A simple one-step electrodeposition method was used to fabricate various gold nanostructures on glassy carbon electrodes in a low concentration of HAuCl4 solution (5 mM). The morphologies of final gold nanostructures can be easily controlled by varying the pH of the precursors or the deposition temperature. X-ray powder diffraction, scanning electronic microscopy, transmission electron microscopy, contact angle measurements, and electrochemical methods were used to characterize them. Hierarchical waxberry-like gold nanostructures with high active surface areas were obtained in pH 4 bath, and they had a higher catalytic performance for the reduction of oxygen than the other nanogold. These gold structures also displayed an extraordinary superhydrophobicity and the contact angle increased with the increase of deposition temperature and time. Their electrocatalytic response to the oxidation of glucose was also investigated. A sensitive enzyme-free sensor can be easily developed for the detection of glucose in pH 7.4 phosphate buffer solution.

Conformational fluctuations play a central role in the electron transfer reactions of molecules. Because the fluctuations can be extremely fast in kinetics and small in amplitude, a technique with fast temporal resolution and high conformational sensitivity is needed to follow the transient electron transfer processes. Here we report on an electrochemically controlled plasmonic detection technique capable of monitoring conformational changes in redox molecules with ns response time. Using the technique, we study the electron transfer reaction and the associated conformational gating of a redox protein (cytochrome c). The study reveals that the conformational gating takes place over a broad range of time scales, from microsecond to millisecond.

Sensitive photoelectrochemical (PEC) bioanalysis usually relies on enzyme-assisted signal amplification. This work describes the first proof-of-concept study for liposome-based PEC bioanalysis. Specifically, unilamellar liposomes were prepared and then utilized to carry the enediol-ligands and antibodies within their internal cavities and upon their external surfaces, respectively. On the other hand, the 96-well plate was used for accommodating the sandwich immunocomplexing, and then the confined liposomes were directed to release the encapsulated enediol-ligands into an individual well. The subsequent in situ sensitization of the TiO2 nanoparticles (NPs) electrode was then used to transduce the recognition events. This facile strategy allows for sensitive immunoassay without the involvement of laborious electrode fabrication and enzymatic amplification. Importantly, the protocol can be extended as a general PEC method for numerous other targets of interest. We believe this work could offer a new perspective for the rational implementation of various liposome complexes for novel PEC bioanalysis.

Targeted delivery of intracellular stimuli-activatable photosensitizers (PSs) into tumor cells to achieve selective imaging and on-demand photodynamic therapy (PDT) of tumors has provided a vital opportunity for precise cancer diagnosis and therapy. In this paper, we report a tumor targeting and adenosine triphosphate (ATP)-activatable nanophotosensitizer Apt-HyNP/BHQ2 by modifying hybrid micellar nanoparticles with both nucleolin-targeting aptamer AS1411 and quencher BHQ2-labeled ATP-binding aptamer BHQ2-ATP-apt. We demonstrated that both of the fluorescence emissions at 555 and 627 nm were quenched by BHQ2 in Apt-HyNP/BHQ2, resulting in low PDT capacity. After selective entry into tumor cells through nucleolin-mediated endocytosis, the high concentration of intracellular ATP could bind to BHQ2-ATP-apt and trigger Apt-HyNP/BHQ2 dissociation, leading to turning “on” both fluorescence and PDT. The “off–on” fluorescence emissions at both 555 and 627 nm were successfully applied for dual color fluorescence imaging of endogenous ATP levels and real-time monitoring of intracellular activation of Apt-HyNP/BHQ2 in tumor cells. Moreover, imaging-guided precise PDT of tumors in living mice was also demonstrated, allowing for selective ablation of tumors without obvious side effects. This study highlights the potential of using a combination of tumor-targeting and ATP-binding aptamers to design ATP-activatable PSs for both fluorescence imaging and imaging-guided PDT of tumors in vivo.

