by directly coupling the microfluidic chip-based electrochemical detector with in vivo microdialysis. The system exhibits a good linear response, high stability and good in vivo selectivity and is thus able to continuously sense UA change in rabbit kidney following ischemia-reperfusion injury. The study essentially offers a new OECS for in vivo continuous monitoring of UA.

Online electrochemical system as an in vivo method to study dynamic changes of ascorbate in rat brain during 3-methylindole-induced olfactory dysfunction

Co-reporter:Lijuan Li, Yinghong Zhang, Jie Hao, Junxiu Liu, Ping Yu, Furong Ma and Lanqun Mao

Analyst 2016 vol. 141(Issue 7) pp:2199-2207

Publication Date(Web):25 Feb 2016

DOI:10.1039/C6AN00064A

This study demonstrates the application of an online electrochemical system (OECS) as an in vivo method to investigate the dynamic change of microdialysate ascorbate in the olfactory bulb (OB) of rats during the acute period of olfactory dysfunction induced by intraperitoneal (i.p.) injection of 3-methylindole (3-MI). The OECS is developed by directly coupling an electrochemical detector to in vivo microdialysis for the direct monitoring of ascorbate. The system benefits from the good electrochemical activity of single-walled carbon nanotubes towards the oxidation of ascorbate and exhibits high selectivity, good stability, reproducibility and linearity for the measurement of ascorbate in the OB under physiological conditions. With this method, the basal level of microdialysate ascorbate in the OB is determined to be 48.64 ± 5.44 μM. The administration of 3-MI clearly increases the microdialysate ascorbate in the OB after 3-MI treatments and this increase is obviously alleviated by intravenous administration of ascorbate and glutathione (GSH) within 10 min after i.p. injection of 3-MI. These observations with the OECS suggest that ascorbate may be involved in chemical processes during the early stages of 3-MI-induced olfactory dysfunction. This study essentially validates the OECS as an in vivo method for effective measurement of ascorbate in the OB in rat brain and such a method will find interesting applications in investigating chemical process associated with ascorbate underlying olfactory dysfunction.

Simultaneous in vivo ascorbate and electrophysiological recordings in rat brain following ischemia/reperfusion

Co-reporter:Hanjun Cheng, Tongfang Xiao, Dalei Wang, Jie Hao, Ping Yu, Lanqun Mao

Journal of Electroanalytical Chemistry 2016 Volume 781() pp:90-96

Publication Date(Web):15 November 2016

DOI:10.1016/j.jelechem.2016.10.024

•An integrated dual-mode microelectrode (IDMME) was developed for synchronous neurochemical and neuroelectrical recordings.•No reciprocal interference between the two adjacent recording channels was observed during the concurrent recordings.•The changes of neurochemical and neuroelectrical signals of rats' brains were recorded at a high spatiotemporal resolution.Simultaneous recording of neurochemical signal and electrophysiological activity in the same brain region remains vitally essential to understanding the essences of physiological and pathological events because of the intrinsic chemical and electrical nature of communication between the neurons. However, the difficulty in selectively recording chemical signal with a high temporal resolution in chemically complex central nervous system presents a great challenge for achieving this goal. In this study, we demonstrate a method for simultaneous and real-time recording of ascorbate and electrical signals in live brain by using an integrated dual-mode microelectrode (IDMME), in which a single-walled carbon nanotube (SWNT)-modified carbon fiber microelectrode (CFME) was efficiently integrated with a glass microcapillary electrode. The SWNT-based CFME was served as an electrochemical recording channel to in vivo monitor cerebral ascorbate with a high selectivity and an improved temporal resolution, while the glass microcapillary electrode was employed as an electrophysiological recording channel for single-unit recording in the cerebral system. We found that no reciprocal interference between the two recording channels with the IDMME when constant-potential amperometry was employed for in vivo monitoring of ascorbate. The validity of the IDMME in neurochemical studies was illustrated by concurrently and real-time recording the dynamic changes of cortical ascorbate level and electrophysiological signal in the same brain region of live rats following ischemia/reperfusion. This study essentially offers an effective approach to in vivo monitoring of neurochemical and electrophysiological events in live brain, which is envisaged to be useful for understanding physiological processes involved in brain functions.Integrated dual-mode microelectrodes for in vivo simultaneous and real-time recording of neurochemical and electrical signals in live brain with a high temporal resolution.

Nonlinear dependence of the ion current rectification factor on bias voltage in conical nanopipettes

Co-reporter:Ting Li, Xiulan He, Ping Yu, Lanqun Mao

Journal of Electroanalytical Chemistry 2016 Volume 779() pp:106-111

Publication Date(Web):15 October 2016

DOI:10.1016/j.jelechem.2016.04.028

Ion current rectification (ICR), which is the departure of the experimentally measured current-voltage curves from ohmic behavior, has recently drawn intensive interests from both a fundamental point of view and microfluidic-based applications. In this case, the rectification factor (RF), which is defined as the absolute value of the quotient between the currents recorded for one voltage polarity and the currents recorded for the same absolute value of voltage at the opposite polarity, is one of the most important parameters to describe the rectification behavior. Herein, we interestingly observed that RF is strongly dependent on the bias voltage from both the experimental and theoretically simulated results, and this dependence exhibits nonlinear deviation with increasing the rectification degree. At the same surface charge density, the linear deviation increases with decreasing the electrolyte concentration. When the electrolyte concentration remains the same, the linear deviation increases with increasing the surface charge density. The simulated results demonstrate that the electro-osmotic flow is not the dominating factor to this nonlinear phenomenon. This nonlinear deviation is considered to possibly originate from the inhomogeneous conductivity and the nonlinear change of conductance with the bias potential. This study is not only useful to understanding the ICR behavior at a conical glass nanopipette, but also potentially offers a new parameter to describe the rectification degree with this nonlinear relationship.

Tuning interionic interaction for highly selective in vivo analysis

Co-reporter:Ping Yu, Xiulan He and Lanqun Mao

Chemical Society Reviews 2015 vol. 44(Issue 17) pp:5959-5968

Publication Date(Web):22 Jun 2015

DOI:10.1039/C5CS00082C

The development of highly selective methodologies to enable in vivo recording of chemical signals is of great importance for studying brain functions and brain activity mapping. However, the complexity of cerebral systems presents a great challenge in the development of chem/(bio)sensors that are capable of directly and selectively recording bioactive molecules involved in brain functions. As one of the most important and popular interactions in nature, interionic interaction constitutes the chemical essence of high specificity in natural systems, which inspires us to develop highly selective chem/(bio)sensors for in vivo analysis by precisely engineering interionic interaction in the in vivo sensing system. In this tutorial review, we focus on the recent progress in the tuning of interionic interaction to improve the selectivity of biosensors for in vivo analysis. The type and property of the interionic interaction is first introduced and several strategies to improve the selectivity of the biosensors, including enzyme-based electrochemical biosensors, aptamer-based electrochemical biosensors, and the strategies to recruit recognition molecules are reviewed. We also present an overview of the potential applications of the biosensors for in vivo analysis and thereby for physiological investigations. Finally, we present the major challenges and opportunities regarding the high selectivity of in vivo analysis based on tuning interionic interaction. We believe that this tutorial review provides critical insights for highly selective in vivo analysis and offers new concepts and strategies to understand brain chemistry.

Graphdiyne Oxides as Excellent Substrate for Electroless Deposition of Pd Clusters with High Catalytic Activity

Co-reporter:Hetong Qi; Ping Yu; Yuexiang Wang; Guangchao Han; Huibiao Liu; Yuanping Yi; Yuliang Li

Journal of the American Chemical Society 2015 Volume 137(Issue 16) pp:5260-5263

Publication Date(Web):April 14, 2015

DOI:10.1021/ja5131337

Graphdiyne (GDY), a novel kind of two-dimensional carbon allotrope consisting of sp- and sp2-hybridized carbon atoms, is found to be able to serve as the reducing agent and stabilizer for electroless deposition of highly dispersed Pd nanoparticles owing to its low reduction potential and highly conjugated electronic structure. Furthermore, we observe that graphdiyne oxide (GDYO), the oxidation form of GDY, can be used as an even excellent substrate for electroless deposition of ultrafine Pd clusters to form Pd/GDYO nanocomposite that exhibits a high catalytic performance toward the reduction of 4-nitrophenol. The high catalytic performance is considered to benefit from the rational design and electroless deposition of active metal catalysts with GDYO as the support.

Colorimetric and Fluorescent Dual Mode Sensing of Alcoholic Strength in Spirit Samples with Stimuli-Responsive Infinite Coordination Polymers

Co-reporter:Jingjing Deng, Wenjie Ma, Ping Yu, and Lanqun Mao

Analytical Chemistry 2015 Volume 87(Issue 13) pp:6958

Publication Date(Web):June 4, 2015

DOI:10.1021/acs.analchem.5b01617

This study demonstrates a new strategy for colorimetric and fluorescent dual mode sensing of alcoholic strength (AS) in spirit samples based on stimuli-responsive infinite coordination polymers (ICPs). The ICP supramolecular network is prepared with 1,4-bis(imidazol-1-ylmethyl)benzene (bix) as the ligand and Zn2+ as the central metal ion in ethanol, in which rhodamine B (RhB) is encapsulated through self-adaptive chemistry. In pure ethanol solvent, the as-formed RhB/Zn(bix) is well dispersed and quite stable. However, the addition of water into the ethanol dispersion of RhB/Zn(bix) destroys Zn(bix) network structure, resulting in the release of RhB from ICP into the solvent. As a consequence, the solvent displays the color of released RhB and, at the meantime, turns on the fluorescence of RhB, which constitutes a new mechanism for colorimetric and fluorescent dual mode sensing of AS in commercial spirit samples. With the method developed here, we could distinguish the AS of different commercial spirit samples by the naked eye within a wide linear range from 20 to 100% vol and by monitoring the increase of fluorescent intensity of the released RhB. This study not only offers a new method for on-spot visible detection of AS in commercial spirit samples, but also provides a strategy for designing dual mode sensing mechanisms for different analytical purposes based on novel stimuli-responsive materials.

Real-time Ratiometric Fluorescent Assay for Alkaline Phosphatase Activity with Stimulus Responsive Infinite Coordination Polymer Nanoparticles

Co-reporter:Jingjing Deng, Ping Yu, Yuexiang Wang, and Lanqun Mao

Analytical Chemistry 2015 Volume 87(Issue 5) pp:3080

Publication Date(Web):January 29, 2015

DOI:10.1021/ac504773n

This study demonstrates a novel ratiometric fluorescent method for real-time alkaline phosphatase (ALP) activity assay with stimulus responsive infinite coordination polymer (ICP) nanoparticles as the probe. The ICP nanoparticles used in this study are composed of two components; one is the supramolecular ICP network formed with guanine monophosphate (GMP) as the ligand and Tb3+ as the central metal ion, and the other is a fluorescent dye, i.e., 7-amino-4-methyl coumarin (coumarin) encapsulated into the ICP network. Upon being excited at 315 nm, the ICP network itself emits green fluorescence at 552 nm. Coumarin dye encapsulated in the ICP network emits weak fluorescence at 450 nm upon excitation at the same wavelength (315 nm), and this fluorescence emission becomes strong when the encapsulated dye is released from the network into the solution phase. Hence, we develop a ratiometric fluorescent assay based on the ALP-induced destruction of the supramolecular ICP network and the release of coumarin. This mechanism can be used for real-time ratiometric fluorescent monitoring of ALP activity by continuously measuring the ratio of fluorescent intensity at the wavelength of 552 nm (F552) to that at 450 nm (F450) (F552/F450) in the time-dependent fluorescent spectra of the coumarin@Tb-GMP suspension containing ALP with different activities. Under the experimental conditions employed here, the F552/F450 value is linear with the ALP activity within a range from 0.025 U/mL to 0.2 U/mL. The detection limit is down to 0.010 U/mL (S/N = 3). Moreover, the assay developed here is employed for ALP inhibitor evaluation. This study offers a simple yet sensitive method for real-time ALP activity assay.

Dual Recognition Unit Strategy Improves the Specificity of the Adenosine Triphosphate (ATP) Aptamer Biosensor for Cerebral ATP Assay

Co-reporter:Ping Yu, Xiulan He, Li Zhang, and Lanqun Mao

Analytical Chemistry 2015 Volume 87(Issue 2) pp:1373

Publication Date(Web):December 11, 2014

DOI:10.1021/ac504249k

Adenosine triphosphate (ATP) aptamer has been widely used as a recognition unit for biosensor development; however, its relatively poor specificity toward ATP against adenosine-5′-diphosphate (ADP) and adenosine-5′-monophosphate (AMP) essentially limits the application of the biosensors in real systems, especially in the complex cerebral system. In this study, for the first time, we demonstrate a dual recognition unit strategy (DRUS) to construct a highly selective and sensitive ATP biosensor by combining the recognition ability of aptamer toward A nucleobase and of polyimidazolium toward phosphate. The biosensors are constructed by first confining the polyimidazolium onto a gold surface by surface-initiated atom transfer radical polymerization (SI-ATRP), and then the aptamer onto electrode surface by electrostatic self-assembly to form dual-recognition-unit-functionalized electrodes. The constructed biosensor based on DRUS not only shows an ultrahigh sensitivity toward ATP with a detection limit down to the subattomole level but also an ultrahigh selectivity toward ATP without interference from ADP and AMP. The constructed biosensor is used for selective and sensitive sensing of the extracellular ATP in the cerebral system by combining in vivo microdialysis and can be used as a promising neurotechnology to probing cerebral ATP concentration.

An efficient electrocatalyst for oxygen reduction reaction derived from a Co-porphyrin-based covalent organic framework

Co-reporter:Wenjie Ma, Ping Yu, Takeo Ohsaka, Lanqun Mao

Electrochemistry Communications 2015 Volume 52() pp:53-57

Publication Date(Web):March 2015

DOI:10.1016/j.elecom.2015.01.021

•Pyrolysis of covalent organic frameworks (COFs) for construction of M/N/C ORR electrocatalysts.•Excellent electrocatalytic activity toward ORR, which is quite comparable to that of the commercial Pt/C.•A possible insight into the ORR at the M/N/C catalysts.A novel efficient electrocatalyst for oxygen reduction reaction (ORR) was synthesized by pyrolysis of a cobalt-based covalent organic framework, which shows electrocatalytic performance comparable with the commercial Pt/C for ORR via an almost four-electron pathway in alkaline media without methanol-crossover effect. This work not only provides a possible insight into the ORR at the M/N/C catalysts, but also paves a new route to the development of novel precious metal-free ORR electrocatalysts with high activities for ORR.

A multi-enzyme microreactor-based online electrochemical system for selective and continuous monitoring of acetylcholine

Co-reporter:Yuqing Lin, Ping Yu and Lanqun Mao

Analyst 2015 vol. 140(Issue 11) pp:3781-3787

Publication Date(Web):08 Dec 2014

DOI:10.1039/C4AN02089H

This study demonstrates an online electrochemical system (OECS) for selective and continuous measurements of acetylcholine (ACh) through efficiently integrating in vivo microdialysis, a multi-enzyme microreactor and an electrochemical detector. A multi-enzyme microreactor was prepared first by co-immobilizing two kinds of enzymes, i.e. choline oxidase (ChOx) and catalase (Cat), onto magnetite nanoparticles and then confining the as-formed nanoparticles into a fused-silica capillary with the assistance of an external magnet. The multi-enzyme microreactor was settled between an in vivo microdialysis sampling system and an electrochemical detector to suppress the interference from choline toward ACh detection. Selective detection of ACh was accomplished using the electrochemical detector with ACh esterase (AChE) and ChOx as the recognition units for ACh and Prussian blue (PB) as the electrocatalyst for the reduction of hydrogen peroxide (H2O2). The current recorded with the OECS was linear with the concentration of ACh (I/nA = −3.90CACh/μM + 1.21, γ = 0.998) within a concentration range of 5 μM to 100 μM. The detection limit, based on a signal-to-noise ratio of 3, was calculated to be 1 μM. Interference investigation demonstrates that the OECS did not produce an observable current response toward physiological levels of common electroactive species, such as ascorbic acid (AA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and uric acid (UA). The high selectivity and the good linearity in combination with the high stability may enable the OECS developed here as a potential system for continuous monitoring of cerebral ACh release in some physiological and pathological processes.

MnO2 nanosheets based fluorescent sensing platform with organic dyes as a probe with excellent analytical properties

Co-reporter:Chunxia Wang, Wanying Zhai, Yuexiang Wang, Ping Yu and Lanqun Mao

Analyst 2015 vol. 140(Issue 12) pp:4021-4029

Publication Date(Web):15 Apr 2015

DOI:10.1039/C5AN00581G

Manganese dioxide (MnO2) nanosheets have recently been demonstrated to be particularly attractive for fluorescent sensing and imaging; however, almost all MnO2 nanosheets-based fluorescent assays have been developed with emissive nanoparticles as the probes. In this study, we developed a novel strategy to use organic dyes, instead of emissive nanoparticles, as the probe to construct a platform for biosensing with excellent analytical properties. With 5-carboxyfluorescein (FAM) as a model organic dye, we firstly investigate the effect of MnO2 nanosheets on the fluorescence of FAM and find that the fluorescence intensity of FAM is considerably suppressed by MnO2 nanosheets based on the inner filter effect (IFE). To demonstrate that the MnO2 nanosheets-based fluorescence sensing platform can easily achieve a high selectivity with organic dyes as the probe, we use single-stranded DNA (ssDNA) oligonucleotide as a typical biorecognition unit, which is labeled with the FAM probe to form FAM-ssDNA. The fluorescent intensity of FAM-ssDNA is first suppressed by MnO2 nanosheets through the combination of IFE and Förster resonant energy transfer (FRET), and then recovered with subsequent hybridization with the complementary DNA oligonucleotide. To demonstrate the potential applications of the MnO2 nanosheets-based fluorescence sensing platform with organic dyes as the probes, we developed methods for simple but effective microRNA and thrombin assays. With the platform demonstrated here, the limits of detection for miR124a and thrombin are 0.8 nM and 11 nM, respectively. Moreover, the fluorescent sensing assay for thrombin exhibits high selectivity. This study essentially demonstrates a new 2D nanostructure-based fluorescent sensing platform that is robust, technically simple, and easily manipulated to achieve high selectivity and sensitivity for practical applications.

Online electrochemical systems for continuous neurochemical measurements with low-potential mediator-based electrochemical biosensors as selective detectors

Co-reporter:Zipin Zhang, Jie Hao, Tongfang Xiao, Ping Yu and Lanqun Mao

Analyst 2015 vol. 140(Issue 15) pp:5039-5047

Publication Date(Web):15 May 2015

DOI:10.1039/C5AN00593K

This study demonstrates a new strategy to develop online electrochemical systems (OECSs) for continuously monitoring neurochemicals by efficiently integrating in vivo microdialysis with an oxidase-based electrochemical biosensor with low-potential electron mediators to shuttle the electron transfer of the oxidases. By using thionine and xanthine oxidase (XOD) as examples of low-potential mediators and oxidases, respectively, we demonstrate that the use of low-potential mediators to shuttle the electron transfer of oxidases would offer a new approach to the development of oxidase-based biosensors with theoretical and technical simplicity. To construct the XOD-based biosensor, thionine was adsorbed onto carbon nanotubes and used to shuttle the electron transfer of XOD. The XOD-based biosensor was positioned into an electrochemical cell that was directly coupled with in vivo microdialysis to form an online electrochemical system (OECS) for continuous and selective measurements of the substrate of XOD (with hypoxanthine as an example). The OECS based on the low-potential mediators is highly selective against the species endogenously existing in the brain system, which is attributed to the low operation potential benefited from the low redox potentials of the mediators. Moreover, the OECS demonstrated here is stable and reproducible and could thus be envisaged to find some interesting applications in physiological and pathological investigations. This study essentially offers a new strategy to develop online electrochemical systems, which is of great importance in understanding the molecular basis of physiological and pathological events.

Ferricyanide-backfilled cylindrical carbon fiber microelectrodes for in vivo analysis with high stability and low polarized potential

Co-reporter:Peipei Zhong, Ping Yu, Kai Wang, Jie Hao, Junjie Fei and Lanqun Mao

Analyst 2015 vol. 140(Issue 21) pp:7154-7159

Publication Date(Web):07 Sep 2015

DOI:10.1039/C5AN01650A

The development of stable and reproducible methods for in vivo electrochemical monitoring of neurochemicals is of great physiological importance. In this study, we demonstrate ferricyanide-filled cylindrical carbon fiber microelectrodes (CFEs) of high stability and low polarized potential for in vivo electrochemical analysis. We first studied the voltammetric behavior of cylindrical CFEs by using a model system consisting of two separated cells each containing potassium ferricyanide (K3Fe(CN)6) or potassium ferrocyanide (K4Fe(CN)6). We observed that E1/2 values of the system were dependent on the ratio of the lengths of the cylindrical CFEs and of the concentrations of the redox species on both poles. Based on this property, we prepared the ferricyanide-backfilled cylindrical CFEs, and found that this kind of electrode exhibits a more stable current response and a lower polarized potential than the CFEs backfilled with KCl or Ru(NH3)6Cl3. Animal experiments with the ferricyanide-backfilled cylindrical CFEs demonstrate that this kind of electrode could be used for in vivo monitoring of neurochemical release with a high stability under some physiological conditions.

In vivo fluorescence sensing of the salicylate-induced change of zinc ion concentration in the auditory cortex of rat brain

Co-reporter:Qin Jiang, Zijian Guo, Yao Zhao, Fuyi Wang and Lanqun Mao

Analyst 2015 vol. 140(Issue 1) pp:197-203

Publication Date(Web):12 Sep 2014

DOI:10.1039/C4AN01443J

This study demonstrates a fluorescence method for in vivo sensing of the dynamic change of Zn2+ concentration in auditory cortex microdialysates induced by salicylate with N′-(7-nitro-2,1,3-benzoxadiazole-4-yl)-N,N,N′-tris(pyridine-2-ylmethyl) ethane-1,2-diamine (NBD-TPEA) as a probe. The excellent properties of the NBD-TPEA probe make it possible to achieve a high selectivity for Zn2+ sensing with the co-existence of amino acids and other metal ions as well as the species commonly existing in the cerebral system. To validate the method for in vivo fluorescence sensing of Zn2+ in the rat brain, we pre-mix the microdialysates in vivo sampled from the auditory cortex with the NBD-TPEA probe and then perfuse the mixtures into a fluorescent cuvette for continuous-flow fluorescence detection. The method demonstrated here shows a linear relationship between the signal output and Zn2+ concentration within the concentration range from 0.5 μM to 4 μM, with a detection limit of 156 nM (S/N = 3). The basal level of extracellular Zn2+ in auditory cortex microdialysates is determined to be 0.52 ± 0.082 μM (n = 4). This value is increased by the injection of 100 mg mL−1 of salicylate (1 μL min−1, 5 min, i.p.), reaches a peak at the time point of 90 min, and levels off with time. Such an increase is attenuated by the injection of MK-801, a potent and specific NMDA receptor antagonist, after the pre-injection of 100 mg mL−1 salicylate for 5 min. This study offers a fluorescence method for in vivo sensing of Zn2+ in the rat brain that could be useful for the investigations of chemical processes involved in brain functions.

In vivo and continuous measurement of bisulfide in the hippocampus of rat's brain by an on-line integrated microdialysis/droplet-based microfluidic system

Co-reporter:Feidan Gu, Xiaoyu Zhou, Xiaocui Zhu, Meiping Zhao, Jie Hao, Ping Yu and Lanqun Mao

Analyst 2015 vol. 140(Issue 11) pp:3814-3819

Publication Date(Web):05 Jan 2015

DOI:10.1039/C4AN01974A

An on-line and continuous approach was demonstrated for in vivo measurement of bisulfide in rat's brain. A modified droplet-based microfluidic system was constructed, which allowed on-line qualification of the fluorescence responses of the gold nanoparticle–glutathione–fluorescein isothiocyanate probe to the variation of bisulfide in the presence of the cerebral microdialysate background. The on-line method achieved a dynamic working range from 5.0 μM to 40 μM and a detection limit of 2.5 μM. The in vivo bisulfide concentration in the hippocampus of rat's brain was measured under different physiological conditions. The on-line method may facilitate the study of H2S biology by providing a previously unattainable continuous record of H2S variation in living animals. It also provides a practical platform for in vivo and continuous monitoring of other important species in cerebral systems.

Visualization and Quantification of Neurochemicals with Gold Nanoparticles: Opportunities and Challenges

Co-reporter:Jingjing Deng;Ping Yu;Yuexiang Wang;Lifen Yang

Advanced Materials 2014 Volume 26( Issue 40) pp:6933-6943

Publication Date(Web):

DOI:10.1002/adma.201305619

Gold nanoparticle (Au-NP)-based colorimetric assays offer new opportunitites for the visualization and quantification of neurochemicals involved in physiological and pathological processes due to their high sensitivity, designability, and low technical demands. In this Research News, we systematically review the advances on the development of Au-NP-based colorimetric methods for visualization and quantification of neurochemicals and their potential applications for effectively monitoring neurochemicals in the central nervous system. By integration of the favourable surface chemistry with the high extinction coefficient of Au-NPs, some new principles and methods could be developed for the quantification of neurochemicals involved in brain functions. New strategies to design the surface chemistry of Au-NPs, along with the key challenges yet to be addressed to achieve online visualization and quantification of neurochemicals in the central nervous system, are illustrated and discussed. The questions opened here should inspire future investigations and lead to discoveries that continue the development of the effective analytical protocols based on Au-NPs for neurochemical visualization and quantification.

Water-Stable, Adaptive, and Electroactive Supramolecular Ionic Material and Its Application in Biosensing

Co-reporter:Li Zhang, Hetong Qi, Jie Hao, Lifen Yang, Ping Yu, and Lanqun Mao

ACS Applied Materials & Interfaces 2014 Volume 6(Issue 8) pp:5988

Publication Date(Web):April 2, 2014

DOI:10.1021/am5011628

Developing water-stable and adaptive supramolecular materials is of great importance in various research fields. Here, we demonstrate a new kind of water-stable, adaptive, and electroactive supramolecular ionic materials (SIM) that is formed from the aqueous solutions of imidazolium-based dication and dianionic dye (i.e., 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS) through ionic self-assembly. The formed SIM not only shows good thermostability and unique optical and electrochemical properties that are raised from precursors of the SIM, but also exhibits good water-stability, salt-stability, and adaptive encapsulation properties toward some heterocyclic cationic dye molecules. UV–vis and FT-IR results demonstrate that this encapsulation property is essentially based on the electrostatic interactions between the guest dye molecules and ABTS in the SIM. The application of the SIM prepared here is illustrated by the development of a new electrochemical sensor for NADH sensing at a low potential. This study not only opens a new avenue to the preparation of the supramolecular materials, but also provides a versatile platform for electrochemical (bio)sensing.Keywords: adaptive encapsulation; biosensor; electrochemistry; supramolecular ionic materials; water-stable;

Single-Layer MnO2 Nanosheets Suppressed Fluorescence of 7-Hydroxycoumarin: Mechanistic Study and Application for Sensitive Sensing of Ascorbic Acid in Vivo

Co-reporter:Wanying Zhai, Chunxia Wang, Ping Yu, Yuexiang Wang, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 24) pp:12206

Publication Date(Web):November 13, 2014

DOI:10.1021/ac503215z

In this study, we systematically investigate the mechanism of single-layer MnO2 nanosheets suppressing fluorescence of 7-hydroxycoumarin and, based on this, demonstrate a new fluorescent method for in vivo sensing of ascorbic acid (AA) in rat brain. The mechanism for the fluorescence suppression is attributed to a combination of inner filter effect (IFE) and static quenching effect (SQE), which is different from those reported for the traditional two-dimensional nanosheets, and Förster resonant energy transfer (FRET) mechanism reported for MnO2 nanosheets. The combination of IFE and SQE leads to an exponential decay in fluorescence intensity of 7-hydroxycoumarin with increasing concentration of MnO2 nanosheets in solution. Such a property allows optimization of the concentration of MnO2 nanosheets in such a way that the addition of reductive analyte (e.g., AA) will to the greatest extent restore the MnO2 nanosheets-suppressed fluorescence of 7-hydroxycoumarin through the redox reaction between AA and MnO2 nanosheets. On the basis of this feature, we demonstrate a fluorescent method for in vivo sensing of AA in the cerebral systems with an improved sensitivity. Compared with the turn-on fluorescent method through first decreasing the fluorescence to the lowest level by adding concentrated MnO2 nanosheets, the method demonstrated here possesses a higher sensitivity, lower limit of detection, and wider linear range. Upon the use of ascorbate oxidase to achieve the selectivity for AA, the turn-on fluorescence method demonstrated here can be used for in vivo sensing of AA in a simple but reliable way.

1,5-Diaminonaphthalene Hydrochloride Assisted Laser Desorption/Ionization Mass Spectrometry Imaging of Small Molecules in Tissues Following Focal Cerebral Ischemia

Co-reporter:Huihui Liu, Rui Chen, Jiyun Wang, Suming Chen, Caiqiao Xiong, Jianing Wang, Jian Hou, Qing He, Ning Zhang, Zongxiu Nie, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 20) pp:10114

Publication Date(Web):September 23, 2014

DOI:10.1021/ac5034566

A sensitive analytical technique for visualizing small endogenous molecules simultaneously is of great significance for clearly elucidating metabolic mechanisms during pathological progression. In the present study, 1,5-naphthalenediamine (1,5-DAN) hydrochloride was prepared for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) of small molecules in liver, brain, and kidneys from mice. Furthermore, 1,5-DAN hydrochloride assisted LDI MSI of small molecules in brain tissue of rats subjected to middle cerebral artery occlusion (MCAO) was carried out to investigate the altered metabolic pathways and mechanisms underlying the development of ischemic brain damage. Our results suggested that the newly prepared matrix possessed brilliant features including low cost, strong ultraviolet absorption, high salt tolerance capacity, and fewer background signals especially in the low mass range (typically m/z < 500), which permitted us to visualize the spatial distribution of a broad range of small molecule metabolites including metal ions, amino acids, carboxylic acids, nucleotide derivatives, peptide, and lipids simultaneously. Nineteen endogenous metabolites involved in metabolic networks such as ATP metabolism, tricarboxylic acid (TCA) cycle, glutamate-glutamine cycle, and malate-aspartate shuttle, together with metal ions and phospholipids as well as antioxidants underwent relatively obvious changes after 24 h of MCAO. The results were highly consistent with the data obtained by MRM MS analysis. These findings highlighted the promising potential of the organic salt matrix for application in the field of biomedical research.

Effective Visualization Assay for Alcohol Content Sensing and Methanol Differentiation with Solvent Stimuli-Responsive Supramolecular Ionic Materials

Co-reporter:Li Zhang, Hetong Qi, Yuexiang Wang, Lifen Yang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 15) pp:7280

Publication Date(Web):July 13, 2014

DOI:10.1021/ac5014546

This study demonstrates a rapid visualization assay for on-spot sensing of alcohol content as well as for discriminating methanol-containing beverages with solvent stimuli-responsive supramolecular ionic material (SIM). The SIM is synthesized by ionic self-assembling of imidazolium-based dication C10(mim)2 and dianionic 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in water and shows water stability, a solvent stimuli-responsive property, and adaptive encapsulation capability. The rationale for the visualization assay demonstrated here is based on the combined utilization of the unique properties of SIM, including its water stability, ethanol stimuli-responsive feature, and adaptive encapsulation capability toward optically active rhodamine 6G (Rh6G); the addition of ethanol into a stable aqueous dispersion of Rh6G-encapsulated SIM (Rh6G-SIM) destructs the Rh6G-SIM structure, resulting in the release of Rh6G from SIM into the solvent. Alcohol content can thus be visualized with the naked eyes through the color change of the dispersion caused by the addition of ethanol. Alcohol content can also be quantified by measuring the fluorescence line of Rh6G released from Rh6G-SIM on a thin-layer chromatography (TLC) plate in response to alcoholic beverages. By fixing the diffusion distance of the mobile phase, the fluorescence line of Rh6G shows a linear relationship with alcohol content (vol %) within a concentration range from 15% to 40%. We utilized this visualization assay for on-spot visualizing of the alcohol contents of three Chinese commercial spirits and discriminating methanol-containing counterfeit beverages. We found that addition of a trace amount of methanol leads to a large increase of the length of Rh6G on TLC plates, which provides a method to identify methanol adulterated beverages with labeled ethanol content. This study provides a simple yet effective assay for alcohol content sensing and methanol differentiation.

Platinized Aligned Carbon Nanotube-Sheathed Carbon Fiber Microelectrodes for In Vivo Amperometric Monitoring of Oxygen

Co-reporter:Ling Xiang, Ping Yu, Meining Zhang, Jie Hao, Yuexiang Wang, Lin Zhu, Liming Dai, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 10) pp:5017

Publication Date(Web):April 29, 2014

DOI:10.1021/ac500622m

The abnormal level of O2 could disturb various neurochemical processes and even induce neural injury and brain dysfunction. In order to assess critical roles of O2 in the neurochemical processes, it is essential to perform in vivo monitoring of the dynamic changes of O2. In this study, we develop a new electrochemical method for selectively monitoring O2 in vivo, using platinized vertically aligned carbon nanotube (VACNT)-sheathed carbon fibers (Pt/VACNT-CFs) as the electrodes. The VACNT-sheathed CFs (VACNT-CFs) are produced via the pyrolysis of iron phthalocyanine (FePc) on the surface of CFs, followed by electrochemical deposition of platinum nanoparticles to form Pt/VACNT-CFs. The resulting Pt/VACNT-CF microelectrodes exhibit fast overall kinetics for the O2 reduction via a four-electron reduction process without the formation of toxic H2O2 intermediate. Consequently, effective and selective electrochemical methods are developed for the measurements of O2 in rat brain with the Pt/VACNT-CF microelectrodes, even in the presence of some species at their physiological levels, such as ascorbic acid, dopamine, uric acid, 5-hydroxytryptamine, and of the O2 fluctuation in rat brain in the early stage of global cerebral ischemia/reperfusion, mild hyperoxia, and hypoxia induced by exposing the animal, for a short time, to O2 and N2, respectively, and hindfeet pinch. The use of VACNT-CF as the support for Pt effectively improves the stability of Pt, as compared with the bare CF support, while the FePc pyrolysis ensures the VACNT-CFs to be reproducibly produced. Thus, this study offers a novel and reliable strategy for preparing new microelectrodes for in vivo monitoring of O2 in various physiological processes with a high sensitivity and selectivity.