Single nanoparticle collisions have become popular for studying the electrochemical activity of single nanoparticles by determining the transient current during stochastic collisions with the electrode surface. However, if only the electrochemical current is measured, it remains challenging to identify and characterize the individual particle that is responsible for a specific current peak in a collision event; this hampers the understanding of the structure–activity relationship. Herein, we report simultaneous optical and electrochemical recording of a single nanoparticle collision; the electrochemical signal corresponds with the activity of a single nanoparticle, and the optical signal reveals the size and location of the same nanoparticle. Consequently, the structure (optical signal)–activity (electrochemical signal) relationship can be elucidated at the single nanoparticle level; this has implications for various applications including batteries, electrocatalysts, and electrochemical sensors. In addition, our previous studies have suggested an optical-to-electrochemical conversion model to independently calculate the electron transfer rate of single nanoparticles from the optical signal. The simultaneous optical and electrochemical recording achieved in the present work enables direct and quantitative validation of the optical-to-electrochemical conversion model.

Because graphene has nearly zero density of states at the Dirac point, charging it must overcome Pauli repulsion. We show here that this repulsion causes graphene to expand, which is measurable with an optical edge-tracking method despite that graphene is the strongest material. The expansion increases quadratically with applied voltage as predicted by theory and has a coefficient of ∼10–4 per V at 1 V. Graphene has many attractive properties, but it lacks piezoelectricity, which limits its electromechanical applications. The observed Pauli repulsion-induced expansion provides an alternative way to electrically control graphene dimension. It also provides a simple and direct method to measure the elastic properties of graphene and other low dimensional materials.Keywords: electromechanical properties of graphene; graphene expansion; Pauli repulsion; quantum capacitance; Young’s modulus of graphene;

Intracellular biothiols mediate many important physiological and pathological processes. Due to their low content and competing thiol-reactivity, it is still an unmet challenge to quantify them within a complicated intracellular environment. Herein, we demonstrated a strategy to discriminate three biothiols, i.e. cysteine (Cys), homo-cysteine (Hcy) and glutathione (GSH), and quantify their concentrations within single living cells, using one platform of Raman probe. By monitoring the reaction kinetics of biothiols with Raman probes and discriminating their products with a quantitative principal component analysis (qPCA) method, these three biothiols could be simultaneously quantified in both cell lysis and single living cells. The concentrations of Cys, Hcy and GSH in single Hela cells were 158 ± 19 μM, 546 ± 67 μM and 5.07 ± 0.62 mM, respectively, which gives the precise concentrations of these three biothiols at a single cell level for the first time. This method provides a general strategy for discriminating each component from a mixed system and has potential for quantifying any biomolecules within an in vitro or in vivo biological environment.

Semiconductor quantum dots (QDs) have served as superior optically active nanomaterials for molecular imaging and photodynamic therapy (PDT), but the low singlet oxygen (1O2) quantum yield and lack of tumor selectivity have limited their applications for tumor PDT in vivo. Here, we report the rational engineering of QDs into tumor-targeting hybrid nanoparticles through micelle-encapsulating a pre-assembled unique QD-Zn-porphyrin complex, a highly fluorescent organic photosensitizer rhodamine 6G (R6G), and a near-infrared fluorophore NIR775 with folic acid labeled phospholipid polymers. These nanoparticles have large porphyrin payloads and strong light absorption capability, thus contributing to an extremely high 1O2 quantum yield (∼0.91) via an efficient dual energy transfer process. In vivo studies show that they can preferably accumulate in tumors through folate receptor-mediated active delivery, permitting non-invasive fluorescence imaging and effective PDT of tumors in living mice. This study highlights the utility of hybrid semiconductor QDs for both tumor imaging and PDT in vivo.Rational engineering of semiconductor QDs into tumor targeting hybrid nanoparticles through micelle-encapsulating pre-assembled unique TMPyP-Zn-QD complexes, R6G and NIR775 with phospholipid polymers was demonstrated, enabling a dual energy transfer process to trigger remarkable 1O2 quantum yield (∼0.91) and a preferential accumulation in tumors for effective tumor PDT in living mice.Download high-res image (298KB)Download full-size image