Continuous and Simultaneous Electrochemical Measurements of Glucose, Lactate, and Ascorbate in Rat Brain Following Brain Ischemia

Co-reporter:Yuqing Lin, Ping Yu, Jie Hao, Yuexiang Wang, Takeo Ohsaka, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 8) pp:3895

Publication Date(Web):March 12, 2014

DOI:10.1021/ac4042087

Developing new tools and technologies to enable recording the dynamic changes of multiple neurochemicals is the essence of better understanding of the molecular basis of brain functions. This study demonstrates a microfluidic chip-based online electrochemical system (OECS) for in vivo continuous and simultaneous monitoring of glucose, lactate, and ascorbate in rat brain. To fabricate the microfluidic chip-based detecting system, a microfluidic chip with patterned channel is developed into an electrochemical flow cell by incorporating the chip with three surface-modified indium–tin oxide (ITO) electrodes as working electrodes, a Ag/AgCl wire as reference electrode, and a stainless steel tube as counter electrode. Selective detection of ascorbate is achieved by the use of single-walled carbon nanotubes (SWNTs) to largely facilitate the electrochemical oxidation of ascorbate, while a dehydrogenase-based biosensing mechanism with methylene green (MG) adsorbed onto SWNTs as an electrocatalyst for the oxidation of dihydronicotiamide adenine dinucleotide (NADH) is employed for biosensing of glucose and lactate. To avoid the crosstalk among three sensors, the sensor alignment is carefully designed with the SWNT-modified electrode in the upstream channel and paralleled glucose and lactate biosensors in the downstream channels. With the microfluidic chip-based electrochemical flow cell as the detector, an OECS is successfully established by directly integrating the microfluidic chip-based electrochemical flow cell with in vivo microdialysis. The OECS exhibits a good linear response toward glucose, lactate, and ascorbate with less crosstalk. This property, along with the high stability and selectivity, enables the OECS for continuously monitoring three species in rat brain following brain ischemia.

Vertically Aligned Carbon Nanotube-Sheathed Carbon Fibers as Pristine Microelectrodes for Selective Monitoring of Ascorbate in Vivo

Co-reporter:Ling Xiang, Ping Yu, Jie Hao, Meining Zhang, Lin Zhu, Liming Dai, and Lanqun Mao

Analytical Chemistry 2014 Volume 86(Issue 8) pp:3909

Publication Date(Web):March 21, 2014

DOI:10.1021/ac404232h

Using as-synthesized vertically aligned carbon nanotube-sheathed carbon fibers (VACNT-CFs) as microelectrodes without any postsynthesis functionalization, we have developed in this study a new method for in vivo monitoring of ascorbate with high selectivity and reproducibility. The VACNT-CFs are formed via pyrolysis of iron phthalocyanine (FePc) on the carbon fiber support. After electrochemical pretreatment in 1.0 M NaOH solution, the pristine VACNT-CF microelectrodes exhibit typical microelectrode behavior with fast electron transfer kinetics for electrochemical oxidation of ascorbate and are useful for selective ascorbate monitoring even with other electroactive species (e.g., dopamine, uric acid, and 5-hydroxytryptamine) coexisting in rat brain. Pristine VACNT-CFs are further demonstrated to be a reliable and stable microelectrode for in vivo recording of the dynamic increase of ascorbate evoked by intracerebral infusion of glutamate. Use of a pristine VACNT-CF microelectrode can effectively avoid any manual electrode modification and is free from person-to-person and/or electrode-to-electrode deviations intrinsically associated with conventional CF electrode fabrication, which often involves electrode surface modification with randomly distributed CNTs or other pretreatments, and hence allows easy fabrication of highly selective, reproducible, and stable microelectrodes even by nonelectrochemists. Thus, this study offers a new and reliable platform for in vivo monitoring of neurochemicals (e.g., ascorbate) to largely facilitate future studies on the neurochemical processes involved in various physiological events.

Improving the fluorescence detection limit with positively charged carbon nanostructures as a low background signal platform

Co-reporter:Xiulan He, Li Zhang, Hetong Qi, Ping Yu, Junjie Fei and Lanqun Mao

Analyst 2014 vol. 139(Issue 9) pp:2114-2117

Publication Date(Web):31 Jan 2014

DOI:10.1039/C4AN00124A

We have demonstrated a new strategy to improve the fluorescence detection limit by enhancing the energy transfer efficiency between carbon structures and fluorescent dyes using polyimidazolium-functionalized carbon nanostructures as a low background signal platform. Based on this, a highly sensitive method for thrombin was proposed with a detection limit as low as 2.79 pM without any amplification.

Recent progress in highly efficient Ag-based visible-light photocatalysts

Co-reporter:Gaiping Li, Yuexiang Wang and Lanqun Mao

RSC Advances 2014 vol. 4(Issue 96) pp:53649-53661

Publication Date(Web):03 Oct 2014

DOI:10.1039/C4RA08044K

As one of the most promising and efficient approaches for remediating the deterioration of natural environments, semiconductor-based photocatalysis has received considerable attention. To date, numerous efforts have been focused to explore novel materials for highly efficient photocatalysis under visible light or sunlight irradiation. Among them, Ag-based compounds are emerging to be a promising candidate because of their excellent visible light-responsive photoelectrochemical properties. This review summarizes the recent progress in the design and fabrication of Ag-compound-based semiconductor photocatalysts and their applications in the photocatalytic decomposition of organic molecules. Initially, the mechanisms of the related photocatalytic reactions will be discussed, and then we will highlight some of the recent progresses in Ag-based micro- or nano-structured material fabrication that exhibit enhanced photocatalytic performance. These novel and highly efficient photocatalysts mainly include Ag2O, Ag2S, AgX (X = Cl, Br, I), Ag2CO3 and Ag3PO4. We expect that the present tutorial review will provide insights in the direction of the future visible-light photocatalyst design.

Rapid and Cost-Effective Synthesis of Nanosized Zeolitic Imidazolate Framework-7 with N,N-Dimethylformamide as Solvent and Metal Acetate Salt as Metal Source

Co-reporter:Xiang Wang;Pengcheng Huang;Ping Yu;Lifen Yang

ChemPlusChem 2014 Volume 79( Issue 7) pp:907-913

Publication Date(Web):

DOI:10.1002/cplu.201402052

Abstract

In this study, a new method was developed for the rapid and cost-effective synthesis of nanosized zeolitic imidazolate framework-7 (ZIF-7) nanocrystals with a high yield and a low molar ratio of benzimidazole ligand to metal salt (2:1) by using N,N′-dimethylformamide (DMF) as the solvent and zinc acetate dihydrate (Zn(OAc)₂⋅2 H₂O) as the metal source. The synthesized ZIF-7 nanocrystals have a size of approximately 50–80 nm, and tend to aggregate or become intergrown to form irregular nanoparticles of about 200–300 nm in size. The morphology and yield of the ZIF-7 nanocrystals can be tuned easily by changing the synthetic parameters such as the composition of the solvent and concentrations of reagents. The synthesized ZIF-7 nanocrystals exhibit good thermal and chemical stability, CO₂ capture capability, and fluorescent properties. Remarkably, we find that the synthetic strategy developed here can be extended to the syntheses of other kinds of ZIFs including ZIF-69 and ZIF-90. This study offers a new, simple synthetic strategy for the high-yield preparation of ZIF materials.

Electrochemical Post-Treatment of Infinite Coordination Polymers: An Effective Route to Preparation of Pd Nanoparticles Supported onto Carbon Nanotubes with Enhanced Electrocatalytic Activity toward Ethanol Oxidation

Co-reporter:Lin Ren, Lifen Yang, Ping Yu, Yuexiang Wang, and Lanqun Mao

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 21) pp:11471

Publication Date(Web):October 10, 2013

DOI:10.1021/am403996d

This study describes an effective method to prepare highly dispersed palladium nanoparticles supported onto single-walled carbon nanotubes (SWNTs) with high electrocatalytic activity toward the oxidation of ethanol. This method is essentially based on electrochemical post-treatment of Pd-based infinite coordination polymer (ICP). The Pd-based ICP is synthesized through the coordination reaction between Zn2+ and metallo-Schiff base (MSB) to form Zn-MSB-Zn (ZMZ) ICP that precipitates from ethyl ether. The as-formed Zn-MSB-Zn ICP is then subjected to an ion-exchange reaction with Pd2+ to obtain the Zn-MSB-Pd (ZMP) ICP. To prepare Pd/SWNT nanocomposite, the ZMP ICP is mixed into the SWNT dispersion in N-dimethylformamide (DMF) to form a homogeneous dispersion that is then drop-coated onto a glassy carbon (GC) electrode. Electrochemical post-treatment of ZMP ICP to form Pd/SWNT nanocomposite is thus performed by polarizing the coated electrode at −0.2 V for 600 s in 0.5 M H2SO4. The results obtained with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that the resulting Pd nanoparticles are highly dispersed onto SWNTs and the particles size are small and narrowly distributed (2.12 ± 0.32 nm). X-ray photoelectron spectroscopy (XPS) analysis shows that, after the electrochemical post-treatment, no detectable ZMP ICP precursors are left on the surface of SWNTs. The electrocatalytic activity of the as-formed Pd/SWNT nanocomposite toward ethanol oxidation is investigated by cyclic voltammetry and chronoamperometry. The results show that the Pd/SWNT nanocomposite prepared here shows a more negative potential and higher mass catalytic activity, as well as higher stability for the oxidation of ethanol than the commercial Pd/C catalyst. This work demonstrates a novel approach to the formation of ultrasmall and highly dispersed Pd/SWNT nanocomposite with enhanced electrocatalytic activity toward ethanol oxidation.Keywords: electrochemical post-treatment; ethanol electrooxidation; infinite coordination polymers; palladium nanoparticles;

Photodecomposition of Ferrocenedicarboxylic Acid in Methanol to Form an Electroactive Infinite Coordination Polymer and Its Application in Bioelectrochemistry

Co-reporter:Li Zhang, Xia Gao, Lifen Yang, Ping Yu, and Lanqun Mao

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 16) pp:8120

Publication Date(Web):July 9, 2013

DOI:10.1021/am402189s

Accurately characterizing the product of photodecomposition of ferrocene derivatives remains a longstanding challenge due to its structural complexity and strong dependence on the solvent and the substituent. Herein, photodecomposition of ferrocenedicarboxylic acid (FcDC) in methanol is found for the first time to form an electroactive infinite coordinate polymer (ICP) with uniform size, good water stability and photostability, and excellent electrochemical activity. The possible mechanism for the ICP formation is proposed based on the fission of the Fe-ring bond and deprotonation of FcDC under light irradiation. The dissociated Fe2+ is first oxidized to Fe3+ that consequently coordinates with the deprotonated ferrocene dicarboxylate to produce ICP nanoparticles. This work not only provides a new insight into the product formation of the photodecomposition of ferrocene derivatives but also offers a mild and simple route to the synthesis of electroactive ICPs.Keywords: bioelectrochemistry; ferrocenedicarboxylic acid; infinite coordination polymer; laccase; photodecomposition;

Alkaline Post-Treatment of Cd(II)–Glutathione Coordination Polymers: Toward Green Synthesis of Water-Soluble and Cytocompatible CdS Quantum Dots with Tunable Optical Properties

Co-reporter:Pengcheng Huang, Qin Jiang, Ping Yu, Lifen Yang, and Lanqun Mao

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:5239

Publication Date(Web):May 13, 2013

DOI:10.1021/am401082n

In this study, we demonstrate a facile and environmentally friendly method for the synthesis of glutathione (GSH)-capped water-soluble CdS quantum dots (QDs) with a high cytocompatibility and a tunable optical property based on alkaline post-treatment of Cd–GSH coordination polymers (CPs). Cd–GSH CPs are synthesized with the coordination reaction of Cd2+ with GSH at different pH values, and the CdS QDs are then formed by adding NaOH to the aqueous dispersion of the Cd–GSH CPs to break the coordination interaction between Cd2+ and GSH with the release of sulfur. The particle size and optical property of the as-formed CdS QDs are found to be easily tailored by simply adjusting the starting pH values of GSH solutions used for the formation of Cd–GSH CPs, in which the wavelengths of trap-state emission of the QDs red-shift with an increase in the sizes of the QDs that is caused by an increase in the starting pH values of GSH solutions. In addition, the use of GSH as the capping reagent eventually endows the as-formed CdS QDs with enhanced water solubility and good cytocompatibility, as demonstrated with HeLa cells. The method demonstrated here is advantageous in that the cadmium precursor and the sulfur source are nontoxic and easily available, and the size, optical properties, water solubility, and cytocompatibilty of the as-formed CdS QDs are simply achieved and experimentally regulated. This study offers a new and green synthetic route to water-soluble and cytocompatible CdS QDs with tunable optical properties.Keywords: CdS quantum dots; coordination polymers; cytocompatibility; glutathione; green synthesis; water solubility;

Online Electrochemical Monitoring of Dynamic Change of Hippocampal Ascorbate: Toward a Platform for In Vivo Evaluation of Antioxidant Neuroprotective Efficiency against Cerebral Ischemia Injury

Co-reporter:Kun Liu, Ping Yu, Yuqing Lin, Yuexiang Wang, Takeo Ohsaka, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 20) pp:9947

Publication Date(Web):September 20, 2013

DOI:10.1021/ac402620c

Effective monitoring of cerebral ascorbate following intravenous antioxidant treatment is of great importance in evaluating the antioxidant efficiency for neuroprotection because ascorbate is closely related to a series of ischemia-induced neuropathological processes. This study demonstrates the validity of an online electrochemical system (OECS) for ascorbate detection as a platform for in vivo evaluation of neuroprotective efficiency of antioxidants by studying the dynamic change of hippocampal ascorbate during the acute period of cerebral ischemia and its responses to intravenous administration of antioxidants including ascorbate and glutathione (GSH). The OECS consists of a selective electrochemical detector made of a thin-layer electrochemical flow cell integrated with in vivo microdialysis. With such a system, the basal level of hippocampal ascorbate is determined to be 5.18 ± 0.60 μM (n = 20). This level is increased by 10 min of two-vessel occlusion (2-VO) ischemia treatment and reaches 11.51 ± 3.43 μM (n = 5) at the time point of 60 min after the ischemia. The 2-VO ischemia-induced hippocampal ascorbate increase is obviously attenuated by immediate intravenous administration of ascorbate (2.94 g/kg) or glutathione (5.12 g/kg) within 10 min after ischemia and the ascorbate level remains to be 3.75 ± 1.66 μM (n = 4) and 5.30 ± 0.79 μM (n = 5), respectively, at the time point of 60 min after ischemia. To confirm if the attenuated hippocampal ascorbate increase is attributed to the antioxidant-induced oxidative stress alleviation, we further study the immunoreactivity of 8-hydroxy-2-deoxyguanosine (8-OHdG) in the ischemic hippocampus and find that the 8-OHdG immunoreactivity is decreased by the administration of ascorbate or GSH as compared to the ischemic brain without antioxidant treatment. These results substantially demonstrate that the OECS for ascorbate detection could be potentially used as a platform for evaluating the efficiency of antioxidant neuroprotection in cerebral ischemia treatment.

Real-Time Colorimetric Assay of Inorganic Pyrophosphatase Activity Based on Reversibly Competitive Coordination of Cu2+ between Cysteine and Pyrophosphate Ion

Co-reporter:Jingjing Deng, Qin Jiang, Yuexiang Wang, Lifen Yang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 19) pp:9409

Publication Date(Web):September 9, 2013

DOI:10.1021/ac402524e

In this study we demonstrate a new colorimetric method for real-time pyrophosphatase (PPase) activity assay based on reversible tuning of the dispersion/aggregation states of gold nanoparticles (Au-NPs) by controlling the coordination of Cu2+ between cysteine and pyrophosphate ion (PPi) with PPase. The addition of Cu2+ to the cysteine-stabilized Au-NP dispersion results in the aggregation of Au-NPs, while the further addition of PPi to this aggregation turns the aggregated Au-NPs into their dispersed state because of the higher coordination reactivity between Cu2+ and PPi than that between Cu2+ and cysteine. The subsequent addition of PPase to the PPi-triggered dispersed Au-NPs restores the aggregation state of Au-NPs because PPase catalyzes the hydrolysis of PPi into orthophosphate and thus consumes PPi in the reaction system. In this study, we utilize this reversibility of the change between the aggregation/dispersion states of Au-NPs for real-time colorimetric monitoring of PPase activity by continuously measuring the ratio of absorbance at the wavelength of 650 nm (A650) to that at 522 nm (A522) in the time-dependent UV–vis spectra of Au-NP dispersions containing different activities of PPase. To calculate the kinetics of the PPase-catalyzed hydrolysis of PPi, the A650/A522 values are converted into PPi concentrations to obtain the time-dependent changes of PPi concentrations in the dispersions containing different activities of PPase. The initial reaction rates (v0) are thus achieved from the time-dependent logarithm of PPi concentrations with the presence of different PPase activities. Under the experimental conditions employed here, the v0 values are linear with the PPase activity within a range from 0.025 to 0.4 U with a detection limit down to 0.010 U (S/N = 3). Moreover, the colorimetric method developed here is also employed for PPase inhibitor evaluation. This study offers a simple yet effective method for real-time PPase activity assay.

Zeolitic Imidazolate Framework-Based Electrochemical Biosensor for in Vivo Electrochemical Measurements

Co-reporter:Wenjie Ma, Qin Jiang, Ping Yu, Lifen Yang, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 15) pp:7550

Publication Date(Web):July 2, 2013

DOI:10.1021/ac401576u

This study demonstrates the first exploitation of zeolitic imidazolate frameworks (ZIFs) as the matrix for constructing integrated dehydrogenase-based electrochemical biosensors for in vivo measurement of neurochemicals, such as glucose. In this study, we find that ZIFs are able to serve as a matrix for coimmobilizing electrocatalysts (i.e., methylene green, MG) and dehydrogenases (i.e., glucose dehydrogenase, GDH) onto the electrode surface and an integrated electrochemical biosensor is readily formed. We synthesize a series of ZIFs, including ZIF-7, ZIF-8, ZIF-67, ZIF-68, and ZIF-70 with different pore sizes, surface areas, and functional groups. The adsorption capabilities toward MG and GDH of these ZIFs are systematically studied with UV–vis spectroscopy, confocal laser scanning microscopy, and Fourier transfer-infrared spectroscopy. Among all the ZIFs demonstrated here, ZIF-70 shows excellent adsorption capacities toward both MG and GDH and is thus employed as the matrix for our glucose biosensor. To construct the biosensor, we first drop-coat a MG/ZIF-70 composite onto a glassy carbon electrode and then coat GDH onto the MG/ZIF-70 composite. In a continuous-flow system, the as-prepared ZIF-based biosensor is very sensitive to glucose with a linear range of 0.1–2 mM. Moreover, the ZIF-based biosensor is more highly selective on glucose than on other endogenous electroactive species in the cerebral system. In the end, we demonstrate that our biosensor is capable of monitoring dialysate glucose collected from the brain of guinea pigs selectively and in a near real-time pattern.

Microfluidic Chip-Based Online Electrochemical Detecting System for Continuous and Simultaneous Monitoring of Ascorbate and Mg2+ in Rat Brain

Co-reporter:Xia Gao, Ping Yu, Yuexiang Wang, Takeo Ohsaka, Jianshan Ye, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 15) pp:7599

Publication Date(Web):July 9, 2013

DOI:10.1021/ac401727d

This study demonstrates a microfluidic chip-based online electrochemical detecting system for in vivo continuous and simultaneous monitoring of ascorbate and Mg2+ in rat brain. In this system, a microfluidic chip is used as the detector for both species. To fabricate the detector, a single-channel microfluidic chip is developed into an electrochemical flow cell by incorporating the chip with an indium–tin oxide (ITO) electrode as working electrode, an Ag/AgCl wire as reference electrode, and a stainless steel tube as counter electrode. Selective detection of ascorbate and Mg2+ is achieved by drop-coating single-walled carbon nanotubes (SWNTs) and polymerizing toluidine blue O (polyTBO) film onto the ITO electrode, respectively. Moreover, the alignment of SWNT-modified and polyTBO-modified electrodes and the solution introduction pattern are carefully designed to avoid any cross talk between two electrodes. With the microfluidic chip-based electrochemical flow cell as the detector, an online electrochemical detecting system is successfully established by directly integrating the microfluidic chip-based electrochemical flow cell with in vivo microdialysis. The microfluidic system exhibits sensing properties with a linear relationship from 5 to 100 μM for ascorbate and from 100 to 2000 μM for Mg2+. Moreover, this system demonstrates a high selectivity and stability and good reproducibility for simultaneous measurements of ascorbate and Mg2+ in a continuous-flow system. These excellent properties substantially render this system great potential for continuous and simultaneous online monitoring of ascorbate and Mg2+ in rat brain.

Hybridization of Bioelectrochemically Functional Infinite Coordination Polymer Nanoparticles with Carbon Nanotubes for Highly Sensitive and Selective In Vivo Electrochemical Monitoring

Co-reporter:Xulin Lu, Hanjun Cheng, Pengcheng Huang, Lifen Yang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 8) pp:4007

Publication Date(Web):March 17, 2013

DOI:10.1021/ac303743a

This study demonstrates the formation of a three-dimensional conducting framework through hybridization of bioelectrochemically active infinite coordination polymer (ICP) nanoparticles with single-walled carbon nanotubes (SWNTs) for highly sensitive and selective in vivo electrochemical monitoring with combination with in vivo microdialysis. The bioelectrochemically active ICP nanoparticles are synthesized through the self-assembly process of NAD+ and Tb3+, in which all biosensing elements including an electrocatalyst (i.e., methylene green, MG), cofactor (i.e., β-nicotinamide adenine dinucleotide, NAD+), and enzyme (i.e., glucose dehydrogenase, GDH) are adaptively encapsulated. The ICP/SWNT-based biosensors are simply prepared by drop-coating the as-formed ICP/SWNT nanocomposite onto a glassy carbon substrate. Electrochemical studies demonstrate that the simply prepared ICP/SWNT-based biosensors exhibit excellent biosensing properties with a higher sensitivity and stability than the ICP-based biosensors prepared only with ICP nanoparticles (i.e., without hybridization of SWNTs). By using a GDH-based electrochemical biosensor as an example, we demonstrate a technically simple yet effective online electroanalytical platform for continuously monitoring glucose in the brain of guinea pigs with the ICP/SWNT-based biosensor as an online detector in a continuous-flow system combined with in vivo microdialysis. Under the experimental conditions employed here, the dynamic linear range for glucose with the ICP/SWNT-biosensor is from 50 to 1000 μM. Moreover, in vivo selectivity investigations with the biosensors prepared by the GDH-free ICPs reveal that ICP/SWNT-based biosensors are very selective for the measurement of glucose in the cerebral system. The basal level of glucose in the microdialysates from the striatum of guinea pigs is determined to be 0.31 ± 0.03 mM (n = 3). The study offers a simple route to the preparation of electrochemical biosensors, which is envisaged to be particularly useful for probing the chemical events involved in some physiological and pathological processes.

Anion-Exchange-Based Amperometric Assay for Heparin Using Polyimidazolium as Synthetic Receptor

Co-reporter:Hetong Qi, Li Zhang, Lifen Yang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 6) pp:3439

Publication Date(Web):February 28, 2013

DOI:10.1021/ac400201c

This study demonstrates a facile yet effective strategy for amperometric assay of electrochemically inactive heparin based on an anion-exchange mechanism with polyimidazolium (Pim) as the synthetic receptor. The rationale for the amperometric heparin assay is essentially based on the different binding affinity of the synthetic Pim receptor toward electrochemically active ferricyanide (Fe(CN)63–) and electrochemically inactive heparin. To accomplish the amperometric assay, Pim is first synthesized and used as the artificial receptor to recognize the anions (i.e., Fe(CN)63– and heparin). The stronger binding affinity of the synthetic Pim receptor toward heparin than toward Fe(CN)63– essentially validates the amperometric heparin assay through an anion-exchange mechanism with the decrease in the redox peak current of Fe(CN)63– adsorbed onto the Pim film as the signal readout. The anion exchange between Fe(CN)63– and heparin on the Pim receptor is verified by cyclic voltammetry and Fourier transform IR and UV–visible spectroscopies. The ratio of the current decrease shows a linear relationship with heparin concentration with a concentration range from 0.5 to 10 μM. With animal experiments by dosing intraperitoneally and collecting the serum sample, the method is demonstrated to be potentially useful for investigating heparin metabolism in the biological system. This study not only provides a simple yet effective route to a heparin assay but also opens a new way to developing amperometric methods for electrochemically inert species by fully utilizing the supramolecular principles.

Competitive Coordination of Cu2+ between Cysteine and Pyrophosphate Ion: Toward Sensitive and Selective Sensing of Pyrophosphate Ion in Synovial Fluid of Arthritis Patients

Co-reporter:Jingjing Deng, Ping Yu, Lifen Yang, and Lanqun Mao

Analytical Chemistry 2013 Volume 85(Issue 4) pp:2516

Publication Date(Web):January 22, 2013

DOI:10.1021/ac303698p

Direct selective and sensitive sensing of pyrophosphate ion (PPi) in synovial fluid of arthritis patients is of great importance because of its crucial roles in the diagnosis and therapy of arthritic diseases. In this study, we demonstrate a sensitive and selective method for PPi sensing in synovial fluid of arthritis patients with gold nanoparticles (Au-NPs) as the signal readout based on the competitive coordination chemistry of Cu2+ between cysteine and PPi. Initially, Au-NPs stabilized with cysteine are red in color and exhibit absorption at 519 nm in the UV–vis spectrum. The addition of an aqueous solution of Cu2+ to the Au-NPs dispersion containing cysteine causes the aggregation of Au-NPs, resulting in the wine red-to-blue color change and the appearance of a new absorption at 650 nm in the UV–vis spectrum of the Au-NPs dispersion. The subsequent addition of PPi to the Au-NPs aggregation well solubilizes the aggregated Au-NPs with the changes in both the color and the UV–vis spectrum of the Au-NPs dispersion. These changes are ascribed to the higher coordination reactivity between Cu2+ and PPi than that between Cu2+ and cysteine. On the basis of this, the concentration of PPi can be visualized with the naked eyes through the blue-to-wine red color change of the Au-NPs dispersion and quantitatively determined by UV–vis spectroscopy. Under the optimized conditions, the ratio of the absorbance at 650 nm (A650) to that at 519 nm (A519) shows a linear relationship with PPi concentration within a concentration range from 130 nM to 1.3 mM. The method demonstrated here is highly sensitive, free from the interference from other species in the synovial fluid, and is thus particularly useful for fast and simple clinic diagnosis of arthritic diseases.

Charge–transfer interaction between melamine and quinones: Towards voltammetric determination of melamine

Co-reporter:Limin Zhang, Ting Li, Ping Yu, Takeo Ohsaka, Lanqun Mao

Electrochemistry Communications 2013 Volume 26() pp:89-92

Publication Date(Web):January 2013

DOI:10.1016/j.elecom.2012.10.026

This communication describes a new voltammetric method for the determination of melamine based on the charge–transfer interaction between quinones and melamine. Three types of quinones, i.e., tetrachloro-p-benzoquinone (TCBQ), benzoquinone (BQ), and vitamin K1 (VK1) were employed in this study. The charge–transfer interaction activity of quinones with melamine was found to depend on the structure of quinones, of which TCBQ with four electron-withdrawing chloro groups exhibits the highest interaction activity with melamine. Such a property was further employed for the voltammetric determination of melamine based on the decrease in the redox peak currents of TCBQ/TCBQ− caused by the pre-consumption of TCBQ with melamine. Under the conditions employed in this study, the decrease in the peak current of TCBQ was linear with the concentration of melamine within a concentration range from 10 μM to 1.0 mM.Highlights► UV–vis spectroscopic and electrochemical demonstration on the charge–transfer interaction between TCBQ and melamine ► Calculation of kinetics and thermodynamics of the interaction ► A facile and straightforward approach to voltammetric detection of melamine.

Cysteine-modulated colorimetric sensing of extracellular Mg2+ in rat brain based on the strong chelation interaction between dithiothreitol and Mg2+

Co-reporter:Xuming Zhuang, Dalei Wang, Lifen Yang, Ping Yu, Wei Jiang and Lanqun Mao

Analyst 2013 vol. 138(Issue 10) pp:3046-3052

Publication Date(Web):15 Mar 2013

DOI:10.1039/C3AN00235G

Simple and effective measurement of Mg2+ in the brain of living animals is of great physiological and pathological importance. In this study, we report a facile yet highly selective colorimetric method for effective sensing of cerebral Mg2+. The method is based on rational design of surface chemistry of gold nanoparticles (Au-NPs) with functional molecules including 1,4-dithiothreitol (DTT) and cysteine, enabling the fine tuning of the surface chemistry of Au-NPs in such a way that the addition of Mg2+ into the Au-NPs dispersion could selectively trigger the change of the dispersion/aggregation states of Au-NPs. The strong chelation interaction between Mg2+ and the hydroxyls in 1,4-dithiothreitol and the co-existence of cysteine on the surface of Au-NPs could, on one hand, enable the selective colorimetric detection of Mg2+ and, on the other hand, avoid the aggregation of Au-NPs induced by DTT itself. As a result, the addition of Mg2+ into the dispersion of the Au-NPs containing both cysteine and DTT results in the changes in both the color and the UV-vis spectra of the Au-NPs dispersion. The signal readout shows a linear relationship of Mg2+ within the concentration range from 1 μM to 40 μM with a detection limit of 800 nM (S/N = 3). Moreover, the assay demonstrated here is free from the interference of some physiological species commonly existing in rat brain. Although Ca2+ could interfere with the detection of Mg2+ because of its strong chelation with DTT, it could be selectively masked by masking agent (i.e., ethyleneglcol-bis (2-aminoethylether) tetraacetic acid). By combining the microdialysis technique, the basal dialysate level of Mg2+ is determined to be 299.2 ± 41.1 μM (n = 3) in the cerebral systems. The method essentially offers a new method for the detection of Mg2+ in the cerebral system.

Biofuel cell-based self-powered biogenerators for online continuous monitoring of neurochemicals in rat brain

Co-reporter:Hanjun Cheng, Ping Yu, Xulin Lu, Yuqing Lin, Takeo Ohsaka and Lanqun Mao

Analyst 2013 vol. 138(Issue 1) pp:179-185

Publication Date(Web):23 Oct 2012

DOI:10.1039/C2AN36385B

This study demonstrates a new electrochemical method for continuous neurochemical sensing with a biofuel cell-based self-powered biogenerator as the detector for the analysis of microdialysate continuously sampled from rat brain, with glucose as an example analyte. To assemble a glucose/O2 biofuel cell that can be used as a self-powered biogenerator for glucose sensing, glucose dehydrogenase (GDH) was used as the bioanodic catalyst for the oxidation of glucose with methylene green (MG) adsorbed onto single-walled carbon nanotubes (SWNTs) as the electrocatalyst for the oxidation of dihydronicotinamide adenine dinucleotide (NADH). Laccase crosslinked onto SWNTs was used as the biocathodic catalyst for the O2 reduction. To enable the bioanode and biocathode to work efficiently in their individually favorable solutions and to eliminate the interference between the glucose bioanode and O2 biocathode, the biofuel cell-based biogenerator was built in a co-laminar microfluidic chip so that the bioanodic and biocathodic streams could be independently optimized to provide conditions favorable for each of the bioelectrodes. By using a home-made portable voltmeter to output the voltage generated on an external resistor, the biogenerator was used for glucose sensing based on a galvanic cell mechanism. In vitro experiments demonstrate that, under the optimized conditions, the voltage generated on an external resistor shows a linear relationship with the logarithmic glucose concentration within a concentration range of 0.2 mM to 1.0 mM. Moreover, the biogenerator exhibits a high stability and a good selectivity for glucose sensing. The validity of the biofuel cell-based self-powered biogenerator for continuous neurochemical sensing was illustrated by online continuous monitoring of striatum glucose in rat brain through the combination of in vivo microdialysis. This study offers a new and technically simple platform for continuously monitoring physiologically important species in cerebral systems.

Silver Phosphate/Carbon Nanotube-Stabilized Pickering Emulsion for Highly Efficient Photocatalysis

Co-reporter:Wanying Zhai, Gaiping Li, Ping Yu, Lifen Yang, and Lanqun Mao

The Journal of Physical Chemistry C 2013 Volume 117(Issue 29) pp:15183-15191

Publication Date(Web):July 3, 2013

DOI:10.1021/jp404456a

This study demonstrates a first exploitation of the unique properties inherent in Pickering emulsions to develop a new kind of photocatalytic system. We engineered the system by using silver phosphate (Ag3PO4) as a photocatalytic active metal oxide semiconductor and multiwalled carbon nanotubes (MWNTs) as a hydrophobic conducting nanostructure to form the Pickering emulsions. The photocatalytic activity of the as-formed Ag3PO4/MWNT-stabilized Pickering emulsion-based system is studied toward dye decomposition and oxygen evolution. Results imply that the Pickering emulsion-based photocatalytic system exhibits a much higher efficiency, as compared with traditional solution-dispersed photocatalytic system. This high efficiency is elucidated in terms of the unique properties inherent in Pickering emulsions including (i) the self-assembled Ag3PO4/MWNT nanohybrid at water/oil interface, well ensuring a large surface area of the photocatalyst, (ii) the use of MWNTs to facilitate the formation of amphiphilic nanostructures self-assembled at water/oil interface, promoting the charge separation of the semiconductor through the π–π network of MWNTs by shuttling and storing photogenerated electrons from the visible light irradiated Ag3PO4, and (iii) the separation of the product (e.g., O2 evolved from water oxidation) from the reactants during the photocatalytic process, well accelerating the photocatalytic reactions. In addition to the high efficiency, the fast and simple procedures employed for demulsifying (e.g., sonication or centrifugation) and re-emulsifying (e.g., shaking) essentially make our Pickering emulsion-based photocatalytic system technically simple and thus practically applicable. This study opens a new way to developing novel photocatalytic systems with high efficiency and good practical applicability based on Pickering emulsion science and technology.