Electrochemical reactions are involved in many natural phenomena, and are responsible for various applications, including energy conversion and storage, material processing and protection, and chemical detection and analysis. An electrochemical reaction is accompanied by electron transfer between a chemical species and an electrode. For this reason, it has been studied by measuring current, charge, or related electrical quantities. This approach has led to the development of various electrochemical methods, which have played an essential role in the understanding and applications of electrochemistry. While powerful, most of the traditional methods lack spatial and temporal resolutions desired for studying heterogeneous electrochemical reactions on electrode surfaces and in nanoscale materials. To overcome the limitations, scanning probe microscopes have been invented to map local electrochemical reactions with nanometer resolution. Examples include the scanning electrochemical microscope and scanning electrochemical cell microscope, which directly image local electrochemical reaction current using a scanning electrode or pipet. The use of a scanning probe in these microscopes provides high spatial resolution, but at the expense of temporal resolution and throughput.This Account discusses an alternative approach to study electrochemical reactions. Instead of measuring electron transfer electrically, it detects the accompanying changes in the reactant and product concentrations on the electrode surface optically via surface plasmon resonance (SPR). SPR is highly surface sensitive, and it provides quantitative information on the surface concentrations of reactants and products vs time and electrode potential, from which local reaction kinetics can be analyzed and quantified. The plasmonic approach allows imaging of local electrochemical reactions with high temporal resolution and sensitivity, making it attractive for studying electrochemical reactions in biological systems and nanoscale materials with high throughput.The plasmonic approach has two imaging modes: electrochemical current imaging and interfacial impedance imaging. The former images local electrochemical current associated with electrochemical reactions (faradic current), and the latter maps local interfacial impedance, including nonfaradic contributions (e.g., double layer charging). The plasmonic imaging technique can perform voltammetry (cyclic or square wave) in an analogous manner to the traditional electrochemical methods. It can also be integrated with bright field, dark field, and fluorescence imaging capabilities in one optical setup to provide additional capabilities. To date the plasmonic imaging technique has found various applications, including mapping of heterogeneous surface reactions, analysis of trace substances, detection of catalytic reactions, and measurement of graphene quantum capacitance. The plasmonic and other emerging optical imaging techniques (e.g., dark field and fluorescence microscopy), together with the scanning probe-based electrochemical imaging and single nanoparticle analysis techniques, provide new capabilities for one to study single nanoparticle electrochemistry with unprecedented spatial and temporal resolutions. In this Account, we focus on imaging of electrochemical reactions at single nanoparticles.

Ratiometric fluorescent sensors, which can provide built-in self-calibration for correction of a variety of analyte-independent factors, have attracted particular attention for analytical sensing and optical imaging with the potential to provide a precise and quantitative analysis. A wide variety of ratiometric sensing probes using small fluorescent molecules have been developed. Compared with organic dyes, exploiting semiconductor quantum dots (QDs) in ratiometric fluorescence sensing is even more intriguing, owing to their unique optical and photophysical properties that offer significant advantages over organic dyes. In this review, the main photophysical mechanism for generating dual-emission from QDs for ratiometry is discussed and categorized in detail. Typically, dual-emission can be obtained either with energy transfer from QDs to dyes or with independent dual fluorophores of QDs and dye/QDs. The recent discovery of intrinsic dual-emission from Mn-doped QDs offers new opportunities for ratiometric sensing. Particularly, the signal transduction of QDs is not restricted to fluorescence, and electrochemiluminescence and photoelectrochemistry from QDs are also promising for sensing, which can be made ratiometric for correction of interferences typically encountered in electrochemistry. All these unique photophysical properties of QDs lead to a new avenue of ratiometry, and the recent progress in this area is addressed and summarized here. Several interesting applications of QD-based ratiometry are presented for the determination of metal ions, temperature, and biomolecules, with specific emphasis on the design principles and photophysical mechanisms of these probes.