In vivo electrochemical recording of continuous change of magnesium in medial vestibular nucleus following vertigo induced by ice water vestibular stimulation

Co-reporter:Ying Xin;ZiPin Zhang;Ping Yu;FuRong Ma

Science China Chemistry 2013 Volume 56( Issue 2) pp:256-261

Publication Date(Web):2013 February

DOI:10.1007/s11426-012-4567-0

Vertigo is one of the most common clinical symptoms. However, the chemical processes involved in the pathological mechanism of vertigo remain to be fully understood. In this study, we investigate the dynamic changes in the magnesium (Mg2+) concentration in medial vestibular nucleus (MVN) of guinea pigs following vertigo induced by vestibular ice water stimulation with an electrochemical detection method consisting of in vivo microdialysis and on-line selective electrochemical detection. Electrochemical detection of Mg2+ was accomplished based on the current enhancement of Mg2+ towards the electrocatalytic oxidation of NADH at the electrodes modified with the polymerized film of toluidine blue O (TBO). Selectivity for the on-line electrochemical detection against Ca2+ was achieved by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca2+. The basal level of the extracellular Mg2+ in the MVN of guinea pigs was determined to be 759.7 ± 176.2 μM(n = 16). Upon ice water irrigation of the left external ear canal, the concentration of Mg2+ in the MVN decreases significantly, reaches 72 ± 6% (n = 8) of the basal level, and maintains for at least 1000 s. Control experiments reveal that neither warm water irrigation of the external ear canal nor ice water irrigation of the auricle induces the decrease in the concentration of Mg2+ in the MVN. These results demonstrate that the extracellular Mg2+ in the MVN decreases significantly following vertigo induced by vestibular ice water stimulation. This demonstration suggests that Mg2+ might play an important role in the pathological mechanism of vertigo.

Rational Design of Surface/Interface Chemistry for Quantitative in Vivo Monitoring of Brain Chemistry

Co-reporter:Meining Zhang, Ping Yu, and Lanqun Mao

Accounts of Chemical Research 2012 Volume 45(Issue 4) pp:533

Publication Date(Web):January 11, 2012

DOI:10.1021/ar200196h

To understand the molecular basis of brain functions, researchers would like to be able to quantitatively monitor the levels of neurochemicals in the extracellular fluid in vivo. However, the chemical and physiological complexity of the central nervous system (CNS) presents challenges for the development of these analytical methods. This Account describes the rational design and careful construction of electrodes and nanoparticles with specific surface/interface chemistry for quantitative in vivo monitoring of brain chemistry.We used the redox nature of neurochemicals at the electrode/electrolyte interface to establish a basis for monitoring specific neurochemicals. Carbon nanotubes provide an electrode/electrolyte interface for the selective oxidation of ascorbate, and we have developed both in vivo voltammetry and an online electrochemical detecting system for continuously monitoring this molecule in the CNS. Although Ca2+ and Mg2+ are involved in a number of neurochemical signaling processes, they are still difficult to detect in the CNS. These divalent cations can enhance electrocatalytic oxidation of NADH at an electrode modified with toluidine blue O. We used this property to develop online electrochemical detection systems for simultaneous measurements of Ca2+ and Mg2+ and for continuous selective monitoring of Mg2+ in the CNS.We have also harnessed biological schemes for neurosensing in the brain to design other monitoring systems. By taking advantage of the distinct reaction properties of dopamine (DA), we have developed a nonoxidative mechanism for DA sensing and a system that can potentially be used for continuously sensing of DA release. Using “artificial peroxidase” (Prussian blue) to replace a natural peroxidase (horseradish peroxidase, HRP), our online system can simultaneously detect basal levels of glucose and lactate. By substituting oxidases with dehydrogenases, we have used enzyme-based biosensing schemes to develop a physiologically relevant system for detecting glucose and lactate in rat brain. Because of their unique optical properties and modifiable surfaces, gold nanoparticles (Au-NPs) have provided a platform of colorimetric assay for in vivo cerebral glucose quantification. We designed and modified the surfaces of Au-NPs and then used a sequence of reactions to produce hydroxyl radicals from glucose.

Strong Interaction between Imidazolium-Based Polycationic Polymer and Ferricyanide: Toward Redox Potential Regulation for Selective In Vivo Electrochemical Measurements

Co-reporter:Xuming Zhuang, Dalei Wang, Yuqing Lin, Lifen Yang, Ping Yu, Wei Jiang, and Lanqun Mao

Analytical Chemistry 2012 Volume 84(Issue 4) pp:1900-1906

Publication Date(Web):January 22, 2012

DOI:10.1021/ac202748s

This study effectively demonstrates a strategy to enable the ferricyanide-based second-generation biosensors for selective in vivo measurements of neurochemicals, with glucose as an example. The strategy is based on regulation of redox potential of ferricyanide mediator by carefully controlling the different adsorption ability of ferricyanide (Fe(CN)63-) and ferrocyanide (Fe(CN)64-) onto electrode surface. To realize the negative shift of the redox potential of Fe(CN)63-/4-, imidazolium-based polymer (Pim) is synthesized and used as a matrix for surface adsorption of Fe(CN)63-/4- due to its stronger interaction with Fe(CN)63- than with Fe(CN)64-. The different adsorption ability of Fe(CN)63- and Fe(CN)64- onto electrodes modified with a composite of Pim and multiwalled carbon nanotubes (MWNTs) eventually enables the stable surface adsorption of both species to generate integrated biosensors and, more importantly, leads to a negative shift of the redox potential of the surface-confined redox mediator. Using glucose oxidase (GOD) as the model biorecognition units, we demonstrate the validity of the ferricyanide-based second-generation biosensors for selective in vivo neurochemical measurements. We find that the biosensors developed with the strategy demonstrated in this study can be used well as the selective detector for continuous online detection of striatum glucose of guinea pigs, by integration with in vivo microdialysis. This study essentially paves a new avenue to developing electrochemical biosensors effectively for in vivo neurochemical measurements, which is envisaged to be of great importance in understanding the molecular basis of physiological and pathological events.

An Electrochemical Method for Investigation of Conformational Flexibility of Active Sites of Trametes versicolor Laccase Based on Sensitive Determination of Copper Ion with Cysteine-Modified Electrodes

Co-reporter:Xianchan Li, Ping Yu, Lifen Yang, Fuyi Wang, and Lanqun Mao

Analytical Chemistry 2012 Volume 84(Issue 21) pp:9416

Publication Date(Web):September 27, 2012

DOI:10.1021/ac302241a

This study demonstrates a facile yet effective electrochemical method to investigate the conformational flexibility of the active sites of Trametes versicolor (Tv) laccase based on sensitive determination of copper ions (Cu2+) dissociated from the enzyme with the cysteine-modified Au electrodes. In the native state, the multicopper active sites are deeply buried in the polypeptide of Tv laccase and are thus not electrochemically detectable even at the cysteine-modified Au electrodes. Upon the unfolding of Tv laccase induced by guanidine hydrochloride (GdnHCl), copper ions dissociate from the peptide chain and, as a consequence, are electrochemically reduced and thus detected at the cysteine-modified Au electrodes. Such a property could be used to investigate the conformational flexibility of multicopper active sites of Tv laccase in a simple way. We find that both the conformation of the multicopper active sites in Tv laccase and the enzyme activity change with the presence of a low concentration of GdnHCl denaturant (midpoint, where 50% of the enzyme is unfolded, at 0.7 M). This concentration is lower than that required to induce the conformational changes of Tv laccase molecule as a whole (midpoint at 3.4 M), as investigated by the intrinsic fluorescence of Tv laccase. This observation suggests that the multicopper active sites are formed by relatively weak interactions and hence may be conformationally more flexible than the intact enzyme. The electrochemical method demonstrated in this study is technically simple yet effective and could be potentially useful for investigation on the thermodynamics and kinetics of the conformational changes of multicopper oxidases induced by different denaturants.

Aspartic Acid-Promoted Highly Selective and Sensitive Colorimetric Sensing of Cysteine in Rat Brain

Co-reporter:Qin Qian, Jingjing Deng, Dalei Wang, Lifen Yang, Ping Yu, and Lanqun Mao

Analytical Chemistry 2012 Volume 84(Issue 21) pp:9579

Publication Date(Web):October 2, 2012

DOI:10.1021/ac3024608

Direct selective determination of cysteine in the cerebral system is of great importance because of the crucial roles of cysteine in physiological and pathological processes. In this study, we report a sensitive and selective colorimetric assay for cysteine in the rat brain with gold nanoparticles (Au-NPs) as the signal readout. Initially, Au-NPs synthesized with citrate as the stabilizer are red in color and exhibit absorption at 520 nm. The addition of an aqueous solution (20 μL) of cysteine or aspartic acid alone to a 200 μL Au-NP dispersion causes no aggregation, while the addition of an aqueous solution of cysteine into a Au-NP dispersion containing aspartic acid (1.8 mM) causes the aggregation of Au-NPs and thus results in the color change of the colloid from wine red to blue. These changes are ascribed to the ion pair interaction between aspartic acid and cysteine on the interface between Au-NPs and solution. The concentration of cysteine can be visualized with the naked eye and determined by UV–vis spectroscopy. The signal output shows a linear relationship for cysteine within the concentration range from 0.166 to 1.67 μM with a detection limit of 100 nM. The assay demonstrated here is highly selective and is free from the interference of other natural amino acids and other thiol-containing species as well as the species commonly existing in the brain such as lactate, ascorbic acid, and glucose. The basal dialysate level of cysteine in the microdialysate from the striatum of adult male Sprague–Dawley rats is determined to be around 9.6 ± 2.1 μM. The method demonstrated here is facile but reliable and durable and is envisaged to be applicable to understanding the chemical essence involved in physiological and pathological events associated with cysteine.

Continuous Electrochemical Monitoring of Extracellular Lactate Production from Neonatal Rat Cardiomyocytes following Myocardial Hypoxia

Co-reporter:Xianchan Li, Lingzhi Zhao, Zhenling Chen, Yuqing Lin, Ping Yu, and Lanqun Mao

Analytical Chemistry 2012 Volume 84(Issue 12) pp:5285

Publication Date(Web):May 18, 2012

DOI:10.1021/ac300354z

Continuous monitoring of lactate production from cardiomyocytes is of great physiological and pathological importance since the level of lactate in extracellular fluid is closely associated with myocardial energy metabolism with implication in the diagnosis and therapeutics of myocardial hypoxia and ischemia. This study demonstrates an electrochemical approach to continuous monitoring of lactate production from neonatal rat cardiomyocytes following myocardial hypoxia with a dehydrogenase-based electrochemical biosensor and a negative pressure driven culture sampling. To eliminate the effect of pH variation occurring following the cardiomyocyte hypoxia on the biosensor response and to supply nicotinamide adenine dinucleotide (NAD+) cofactor necessary for the enzymatic reaction of lactate dehydrogenase (LDH), artificial cerebrospinal fluid (aCSF) containing NAD+ cofactor is externally perfused and mixed online with cell culture before the culture goes to the detector. The method exhibits a high selectivity against the electrochemically active species endogenously existing in the extracellular culture of cardiomyocytes and a high tolerance against the variation of pH following cardiomyocyte hypoxia. The dynamic linear range for lactate detection is from 0.20 to 10 mM (I (nA) = 25.6 CLactate (mM) + 20.1, γ = 0.996) with a detection limit of 0.16 mM (S/N = 3). The physiological level of the extracellular lactate of neonatal rat cardiomyocytes is determined to be 1.1 ± 0.1 mM (n = 3) with the cell density of about 0.5 × 103 cells/mm2. When the cardiomyocytes are subject to hypoxia induced with anoxic reagents, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), the extracellular lactate increases to 255 ± 30.3% (n = 3), relative to the physiological level, following 20 min of the hypoxia. This study essentially offers a new and effective electrochemical platform for investigating energy metabolism during cardiac physiological and pathological processes.

In Vivo Electrochemical Monitoring of the Change of Cochlear Perilymph Ascorbate during Salicylate-Induced Tinnitus

Co-reporter:Junxiu Liu, Ping Yu, Yuqing Lin, Na Zhou, Tao Li, Furong Ma, and Lanqun Mao

Analytical Chemistry 2012 Volume 84(Issue 12) pp:5433

Publication Date(Web):May 28, 2012

DOI:10.1021/ac301087v

As one of the most important neurochemicals in biological systems, ascorbate plays vital roles in many physiological and pathological processes. In order to understand the roles of ascorbate in the pathological process of tinnitus, this study demonstrates an in vivo method for real time monitoring of the changes of ascorbate level in the cochlear perilymph of guinea pigs during the acute period of tinnitus induced by local microinfusion of salicylate with carbon fiber microelectrodes (CFMEs) modified with multiwalled carbon nanotubes (MWNTs). To accomplish in vivo electrochemical monitoring of ascorbate in the microenvironment of the cochlear perilymph, the MWNT-modified CFME is used as working electrode, a microsized Ag/AgCl is used as reference electrode, and Pt wire is used as counter electrode. Three electrodes are combined together around a capillary to form integrated capillary-electrodes. The integrated capillary-electrode is carefully implanted into the cochlear perilymph of guinea pigs and used both for externally microinfusing of salicylate into the cochlear perilymph and for real time monitoring of the change of ascorbate levels. The in vivo voltammetric method based on the integrated capillary-electrodes possesses a high selectivity and a good linearity for ascorbate determination in the cochlear perilymph of guinea pigs. With such a method, the basal level of cochlear perilymph ascorbate is determined to be 45.0 ± 5.1 μM (n = 6). The microinfusion of 10 mM salicylate (1 μL/min, 5 min) into the cochlear decreases the ascorbate level to 28 ± 10% of the basal level (n = 6) with a statistical significance (P < 0.05), implying that the decrease in ascorbate level in the cochlear may be associated with salicylate-induced tinnitus. This study essentially offers a new method for in vivo monitoring of the cochlear perilymph ascorbate following the salicylate-induced tinnitus and can thus be useful for investigation on chemical essences involved in tinnitus.

Electricity generation from carboxymethyl cellulose biomass: A new application of enzymatic biofuel cells

Co-reporter:Hanjun Cheng, Qin Qian, Xiang Wang, Ping Yu, Lanqun Mao

Electrochimica Acta 2012 Volume 82() pp:203-207

Publication Date(Web):1 November 2012

DOI:10.1016/j.electacta.2011.11.122

Exploitation of naturally abundant biomass to produce electricity has been a hot topic. This study demonstrates for the first time a new application of enzymatic biofuel cells (BFCs) for direct production of electricity from carboxymethyl cellulose (CMC) biomass. As one of the most important cellulose derivates, CMC can be easily obtained from cellulose and has a good solubility in water. To produce electricity from CMC, cellulase was used as the biocatalyst in solution to catalyze the hydrolysis of CMC into glucose and glucose was then used as the biomass to produce electricity through biofuel cell technology. The bioanode for the oxidation of glucose produced for cellulase-catalyzed CMC hydrolysis was constructed with glucose dehydrogenase (GDH) as the biocatalyst and with methylene green (MG) adsorbed onto single-walled carbon nanotubes (SWNTs) as the electrocatalyst for the oxidation of NADH. The biocathode for the reduction of oxygen was fabricated by crosslinking laccase onto SWNTs. To catalyze CMC hydrolysis into glucose, 0.5 mg/mL cellulase was added into 1 wt.% CMC solution in 0.10 M acetate buffer (pH 5.5) and the mixture was then allowed to stand for 1 h to give CMC hydrolyzed solution. Under these conditions, CMC was hydrolyzed into glucose and glucose was oxidized under the biocatalysis of GDH, as characterized with UV–vis spectroscopy. In the CMC hydrolyzed solution containing NAD+ cofactor, both the bioanode and biocathode exhibit a good bioelectrocatalytic activity toward the oxidation of glucose and the reduction of oxygen, respectively. With the presence of 10 mM NAD+ into the CMC hydrolyzed solution, the assembled BFC has an open circuit voltage of 0.75 V and a maximum power output of 128 μW cm−2 at 0.35 V under ambient air and room temperature. These values are comparable to or even higher than those with other techniques employed to produce electricity from cellulose or cellulose derivates. This study essentially opens a new application of biofuel cell technology for energy production from naturally abundant biomass.

Electrocatalytic four-electron reduction of oxygen with Copper (II)-based metal-organic frameworks

Co-reporter:Junjie Mao, Lifen Yang, Ping Yu, Xianwen Wei, Lanqun Mao

Electrochemistry Communications 2012 Volume 19() pp:29-31

Publication Date(Web):June 2012

DOI:10.1016/j.elecom.2012.02.025

This communication describes the first demonstration on the use of metal-organic frameworks (MOFs) as electrocatalysts for oxygen reduction reaction (ORR). Copper (II) benzene-1,3,5-tricarboxylate (Cu-BTC, BTC = 1,3,5-tricarboxylate) was first synthesized and studied with respect to its electrocatalytic activity toward ORR. However, this kind of widely studied Cu(II)-based MOF was structurally unstable in aqueous media. We thus synthesized one kind of water-stable Cu(II)-based MOF, i.e., copper (II)-2,2′-bipyridine-benzene-1,3,5-tricarboxylate (Cu-bipy-BTC, bipy = 2,2′-bipyridine) as an alternative to Cu-BTC for the ORR study. In a phosphate buffer (pH 6.0), the synthetic Cu-bipy-BTC shows a couple of well-defined redox peaks at ca. − 0.15 V. The presence of O2 into the buffer clearly increases the reduction peak current, while decreases the reversed oxidation peak current of the redox wave. This property, along with the positive shift of the potential for ORR at the MOF-modified electrode compared with that at the bare GC electrode, demonstrates the electrocatalytic activity of the Cu-bipy-BTC MOF towards ORR. Rotating ring-disk electrode voltammetry reveals that this kind of MOF can catalyze the ORR through an almost four-electron reduction pathway. This study essentially offers a new approach to development of non-platinum ORR catalysts based on MOF materials.Highlights► A first demonstration on the application of MOFs for electrocatalytic ORR. ► Cu-bipy-BTC has excellent electrocatalytic activity for 4e-reduction of O2. ► A new route to design non-platinum electrocatalysts for ORR.

Sensitive and selective voltammetric measurement of Hg2+ by rational covalent functionalization of graphene oxide with cysteamine

Co-reporter:Heng Zhou, Xiang Wang, Ping Yu, Xiaoming Chen and Lanqun Mao

Analyst 2012 vol. 137(Issue 2) pp:305-308

Publication Date(Web):07 Nov 2011

DOI:10.1039/C1AN15793K

We report here a new voltammetric method for the sensitive and selective determination of Hg2+ based on rational covalent functionalization of graphene oxide with cysteamine to form cysteamine-functionalized graphene through nucleophilic ring-opening reaction between the epoxy of graphene oxide and the amino group of cysteamine in KOH solution.

Energy-efficient electrodeposition of metal-based nanostructures through simultaneous deposition at both the cathode and the anode

Co-reporter:Lin Ren, Jie Yan, Ping Yu and Lanqun Mao

Physical Chemistry Chemical Physics 2012 vol. 14(Issue 27) pp:9768-9773

Publication Date(Web):04 May 2012

DOI:10.1039/C2CP41393K

To meet the energy and environmental requirements, an effective strategy is demonstrated to enable electrochemistry to be energy-efficient for deposition of metal-based nanoparticles, based on careful design of the surface/interface reactions of metal precursors in such a way that the deposition can be induced at both the anode and the cathode.

Electrochemical impedance spectroscopic measurements of FCCP-induced change in membrane permeability of MDCK cells

Co-reporter:Lingzhi Zhao, Xianchan Li, Yuqing Lin, Lifen Yang, Ping Yu and Lanqun Mao

Analyst 2012 vol. 137(Issue 9) pp:2199-2204

Publication Date(Web):29 Feb 2012

DOI:10.1039/C2AN35064E

This study demonstrates a new electrochemical impedance spectroscopic (EIS) method for measurements of the changes in membrane permeability during the process of cell anoxia. Madin-Darby canine kidney (MDCK) cells were employed as the model cells and were cultured onto gelatin-modified glassy carbon (GC) electrodes. EIS measurements were conducted at the MDCK/gelatin-modified GC electrodes with Fe(CN)63−/4− as the redox probe. The anoxia of the cells grown onto electrode surface was induced by the addition of carbonycyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) into the cell culture, in which the MDCK/gelatin-modified GC electrodes were immersed for different times. The EIS results show that the presence of FCCP in the cell culture clearly decreases the charge-transfer resistance of the Fe(CN)63−/4− redox probe at the MDCK/gelatin-modified GC electrodes, and the charge-transfer resistance decreases with increasing time employed for immersing the MDCK/gelatin-modified GC electrodes into the cell culture containing FCCP. These results demonstrate that the EIS method could be used to monitor the changes in the cell membrane permeability during the FCCP-induced cell anoxia. To simulate the EIS system, a rational equivalent circuit was proposed and the values of ohmic resistance of the electrolyte, charge-transfer resistance and constant phase elements for both the gelatin and the cell layers are given with the fitting error in an acceptable value. This study actually offers a new and simple approach to measuring the dynamic process of cell death induced by anoxia through monitoring the changes in the cell membrane permeability.

Magnetically separable Fe3O4–Ag3PO4 sub-micrometre composite: facile synthesis, high visible light-driven photocatalytic efficiency, and good recyclability

Co-reporter:Gaiping Li and Lanqun Mao

RSC Advances 2012 vol. 2(Issue 12) pp:5108-5111

Publication Date(Web):26 Mar 2012

DOI:10.1039/C2RA20504A

A magnetically separable Fe3O4–Ag3PO4 sub-micrometre composite was synthesized in large quantities by a fast and simple route, and was demonstrated to have a high photocatalytic efficiency toward the decomposition of methylene blue dye under visible light irradiation with a good recyclability.

Ionic Liquid-Assisted Preparation of Laccase-Based Biocathodes with Improved Biocompatibility

Co-reporter:Qin Qian, Lei Su, Ping Yu, Hanjun Cheng, Yuqing Lin, Xiaoyong Jin, and Lanqun Mao

The Journal of Physical Chemistry B 2012 Volume 116(Issue 17) pp:5185-5191

Publication Date(Web):April 12, 2012

DOI:10.1021/jp3006475

Laccase enzyme has been widely used as the catalyst of the biocathodes in enzymatic biofuel cells (BFCs); the poor biocompatibility of this enzyme (e.g., poor catalytic activity in neutral media and low tolerance against chloride ion) and the lack of selectivity for oxygen reduction at the laccase-based biocathode against ascorbic acid, unfortunately, offer a great limitation to future biological applications of laccase-based BFCs. This study demonstrates a facial yet effective solution to these limitations with the assistance of hydrophobic room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (Bmim+PF6–). With the Bmim+PF6– overcoating, the laccase-based biocathodes possess a good bioelectrocatalytic activity toward O2 reduction in neutral media and a high tolerance against Cl–. Moreover, the Bmim+PF6– overcoating applied to the laccase-based biocathodes also well suppresses the oxidation of ascorbic acid (AA) at the biocathodes and thereby avoids the AA-induced decrease in the power output of the laccase-based BFCs. The mechanisms underlying the excellent properties of the Bmim+PF6– overcoating are proposed based on the intrinsic features of ionic liquid Bmim+PF6–. To demonstrate the applications of the BFCs with the as-prepared biocathodes in biologically relevant systems, an AA/O2 BFC is assembled with single-walled carbon nanotubes (SWNTs) as electrode materials both for accelerating AA oxidation at the bioanode and for promoting direct electron transfer of laccase at the biocathode. With the presence of 0.50 mM AA in 0.10 M quiescent phosphate buffer (pH 7.2), the assembled BFC has an open circuit voltage of 0.73 V and a maximum power output of 24 μW cm–2 at 0.40 V under ambient air and room temperature. This study essentially offers a new strategy for the development of enzymatic BFCs with a high biocompatibility.

Rational Design and One-Step Formation of Multifunctional Gel Transducer for Simple Fabrication of Integrated Electrochemical Biosensors

Co-reporter:Ping Yu, Heng Zhou, Hanjun Cheng, Qin Qian, and Lanqun Mao

Analytical Chemistry 2011 Volume 83(Issue 14) pp:5715

Publication Date(Web):June 6, 2011

DOI:10.1021/ac200942a

This study demonstrates a new strategy to simplify the biosensor fabrication and thus minimize the biosensor-to-biosensor deviation through rational design and one-step formation of a multifunctional gel electronic transducer integrating all elements necessitated for efficiently transducing the biorecognition events to signal readout, by using glucose dehydrogenase (GDH) based electrochemical biosensor as an example. To meet the requirements for preparing integrated biosensors and retaining electronic and ionic conductivities for electronically transducing process, ionic liquids (ILs) with enzyme cofactor (i.e., oxidized form of nicotinamide adenine dinucleotide) as the anion were synthesized and used to form a bucky gel with single-walled carbon nanotubes, in which methylene green electrocatalyst was stably encapsulated for the oxidation of nicotinamide adenine dinucleotide. With such kind of rationally designed and one-step-formed multifunctional gel as the electronic transducer, the GDH-based electrochemical biosensors were simply fabricated by polishing the electrodes onto the gel followed by enzyme immobilization. This capability greatly simplifies the biosensor fabrication, prolongs the stability of the biosensors, and, more remarkably, minimizes the biosensor-to-biosensor deviation. The relative standard deviations obtained both with one electrode for the repeated measurements of glucose and with the different electrodes prepared with the same method for the concurrent measurements of glucose with the same concentration were 3.30% (n = 7) and 4.70% (n = 6), respectively. These excellent properties of the multifunctional gel-based biosensors substantially enable them to well-satisfy the pressing need of rapid measurements, for example, environmental monitoring, food analysis, and clinical diagnoses.

Graphene as a Spacer to Layer-by-Layer Assemble Electrochemically Functionalized Nanostructures for Molecular Bioelectronic Devices

Co-reporter:Xiang Wang, Jingfang Wang, Hanjun Cheng, Ping Yu, Jianshan Ye, and Lanqun Mao

Langmuir 2011 Volume 27(Issue 17) pp:11180-11186

Publication Date(Web):July 27, 2011

DOI:10.1021/la202018r

This study demonstrates the capability of graphene as a spacer to form electrochemically functionalized multilayered nanostructures onto electrodes in a controllable manner through layer-by-layer (LBL) chemistry. Methylene green (MG) and positively charged methylimidazolium-functionalized multiwalled carbon nanotubes (MWNTs) were used as examples of electroactive species and electrochemically useful components for the assembly, respectively. By using graphene as the spacer, the multilayered nanostructures of graphene/MG and graphene/MWNT could be readily formed onto electrodes with the LBL method on the basis of the electrostatic and/or π–π interaction(s) between graphene and the electrochemically useful components. Scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–vis), and cyclic voltammetry (CV) were used to characterize the assembly processes, and the results revealed that nanostructure assembly was uniform and effective with graphene as the spacer. Electrochemical studies demonstrate that the assembled nanostructures possess excellent electrochemical properties and electrocatalytic activity toward the oxidation of NADH and could thus be used as electronic transducers for bioelectronic devices. This potential was further demonstrated by using an alcohol dehydrogenase-based electrochemical biosensor and glucose dehydrogenase-based glucose/O2 biofuel cell as typical examples. This study offers a simple route to the controllable formation of graphene-based electrochemically functionalized nanostructures that can be used for the development of molecular bioelectronic devices such as biosensors and biofuel cells.

Bioelectrochemically Active Infinite Coordination Polymer Nanoparticles: One-Pot Synthesis and Biosensing Property

Co-reporter:Pengcheng Huang;Junjie Mao;Dr. Lifen Yang;Ping Yu; Lanqun Mao

Chemistry - A European Journal 2011 Volume 17( Issue 41) pp:11390-11393

Publication Date(Web):

DOI:10.1002/chem.201101634

Development of a dehydrogenase-based glucose anode using a molecular assembly composed of nile blue and functionalized SWCNTs and its applications to a glucose sensor and glucose/O2 biofuel cell

Co-reporter:Farhana S. Saleh, Lanqun Mao, Takeo Ohsaka

Sensors and Actuators B: Chemical 2011 Volume 152(Issue 1) pp:130-135

Publication Date(Web):20 February 2011

DOI:10.1016/j.snb.2010.07.054

A simple and new way to immobilize glucose dehydrogenase (GDH) enzyme onto nile blue (NB) covalently assembled on the surface of functionalized single-walled carbon nanotubes (f-SWCNTs) modified glassy carbon (GC) electrode (GDH/NB/f-SWCNTs/GC electrode) was described. The GDH/NB/f-SWCNTs/GC electrode possesses promising characteristics as glucose sensor; a wide linear dynamic range of 100–1700 μM, low detection limit of 0.3 μM, fast response time (1–2 s), high sensitivity (14 μA cm−2 mM−1), anti-interference ability and anti-fouling. Moreover, the performance of the GDH/NB/f-SWCNTs/GC bioanode was successfully tested in a glucose/O2 biofuel cell. The maximum power density delivered by the assembled glucose/O2 biofuel cell could reach 32.0 μW cm−2 at a cell voltage of 0.35 V with 40 mM glucose. The present procedure can be applied for preparing a potential platform to immobilize different enzymes for various bioelectrochemical applications.

Potential-controllable green synthesis and deposition of metal nanoparticles with electrochemical method

Co-reporter:Ping Yu, Qin Qian, Xiang Wang, Hanjun Cheng, Takeo Ohsaka and Lanqun Mao

Journal of Materials Chemistry A 2010 vol. 20(Issue 28) pp:5820-5822

Publication Date(Web):17 Jun 2010

DOI:10.1039/C0JM01293A

A controllable and environmentally friendly electrochemical method for task specific synthesis and deposition of metal nanoparticles was first demonstrated by simply adjusting the potentials for the reduction of metal precursors in ionic liquids.

Online Electrochemical Measurements of Ca2+ and Mg2+ in Rat Brain Based on Divalent Cation Enhancement toward Electrocatalytic NADH Oxidation

Co-reporter:Zipin Zhang, Lingzhi Zhao, Yuqing Lin, Ping Yu, and Lanqun Mao

Analytical Chemistry 2010 Volume 82(Issue 23) pp:9885

Publication Date(Web):November 8, 2010

DOI:10.1021/ac102605n

This study describes a novel electrochemical approach to effective online monitoring of electroinactive Ca2+ and Mg2+ in the rat brain based on the current enhancement of divalent cations toward electrocatalytic oxidation of NADH. Cyclic voltammetry for NADH oxidation at the electrodes modified with the polymerized film of toluidine blue O (TBO) reveals that the current of such an electrocatalytic oxidation process is remarkably enhanced by divalent cations such as Ca2+ and Mg2+. The current enhancement is thus used to constitute an electrochemical method for the measurements of Ca2+ and Mg2+ in a continuous-flow system with the polyTBO-modified electrode as the detector. Upon being integrated with in vivo microdialysis, the electrochemical method is successfully applied in investigating on cerebral Ca2+ and Mg2+ of living animals in two aspects: (1) online simultaneous measurements of the basal levels of Ca2+ and Mg2+ in the brain of the freely moving rats by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca2+ to differentiate the net current responses selectively for Ca2+ and Mg2+; and (2) online continuous monitoring of the cerebral Mg2+ following the global ischemia by using Ca2+-masking agent (i.e., EGTA) to completely eliminate the interference from Ca2+. Compared with the existing methods for the measurements of cerebral Ca2+ and Mg2+, the method demonstrated here is advantageous in terms of its simplicity both in instrumentation and in the experimental procedures and near real-time nature, and is thus highly anticipated to find wide applications in understanding of chemical events involved in some physiological and pathological processes.

Colorimetric Detection of Glucose in Rat Brain Using Gold Nanoparticles

Co-reporter:Ying Jiang;Hong Zhao Dr.;Yuqing Lin Dr.;Ningning Zhu Dr.;Yurong Ma

Angewandte Chemie International Edition 2010 Volume 49( Issue 28) pp:4800-4804

Publication Date(Web):

DOI:10.1002/anie.201001057

Colorimetric Detection of Glucose in Rat Brain Using Gold Nanoparticles

Co-reporter:Ying Jiang;Hong Zhao Dr.;Yuqing Lin Dr.;Ningning Zhu Dr.;Yurong Ma

Angewandte Chemie 2010 Volume 122( Issue 28) pp:4910-4914

Publication Date(Web):

DOI:10.1002/ange.201001057

Noncovalent Attachment of NAD+ Cofactor onto Carbon Nanotubes for Preparation of Integrated Dehydrogenase-Based Electrochemical Biosensors

Co-reporter:Haojie Zhou, Zipin Zhang, Ping Yu, Lei Su, Takeo Ohsaka and Lanqun Mao

Langmuir 2010 Volume 26(Issue 8) pp:6028-6032

Publication Date(Web):February 1, 2010

DOI:10.1021/la903799n

This study describes a facile approach to the preparation of integrated dehydrogenase-based electrochemical biosensors through noncovalent attachment of an oxidized form of β-nicotinamide adenine dinucleotide (NAD+) onto carbon nanotubes with the interaction between the adenine subunit in NAD+ molecules and multiwalled carbon nanotubes (MWCNTs). X-ray photoelectron spectroscopic and cyclic voltammetric results suggest that NAD+ is noncovalently attached onto MWCNTs to form an NAD+/MWCNT composite that acts as the electronic transducer for the integrated dehydrogenase-based electrochemical biosensors. With glucose dehydrogenase (GDH) as a model dehydrogenase-based recognition unit, electrochemical studies reveal that glucose is readily oxidized at the GDH/NAD+/MWCNT-modified electrode without addition of NAD+ in the phosphate buffer. The potential for the oxidation of glucose at the GDH/NAD+/MWCNT-modified electrode remains very close to that for NADH oxidation at the MWCNT-modified electrode, but it is more negative than those for the oxidation of glucose at the MWCNT-modified electrode and for NADH oxidation at a bare glassy carbon electrode. These results demonstrate that NAD+ molecules stably attached onto MWCNTs efficiently act as the cofactor for the dehydrogenases. MWCNTs employed here not only serve as the electronic transducer and the support to confine NAD+ cofactor onto the electrode surface, but also act as the electrocatalyst for NADH oxidation in the dehydrogenase-based electrochemical biosensors. At the GDH/NAD+/MWCNT-based glucose biosensor, the current is linear with the concentration of glucose being within a concentration range from 10 to 300 μM with a limit of detection down to 4.81 μM (S/N = 3). This study offers a facile and versatile approach to the development of integrated dehydrogenase-based electrochemical devices, such as electrochemical biosensors and biofuel cells.