Facile and efficient detection of cancer cells at their preclinical stages is one of the central challenges in cancer diagnostics. A direct, rapid, highly sensitive and specific biosensor for detection of cancer biomarkers is desirable in early diagnosis and prognosis of cancer. In this work, we developed, for the first time, an easy and intuitive dispersion-dominated colorimetric strategy for cancer cell detection based on combining multi-DNA released from an aptamer scaffold with cyclic enzymatic amplification, which was triggered by aptamer DNA conformational switch and demonstrated by non-cross-linking gold nanoparticles (Au NPs) aggregation. First, five kinds of messenger DNAs (mDNAs) were aligned on the cancer cell aptamers modified on magnetic beads (MBs) to form mDNAs-Apt-MBs biocompatible nanosensors. In the presence of target cells, the aptamer would bind to the receptors on the cell membranes, and mDNAs would be released, resulting in the first amplification that one biological binding event would cause the release of multiple kinds of mDNAs simultaneously. After magnetic separation, the released mDNAs were introduced into the cyclic enzymatic amplification to cleave more single strand DNA (ssDNA) fragments. Instead of modification of Au NPs, these fragments and mDNAs could be adsorbed on the surface of Au NPs to prevent particle aggregation and ensure the stability and color of solution in high salt environments. The linear response for HL-60 cells in a concentration range from 10 to 104 cells was obtained with a detection limit of four cells in buffer solution. Moreover, the feasibility of the proposed strategy was demonstrated in a diluted serum sample. This dual signal amplification method can be extended to other types of cancer cells, which has potential application in point-of-care cancer diagnosis.Keywords: aptamer; cancer cells recognition; colorimetric detection; dual signal amplification; gold nanoparticles; magnetic nanoparticle

In this work, direct exciton–plasmon interactions (EPI) between CdS quantum dots (QDs) and Ag nanoparticles (NPs) were invoked ingeniously by catalytic Ag deposition on Au NPs for the stimulation of high efficient damping effect toward the excitonic responses in CdS QDs, on the basis of which a novel photoelectrochemical (PEC) bioanalytical format was achieved for sensitive microRNA detection. Specifically, upon the configurational change from the hairpin probe DNA to the “Y”-shaped ternary conjugate consisting of the original probe DNA, assistant DNA, and the target microRNA, the alkaline phosphatase (ALP) catalytic chemistry would then trigger the transition of the interparticle interplay from the CdS QDs-Au NPs to the CdS QDs-Ag NPs systems for the microRNA detection due to the dependence of the photocurrent quenching on the target concentration. This work not only provided a unique method for EPI generation among the PEC nanosystems but also offered a versatile and general protocol for future PEC bioanalysis development.

In this work, we present a novel energy-transfer (ET)-based photoelectrochemical (PEC) probing of DNA–protein interactions, which associates intimately with many important intracellular processes in transcriptional regulatory networks. Specifically, Au nanoparticles (NPs) were confined onto the CdS quantum dots (QDs) functionalized PEC surface by the formation of duplex DNA, the subsequent binding of the TATA binding protein (TBP) and the resulting distortion of the Au NPs capped DNA sequence could adjust the interparticle distance and thereby modulate the PEC performance of CdS QDs through the ET process between the CdS QDs and Au NPs. Using the duplex DNA sequence as a rigid spacer, the relationship between the photocurrent quenching effect and the spacing distance was also studied and some experimental conditions were optimized, on the basis of which a novel ET-based PEC TBP biosensor was realized with high sensitivity and selectivity.

In this Letter, on the basis of the CdS quantum dots functionalized TiO2 nanotubes electrode, we proposed a simultaneous photoelectrochemical (PEC) immunoassay of dual cardiac markers using specific enzyme tags of alkaline phosphatase (ALP) and acetylcholine esterase (AChE). ALP and AChE were integrated into the PEC system through the sandwich immunobinding and could specifically catalyze the hydrolysis of ascorbic acid 2-phosphate (AAP) or the acetylthiocholine (ATC) to in situ generate ascorbic acid (AA) or thiocholine (TC) for sacrificial electron donating. These two enzymes were thus used to differentiate the signals of two cardiac targets in connection with the sandwich immunorecognition and PEC responses to the corresponding electron donors. This strategy demonstrates a proof of principle for the successful integration of dual enzyme tags with PEC immunoassay that can potentially provide a general format for multiplexed PEC bioanalysis.