Pt−Ru/CeO2/Carbon Nanotube Nanocomposites: An Efficient Electrocatalyst for Direct Methanol Fuel Cells

Co-reporter:Zhenyu Sun, Xiang Wang, Zhimin Liu, Hongye Zhang, Ping Yu and Lanqun Mao

Langmuir 2010 Volume 26(Issue 14) pp:12383-12389

Publication Date(Web):May 20, 2010

DOI:10.1021/la101060s

Pt−Ru/CeO2/multiwalled carbon nanotube (MWNT) electrocatalysts were prepared using a rapid sonication-facilitated deposition method and were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. Morphological characterization by TEM revealed that CeO2 nanoparticles (NPs) were in intimate contact with Pt−Ru NPs, and both were highly dispersed on the exteriors of nanotubes with a small size and a very narrow size distribution. Compared with the Pt−Ru/MWNT and Pt/MWNT electrocatalysts, the as-prepared Pt−Ru/CeO2/MWNT exhibited a significantly improved electrochemically active surface area (ECSA) and a remarkably enhanced activity toward methanol oxidation. The effects of the Pt−Ru loading and the Pt-to-Ru molar ratio on the electrocatalytic activity of Pt−Ru/CeO2/MWNT for methanol oxidation were investigated. We found that a maximum activity toward methanol oxidation reached at the 10 wt % of Pt−Ru loading and 1:1 of Pt-to-Ru ratio. Moreover, the role of CeO2 in the catalysts for the enhancement of methanol oxidation was discussed in terms of both bifunctional mechanism and electronic effects.

Sensitive impedimetric DNA biosensor with poly(amidoamine) dendrimer covalently attached onto carbon nanotube electronic transducers as the tether for surface confinement of probe DNA

Co-reporter:Ningning Zhu, Huan Gao, Qin Xu, Yuqing Lin, Lei Su, Lanqun Mao

Biosensors and Bioelectronics 2010 Volume 25(Issue 6) pp:1498-1503

Publication Date(Web):15 February 2010

DOI:10.1016/j.bios.2009.11.006

This study demonstrates a new impedimetric DNA biosensor with second-generation poly(amidoamine) dendrimer (G2-PAMAM) covalently functionalized onto multi-walled carbon nanotube (MWNT) electronic transducers as the tether for surface confinement of probe DNA. G2-PAMAM dendrimer was covalently functionalized onto purified MWNTs and the as-formed G2-PAMAM-functionalized MWNT composite (i.e., G2-PAMAM/MWNT) was used both as the support to confine the single-stranded DNA (ssDNA) probe and as the electronic transducer to form the DNA biosensors. Upon the occurrence of hybridization events between surface-confined ssDNA probe with target DNA in solution to form a double-stranded DNA (dsDNA) at electrode surface, the negative charge in the electrode/electrolyte interface and, as such, the interfacial charge-transfer resistance of the electrodes towards the Fe(CN)63−/4− redox couple were changed. Such a change was used for the impedimetric DNA biosensing. The use of G2-PAMAM dendrimer attached onto MWNT electronic transducer as the tether for probe DNA provides a large number of amino groups to increase the surface binding of probe DNA, results in the increase the sensitivity of the impedimetric biosensor for the target DNA. Under the conditions employed here, the change in the interfacial charge-transfer resistance was linear with the logarithm of the concentration of the target DNA within a concentration range from 0.5 to 500 pM with a detection limit of 0.1 pM (S/N = 3). The excellent analytical properties of the impedimetric DNA biosensors developed here substantially makes them potentially useful for practical applications.

A non-oxidative electrochemical approach to online measurements of dopamine release through laccase-catalyzed oxidation and intramolecular cyclization of dopamine

Co-reporter:Yuqing Lin, Zipin Zhang, Lingzhi Zhao, Xiang Wang, Ping Yu, Lei Su, Lanqun Mao

Biosensors and Bioelectronics 2010 Volume 25(Issue 6) pp:1350-1355

Publication Date(Web):15 February 2010

DOI:10.1016/j.bios.2009.10.028

A new electrochemical approach to selective online measurements of dopamine (DA) release in the cerebral microdialysate is demonstrated with a non-oxidative mechanism based on the distinct reaction properties of DA and the excellent biocatalytic activity of laccase. To make the successful transition of the distinct sequential reaction properties of DA from a conceptual determination protocol to a practical online analytical system, laccase enzyme is immobilized onto magnetite nanoparticles and the nanoparticles are confined into a fused-silica capillary through an external magnetic field to fabricate a magnetic microreactor. The microreactor is placed in the upstream of the thin-layer electrochemical flow cell to efficiently catalyze the oxidation of DA into its quinonoid form and thereby initialize the sequential reactions including deprotonation, intramolecular cyclization, disproportionation and/or oxidation to finally give 5,6-dihydroxyindoline quinone. The electrochemical reduction of the produced 5,6-dihydroxyindoline quinone at bare glassy carbon electrode is used as the readout for the DA measurement. The laccase-immobilized microreactor is also found to catalyze the oxidation of ascorbic acid (AA) and 3,4-dihydroxyphenylacetic acid (DOPAC) into electroinactive species and, as such, to eliminate the great interference from both species. Moreover, the successful transition of the mechanism for DA detection from the conventional oxidative electrochemical approach to the non-oxidative one substantially enables the measurements virtually interference-free from physiological levels of uric acid, 5-hydroxytryptamine, norepinephrine, and epinephrine. The current response is linear with DA concentration within a concentration range from 1 to 20 μM with a sensitivity of 3.97 nA/μM. The detection limit, based on a signal-to-noise ratio of 3, is calculated to be 0.3 μM. The high selectivity and the good linearity as well as the high stability of the online method make it very potential for continuous monitoring of cerebral DA release in physiological and pathological processes.

Effective Electrochemical Method for Investigation of Hemoglobin Unfolding Based on the Redox Property of Heme Groups at Glassy Carbon Electrodes

Co-reporter:Xianchan Li, Wei Zheng, Limin Zhang, Ping Yu, Yuqing Lin, Lei Su and Lanqun Mao

Analytical Chemistry 2009 Volume 81(Issue 20) pp:8557

Publication Date(Web):September 16, 2009

DOI:10.1021/ac9015215

This study demonstrates a facile and effective electrochemical method for investigation of hemoglobin (Hb) unfolding based on the electrochemical redox property of heme groups in Hb at bare glassy carbon (GC) electrodes. In the native state, the heme groups are deeply buried in the hydrophobic pockets of Hb with a five-coordinate high-spin complex and thus show a poor electrochemical property at bare GC electrodes. Upon the unfolding of Hb induced by the denaturant of guanidine hydrochloride (GdnHCl), the fifth coordinative bond between the heme groups and the residue of the polypeptides (His-F8) is broken, and as a result, the heme groups initially buried deeply in the hydrophobic pockets dissociate from the polypeptide chains and are reduced electrochemically at GC electrodes, which can be used to probe the unfolding of Hb. The results on the GdnHCl-induced Hb unfolding obtained with the electrochemical method described here well coincide with those studied with other methods, such as UV−vis spectroscopy, fluorescence, and circular dichroism. The application of the as-established electrochemical method is illustrated to study the kinetics of GdnHCl-induced Hb unfolding, the GdnHCl-induced unfolding of another kind of hemoprotein, catalase, and the pH-induced Hb unfolding/refolding.

Physiologically Relevant Online Electrochemical Method for Continuous and Simultaneous Monitoring of Striatum Glucose and Lactate Following Global Cerebral Ischemia/Reperfusion

Co-reporter:Yuqing Lin, Ningning Zhu, Ping Yu, Lei Su and Lanqun Mao

Analytical Chemistry 2009 Volume 81(Issue 6) pp:2067

Publication Date(Web):February 19, 2009

DOI:10.1021/ac801946s

This study demonstrates a new electroanalytical method with a high physiological relevance for simultaneous online monitoring of glucose and lactate in the striatum of the rat brain following global cerebral ischemia/reperfusion. The online analytical method is based on the efficient integration of in vivo microdialysis sampling with an online selective electrochemical detection with the electrochemical biosensors with dehydrogenases, i.e., glucose and lactate dehydrogenases, as recognition elements. The dehydrogenase-based electrochemical biosensors are developed onto the dual split-disk plastic carbon film (SPCF) electrodes with methylene green (MG) adsorbed onto single-walled carbon nanotubes (SWNTs) as the electrocatalyst for the oxidation of dihydronicotiamide adenine dinucleotide (NADH) at a low potential of 0.0 V (vs Ag/AgCl). Artificial cerebrospinal fluid (aCSF) containing NAD+ is externally perfused from a second pump and online mixed with the brain microdialysates to minimize the variation of pH that occurred following the cerebral ischemia/reperfusion and to supply NAD+ cofactor and O2 for the enzymatic reactions of dehydrogenases and ascorbate oxidase, respectively. As a result, the developed online electroanalytical method exhibits a high selectivity against the electrochemically active species endogenously existing in the cerebral systems and a high tolerance against the variation of pH and O2 following cerebral ischemia/reperfusion. This property, along with the good linearity and a high stability toward glucose and lactate as well as little cross-talk between two biosensors, substantially makes this method possible for the continuous, simultaneous, and online monitoring of glucose and lactate in the rat brain following global cerebral ischemia/reperfusion. This study establishes a new and effective platform for the investigation of the energy metabolism in physiological and pathological processes.

A facile method for preparation of graphene film electrodes with tailor-made dimensions with Vaseline as the insulating binder

Co-reporter:Shunlong Yang, Deyin Guo, Lei Su, Ping Yu, Dan Li, Jianshan Ye, Lanqun Mao

Electrochemistry Communications 2009 Volume 11(Issue 10) pp:1912-1915

Publication Date(Web):October 2009

DOI:10.1016/j.elecom.2009.08.020

This communication describes a facile but effective method to prepare graphene film electrodes with tunable dimensions with Vaseline as the insulating binder. Cyclic voltammetry (CV) studies reveal that the as-prepared graphene film electrodes have tunable dimensions ranging from a conventional electrode to a nanoelectrode ensemble, depending on the amount of graphene dispersed into the insulting Vaseline matrix. A large amount of graphene (typically, 10.0 μg/mL) leads to the formation of the film electrodes with a conventional dimension, while a small amount of graphene (typically, 1.0 μg/mL) essentially yields the graphene film electrodes like a nanoelectrode ensemble. As one new kind of carbon-based film electrodes with tailor-made dimensions and a good electrochemical activity as well as a high stability, the graphene film electrodes are believed to be potentially useful for fundamental electrochemical studies and for practical applications.

Comparative studies on electrochemical activity of graphene nanosheets and carbon nanotubes

Co-reporter:Jingfang Wang, Shunlong Yang, Deyin Guo, Ping Yu, Dan Li, Jianshan Ye, Lanqun Mao

Electrochemistry Communications 2009 Volume 11(Issue 10) pp:1892-1895

Publication Date(Web):October 2009

DOI:10.1016/j.elecom.2009.08.019

This study compares the electrochemical activity of four kinds of carbon materials, i.e. single-walled carbon nanotubes (SWNTs), pristine graphene oxide nanosheets (GONs), chemically reduced GONs, and electrochemically reduced GONs, with potassium ferricyanide (K3Fe(CN)6), β-nicotinamide adenine dinucleotide (NADH) and ascorbic acid (AA) as the redox probes. Cyclic voltammetry (CV) results demonstrate that the electron transfer kinetics of the redox probes employed here at the carbon materials essentially depend on the kind of the materials, of which the redox processes of the probes at SWNTs and electrochemically reduced GONs are faster than those at the pristine and chemically reduced GONs. The different electron transfer kinetics for the redox probes at the carbon materials studied here could be possibly ascribed to the synergetic effects of the surface chemistry (e.g., C/O ratio, presence of quinone-like groups, surface charge, and surface cleanness) and conductivity of the materials. This study could be potentially useful for understanding the structure/property relationship of the carbon materials and, based on this, for screening and synthesizing advanced carbon materials for electrochemical applications.

A facile approach to construction of a stable water-miscible ionic liquid/electrolyte interface with interactions between imidazolium moiety and carbon nanotubes

Co-reporter:Ping Yu, Heng Zhou, Ningning Zhu, Yuqing Lin, Lanqun Mao

Electrochemistry Communications 2009 Volume 11(Issue 7) pp:1393-1396

Publication Date(Web):July 2009

DOI:10.1016/j.elecom.2009.05.014

A stable water-miscible ionic imidazolium-based ionic liquid/electrolyte interface is constructed in aqueous media based on the interaction between the imidazolium moiety in ionic liquids (ILs) and single-walled carbon nanotubes (SWNTs). 1-n-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) is used as one kind of typical water-miscible ILs for this study. The nanocomposite of IL and SWNTs is prepared by dispensing SWNTs into IL and the as-prepared nanocomposite is confined onto glassy carbon (GC) electrodes to construct the IL/electrolyte interface. X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and cyclic voltammetry (CV) results demonstrate that the imidazolium moiety in ILs could interact with SWNTs to form a stable nanocomposite possibly through π-cation or other kinds of interactions between both components. CV results with Fe(CN)64-/3- redox probe suggest the electrochemical interfacial is relatively stable in the aqueous media with a fast electron transfer property. This study may be useful both for the fundamental electrochemical studies and for the practical applications associated with the water-miscible imidazolium-based ILs.

Voltammetric determination of water with inner potential reference and variable linear range based on structure- and redox-controllable hydrogen-bonding interaction between water and quinones

Co-reporter:Limin Zhang, Haojie Zhou, Xianchan Li, Yuqing Lin, Ping Yu, Lei Su, Lanqun Mao

Electrochemistry Communications 2009 Volume 11(Issue 4) pp:808-811

Publication Date(Web):April 2009

DOI:10.1016/j.elecom.2009.01.037

This communication describes a new voltammetric method for the determination of water in nonaqueous solvent by taking advantage of the structure- and redox-controllable hydrogen-bonding interaction between quinone species and water. Three kinds of quinones, i.e., tetrachloro-p-benzoquinone (TCBQ), benzoquinone (BQ), and tetramethyl-p-benzoquinone (TMBQ), are employed in this study in terms of their different structures and thereby different basicities and hydrogen-bonding interaction activities with water. The hydrogen-bonding interaction activities of the quinone species with water actually depend on the structures and the species of quinones, where the interaction activity between quinone dianion and water remains remarkably greater than that between quinone monoanion and water. The former interaction activity eventually leads to the positive shift of the half-wave potential of quinone monoanion/dianion couple, which can be essentially used for the voltammetric determination of water. The structure- and redox-controllable hydrogen-bonding interaction activities of quinones and water substantially make it possible to determine trace amount of water in the nonaqueous solution with inner reference potential and variable dynamic linear range.

Doping polyaniline with pristine carbon nanotubes into electroactive nanocomposite in neutral and alkaline media

Co-reporter:Haojie Zhou, Yuqing Lin, Ping Yu, Lei Su, Lanqun Mao

Electrochemistry Communications 2009 Volume 11(Issue 5) pp:965-968

Publication Date(Web):May 2009

DOI:10.1016/j.elecom.2009.02.036

This study describes a facile but effective route to synthesis of electroactive polyaniline (PANI) in the neutral and alkaline media simply with pristine single-walled carbon nanotubes (SWNTs) as the dopant. Cyclic voltammetry (CV) studies reveal that the SWNT/PANI nanocomposite processes a good electrochemical activity in the neutral and alkaline media. Control experiments with PANI mixed with heat-treated SWNTs imply that the electrochemical properties of the SWNT/PANI nanocomposite in the neutral and alkaline media do not result from the presence of carboxylic groups at SWNTs themselves, and in turn show that the pristine SWNTs can be potentially used as a new and effective dopant to preserve the electrochemical property of PANI in the neutral and alkaline media. This property of the SWNT/PANI nanocomposite is reasonably envisaged to be promising for electrochemical investigations and electroanalytical applications, especially for the development of electrochemical sensors, biosensors and biofuel cells.

Label-free and sequence-specific DNA detection down to a picomolar level with carbon nanotubes as support for probe DNA

Co-reporter:Ningning Zhu, Yuqing Lin, Ping Yu, Lei Su, Lanqun Mao

Analytica Chimica Acta 2009 Volume 650(Issue 1) pp:44-48

Publication Date(Web):14 September 2009

DOI:10.1016/j.aca.2009.05.017

This study describes a simple and label-free electrochemical impedance spectroscopic (EIS) method for sequence-specific detection of DNA by using single-walled carbon nanotubes (SWNTs) as the support for probe DNA. SWNTs are confined onto gold electrodes with mixed self-assembly monolayers of thioethanol and cysteamine. Single-stranded DNA (ssDNA) probe is anchored onto the SWNT support through covalent binding between carboxyl groups at the nanotubes and amino groups at 5′ ends of ssDNA. Hybridization of target DNA with the anchored probe DNA greatly increases the interfacial electron-transfer resistance (Ret) at the double-stranded DNA (dsDNA)-modified electrodes for the redox couple of Fe(CN)63−/4−, which could be used for label-free and sequence-specific DNA detection. EIS results demonstrate that the utilization of SWNTs as the support for probe DNA substantially increases the surface loading of probe DNA onto electrode surface and thus remarkably lowers the detection limit for target DNA. Under the conditions employed here, Ret is linear with the concentration of target DNA within a concentration range from 1 to 10 pM with a detection limit down to 0.8 pM (S/N = 3). This study may offer a novel and label-free electrochemical approach to sensitive sequence-specific DNA detection.

Electrochemical sensing of ATP with synthetic cyclophane as recognition element

Co-reporter:YuRong Ma;Hong Zhao;Ping Yu;Lei Su;DeQing Zhang

Science China Chemistry 2009 Volume 52( Issue 6) pp:741-745

Publication Date(Web):2009 June

DOI:10.1007/s11426-009-0074-3

A new electrochemical sensor for ATP with synthetic cyclophane stably attached onto single-walled carbon nanotubes (SWNTs) as the recognition elements is described. UV-vis and cyclic voltammetric results demonstrate that ATP may interact with the synthetic cyclophane recognition elements to form a stable adduct mainly through electrostatic, π-π stacking and donor-acceptor interactions. Such interactions eventually lead to a decrease in the peak currents of the cyclophane recognition elements attached onto the SWNT electronic transducer, which could be used for electrochemical sensing of ATP. Under the conditions employed here, the ratio of the decrease in the anodic peak current is linear with ATP concentration within a concentration range from 10 to 120 μM with a linear coefficiency of 0.993. This study may offer a new and simple electrochemical approach for effective sensing of ATP.

On-line electrochemical measurements of cerebral hypoxanthine of freely moving rats

Co-reporter:ZiPin Zhang;YuQing Lin

Science China Chemistry 2009 Volume 52( Issue 10) pp:1677-1682

Publication Date(Web):2009 October

DOI:10.1007/s11426-009-0231-8

This study demonstrates an on-line method for continuous measurements of cerebral hypoxanthine in the freely moving rats with integration of selective electrochemical biosensing with in vivo microdialysis sampling. The selective electrochemical biosensing is achieved by using xanthine oxidase (XOD) as the specific sensing element and Prussian blue (PB) as the electrocatalyst for the reduction of H2O2 generated from the oxidase-catalyzed reaction. The method is virtually interference-free from the coexisting electroactive species in the brain and exhibits a good stability and reproducibility. Upon integrated with in vivo microdialysis, the on-line method is well suitable for continuous measurements of cerebral hypoxanthine of freely moving rats, which is illustrated by the measurements of the microdialysates after the hypoxanthine standard was externally infused into the rat brain. This study essentially offers a facile on-line electrochemical approach to continuous measurements of cerebral hypoxanthine and could find some interesting applications in physiological and pathological investigations associated with hypoxanthine.

Rational Functionalization of Carbon Nanotubes Leading to Electrochemical Devices with Striking Applications

Co-reporter:Jie Yan;Haojie Zhou;Ping Yu;Lei Su

Advanced Materials 2008 Volume 20( Issue 15) pp:2899-2906

Publication Date(Web):

DOI:10.1002/adma.200800674

Abstract

As one-dimensional carbon nanostructures, carbon nanotubes (CNTs) are a member of the carbon family but they possess very different structural and electronic properties from other kinds of carbon materials frequently used in electrochemistry, such as glassy carbon, graphite, and diamond. Although the past decade has witnessed rapid and substantial progress in both the fundamental understanding of CNT-oriented electrochemistry and the development of various kinds of electrochemical devices with carbon nanotubes, the increasing demand from both academia and industry requires CNT-based electrochemical devices with vastly improved properties, such as good reliability and durability, and high performance. As we outline here, the smart functionalization of CNTs and effective methods for the preparation of devices would pave the way to CNT-based electronic devices with striking applications.

An electrochemical sensor for 3,4-dihydroxyphenylacetic acid with carbon nanotubes as electronic transducer and synthetic cyclophane as recognition element

Co-reporter:Jie Yan, Yucheng Zhou, Ping Yu, Lei Su, Lanqun Mao, Deqing Zhang and Daoben Zhu

Chemical Communications 2008 (Issue 36) pp:4330-4332

Publication Date(Web):17 Jul 2008

DOI:10.1039/B805958F

A new electrochemical sensor was demonstrated for selective sensing of 3,4-dihydroxyphenylacetic acid (DOPAC) through a non-oxidative mechanism by using single-walled carbon nanotubes (SWNTs) as the electronic transducer and a synthetic cyclophane electron acceptor as the recognition element.

In Situ Cationic Ring-Opening Polymerization and Quaternization Reactions To Confine Ferricyanide onto Carbon Nanotubes: A General Approach to Development of Integrative Nanostructured Electrochemical Biosensors

Co-reporter:Ling Xiang, Zhinan Zhang, Ping Yu, Jun Zhang, Lei Su, Takeo Ohsaka and Lanqun Mao

Analytical Chemistry 2008 Volume 80(Issue 17) pp:6587

Publication Date(Web):August 1, 2008

DOI:10.1021/ac800733t

This study demonstrates a new and relatively general route to the development of multiwalled carbon nanotube (MWNT)-based integrative electrochemical biosensors by confining ferricyanide redox mediator onto MWNTs. The ferricyanide-confined MWNTs are synthesized first through grafting of epoxy chloropropane onto MWNTs with in situ cationic ring-opening polymerization and then introducing the positively charged methylimidazolium moieties into the grafted polymer with a quaternization reaction. The grafted polymers with positively charged methylimidazolium moieties tethered onto MWNTs can essentially be used to confine redox-active ferricyanide onto MWNTs to form a redox mediator-confined nanocomposite with a good stability and excellent electrochemical property. The synthetic nanocomposite with surface-confined ferricyanide is demonstrated to be well-competent as the efficient electronic transducers for the general development of electrochemical biosensors upon combination with biorecognition units, which is illustrated by using glucose oxidase and laccase as two model biorecognition units. This study essentially paves a facile and general approach to the development of integrative nanostructured electrochemical biosensors.

A Miniature glucose/O2 biofuel cell with single-walled carbon nanotubes-modified carbon fiber microelectrodes as the substrate

Co-reporter:Xianchan Li, Haojie Zhou, Ping Yu, Lei Su, Takeo Ohsaka, Lanqun Mao

Electrochemistry Communications 2008 Volume 10(Issue 6) pp:851-854

Publication Date(Web):June 2008

DOI:10.1016/j.elecom.2008.03.019

This study demonstrates a new kind of miniature glucose/O2 biofuel cells (BFCs) based on carbon fiber microelectrodes (CFMEs) modified with single-walled carbon nanotubes (SWNTs). SWNTs are used as a support both for stably confining the electrocatalyst (i.e., methylene green, MG) for the oxidation of NADH and the anodic biocatalyst (i.e., NAD+-dependent glucose dehydrogenase, GDH) for the oxidation of glucose and for efficiently facilitating direct electrochemistry of the cathodic biocatalyst (i.e., laccase) for the O2 reduction. The prepared micro-sized GDH-based bioanode and laccase-based biocathode exhibit good bioelectrocatalytic activity toward the oxidation of glucose and the reduction of oxygen, respectively. In 0.10 M phosphate buffer containing 10 mM NAD+ and 45 mM glucose under ambient air, the power density of the assembled miniature compartment-less glucose/O2 BFC reaches 58 μW cm−2 at 0.40 V. The stability of the miniature glucose/O2 BFC is also evaluated.

Aptamer-based electrochemical sensors that are not based on the target binding-induced conformational change of aptamers

Co-reporter:Ying Lu, Ningning Zhu, Ping Yu and Lanqun Mao

Analyst 2008 vol. 133(Issue 9) pp:1256-1260

Publication Date(Web):28 Jul 2008

DOI:10.1039/B807913G

This study describes a new kind of aptamer-based electrochemical sensor that is not based on the target binding-induced conformational change of the aptamers by using a 15-mer thrombin-binding aptamer (5′-GGTTGGTGTGGTTGG-3′) as the model oligonucleotide. The sensors are developed by first self-assembling the aptamer (i.e. a thrombin-binding aptamer) onto an Au electrode and then hybridizing the assembled aptamer with a ferrocene (Fc)-labeled short aptamer-complementary DNA oligonucleotide to form an electroactive double-stranded DNA (ds-DNA) oligonucleotide onto the Au electrode. The binding of the target (i.e. thrombin) towards the aptamer essentially destroys the Watson–Crick helix structure of the ds-DNA oligonucleotide assembled onto the electrode and leads to the dissociation of the Fc-labeled short complementary DNA oligonucleotide from the electrode surface to the solution, resulting in a decrease in the current signal obtained at the electrode, which can be used for the determination of the target. With the thrombin-binding aptamer as the model oligonucleotide, the current decrease obtained with the aptamer-based electrochemical sensors is linear with the concentration of thrombin within the concentration range from 0 to 10 nM (ΔI/nA = 6.7Cthrombin/nM + 2.8, γ = 0.975). Unlike most kinds of existing aptamer-based electrochemical sensor, the electrochemical aptasensors demonstrated here are not based on the conformational change of the aptamers induced by the specific target binding. Moreover, the aptasensors are essentially label-free and are very responsive toward the targets. This study may pave a facile and general way to the development of aptamer-based electrochemical sensors.

A Simple Assay for Direct Colorimetric Visualization of Trinitrotoluene at Picomolar Levels Using Gold Nanoparticles

Co-reporter:Ying Jiang;Hong Zhao Dr.;Ningning Zhu Dr.;Yuqing Lin Dr.;Ping Yu Dr.

Angewandte Chemie 2008 Volume 120( Issue 45) pp:8729-8732

Publication Date(Web):

DOI:10.1002/ange.200804066

A Simple Assay for Direct Colorimetric Visualization of Trinitrotoluene at Picomolar Levels Using Gold Nanoparticles

Co-reporter:Ying Jiang;Hong Zhao Dr.;Ningning Zhu Dr.;Yuqing Lin Dr.;Ping Yu Dr.

Angewandte Chemie International Edition 2008 Volume 47( Issue 45) pp:8601-8604

Publication Date(Web):

DOI:10.1002/anie.200804066

An enzymatic glucose/O2 biofuel cell: Preparation, characterization and performance in serum

Co-reporter:Feng Gao, Yiming Yan, Lei Su, Lun Wang, Lanqun Mao

Electrochemistry Communications 2007 Volume 9(Issue 5) pp:989-996

Publication Date(Web):May 2007

DOI:10.1016/j.elecom.2006.12.008

This study demonstrates a new kind of single-walled carbon nanotubes (SWNT)-based compartment-less glucose/O2 biofuel cell (BFC) with glucose dehydrogenase (GDH) and bilirubin oxidase (BOD) as the anodic and cathodic biocatalysts, respectively, and with poly(brilliant creysl blue) (BCB) adsorbed onto SWNT nanocomposite as the electrocatalyst for the oxidation of NADH. The prepared GDH-polyBCB-SWNT bioanode exhibits an excellent electrocatalytic activity toward the oxidation of glucose biofuel; in 0.10 M phosphate buffer containing 20 mM NAD+ and 100 mM glucose, the oxidation of glucose commences at −0.25 V and the current reaches its maximum of 310 μA/cm2 at −0.05 V vs. Ag/AgCl. At the BOD-SWNT biocathode, a high potential output is achieved for the reduction of O2 due to the direct electron transfer property of BOD at the SWNTs. In 0.10 M phosphate buffer, the electrocatalytic reduction of O2 is observed at a high potential of 0.53 V vs. Ag/AgCl with an electrocatalytic current plateau of ca. 28 μA/cm2 at 0.45 V under ambient air and ca. 102 μA/cm2 under O2-saturated atmosphere. In 0.10 M phosphate buffer containing 10 mM NAD+ and 40 mM glucose under O2-saturated atmosphere, the power density of the assembled SWNT-based glucose/O2 BFC reaches 53.9 μW/cm2 at 0.50 V. The performance and the stability of the glucose/O2 BFC are also evaluated in serum. This study could offer a new route to the development of new kinds of enzymatic BFCs with a high performance and provide useful information on future studies on the enzymatic BFCs as in vivo power sources.

Carbon-Nanotube-Based Glucose/O2 Biofuel Cells

Co-reporter:Y. Yan;L. Su;W. Zheng;L. Mao

Advanced Materials 2006 Volume 18(Issue 19) pp:2639-2643

Publication Date(Web):26 SEP 2006

DOI:10.1002/adma.200600028

A single-walled carbon nanotube (SWNT)-based enzymatic glucose/O₂biofuel cell with a high voltage is demonstrated. The fuel cell uses glucose dehydrogenase as the anode biocatalyst for the oxidation of glucose, and laccase as the cathode biocatalyst for the reduction of O₂ (see figure). The SWNTs are used as electrode materials, as a support for electrocatalysts and biocatalysts, and for facilitating the direct electron transfer of laccase.

Comparative study of change in extracellular ascorbic acid in different brain ischemia/reperfusion models with in vivo microdialysis combined with on-line electrochemical detection

Co-reporter:Kun Liu, Yuqing Lin, Ling Xiang, Ping Yu, Lei Su, Lanqun Mao

Neurochemistry International (May 2008) Volume 52(Issue 6) pp:1247-1255

Publication Date(Web):1 May 2008

DOI:10.1016/j.neuint.2008.01.006

Information on the change in extracellular ascorbic acid (AA) during the acute period of cerebral ischemia is of great importance in the early therapeutic intervention of the cerebral ischemic injury since AA is known to be involved into most kinds of neurochemical changes in the cerebral ischemia. This study describes a fast and efficient method through integration of in vivo microdialysis with on-line electrochemical detection for continuous monitoring cerebral AA, allowing comparative study of the change in the extracellular AA level in different brain ischemia/reperfusion models. The method exhibits a high specificity for AA measurements, bearing a good tolerance against the fluctuation in the brain anoxia and acidity induced by cerebral ischemia/reperfusion. In the global two-vessel occlusion (2-VO) ischemia model, the striatum AA did not change with statistic significance until 60 min after occlusion and was decreased to be 91 ± 3% (n = 5, P < 0.05) of the basal level (8.05 ± 0.23 μM) at the time point of 60 min after occlusion. In the 2-VO ischemia/reperfusion model, AA remained unchanged during the 10 min of ischemia, and was sharply increased to be 267 ± 74% (n = 5, P < 0.05) of the basal level after the initial 15 min of reperfusion, and then decreased to be 122 ± 33% (n = 5, P < 0.05) of the basal level after 50 min of reperfusion. Extracellular AA was largely increased after 5 min of left middle cerebral artery occlusion (LMCAO) and was then gradually increased to be 257 ± 49% (n = 5, P < 0.05) of the basal level after 60 min of LMCAO ischemia. In the LMCAO ischemia/reperfusion model, AA was greatly increased during 10 min of ischemia and then gradually increased to be 309 ± 69% (n = 5, P < 0.05) of the basal level after the consecutive 50 min of reperfusion. The results demonstrated here may be useful for understanding the neurochemical processes in the acute period of cerebral ischemia and could thus be important for neuroprotective therapeutics for cerebral ischemic injury.

Graphdiyne oxide as a platform for fluorescence sensing

Co-reporter:Chunxia Wang, Ping Yu, Shuyue Guo, Lanqun Mao, Huibiao Liu and Yuliang Li

Chemical Communications 2016 - vol. 52(Issue 32) pp:NaN5632-5632

Publication Date(Web):2016/03/22

DOI:10.1039/C6CC01856D

An electrochemical sensor for 3,4-dihydroxyphenylacetic acid with carbon nanotubes as electronic transducer and synthetic cyclophane as recognition element

Co-reporter:Jie Yan, Yucheng Zhou, Ping Yu, Lei Su, Lanqun Mao, Deqing Zhang and Daoben Zhu

Chemical Communications 2008(Issue 36) pp:NaN4332-4332

Publication Date(Web):2008/07/17

DOI:10.1039/B805958F

Tuning interionic interaction for highly selective in vivo analysis

Co-reporter:Ping Yu, Xiulan He and Lanqun Mao