Antimicrobial susceptibility tests (ASTs) are important for confirming susceptibility to empirical antibiotics and detecting resistance in bacterial isolates. Currently, most ASTs performed in clinical microbiology laboratories are based on bacterial culturing, which take days to complete for slowly growing microorganisms. A faster AST will reduce morbidity and mortality rates and help healthcare providers administer narrow spectrum antibiotics at the earliest possible treatment stage. We report the development of a nonculture-based AST using a plasmonic imaging and tracking (PIT) technology. We track the motion of individual bacterial cells tethered to a surface with nanometer (nm) precision and correlate the phenotypic motion with bacterial metabolism and antibiotic action. We show that antibiotic action significantly slows down bacterial motion, which can be quantified for development of a rapid phenotypic-based AST.Keywords: bacterial metabolism; bacterial nanomotion; culture-free antimicrobial susceptibility tests; plasmonic imaging and tracking; real-time antimicrobial susceptibility tests; surface plasmon resonance microscopy;

Fingerprints are a unique characteristic of an individual. Recently, it has been realized that fingerprints carry more information about individuals than just their identity, for example, they may identify potential addicts and terrorists carrying explosives. Therefore, the development of imaging moieties capable of both fingerprint staining and drug/explosive visualization is of significant importance for forensic chemistry. Here we developed a nanohybrid comprising green- and red-emitting QDs for simultaneous fingerprint imaging and TNT visualization in fingerprints. The red-emitting Cu-doped ZnCdS (Cu–ZnCdS) QDs were embedded into silica nanoparticles and the green-emitting ZnCdS QDs were anchored onto the surface of the silica nanoparticles and further functionalized with polyallylamine (PAA). Both components of the nanohybrid, i.e., the PAA-functionalized green QDs and red QD-doped silica nanoparticles, could be explored for fingerprint imaging. Due to the formation of a Meisenheimer complex between TNT and PAA, the green-emitting QDs could be quenched by TNT, meanwhile the red-emitting QDs were inert. Therefore, the nanohybrid exhibited a traffic light-type fluorescence color change (green-yellow-red) to TNT concentration in the range of 40–400 μM. This method is promising for potential applications in security-screening needs in public areas such as airports and train stations.

Based on the assay of DNA binding proteins upon visible light irradiation, a photoelectrochemical sensor was constructed for successfully probing a DNA–protein interaction for the first time.

Using the DNA bio-gate and duplex-specific nuclease assisted target recycling, a facile electrochemiluminescence assay was developed for the sensitive detection of survivin mRNA.

A dual target-recycling amplification strategy for sensitive detection of microRNAs based on duplex-specific nuclease and catalytic hairpin assembly was reported for the first time.

Semiconductor nanocrystals usually suffer from weak electrogenerated chemiluminescence (ECL) emissions compared with conventional organic emitters. In this work, we propose, for the first time, a very convenient but effective way to greatly enhance ECL emission of semiconductor TiO2 nanotubes (NTs) by H2O2 and K2S2O8 as dual coreactants, generating ECL emission ca. 6.3 and 107 times stronger than that of K2S2O8 or H2O2 as an individual coreactant, respectively. Scanning electron microscopy, X-ray diffraction, and electron paramagnetic resonance spectral studies were carried out to investigate the ECL enhancement mechanism. The ECL enhancement of TiO2 NTs by the K2S2O8–H2O2 system was supposed to originate from the coordination of H2O2 to the TiO2 surface and the synergy effect between H2O2 and K2S2O8 in the ECL process. The coordination of H2O2 to the surface of TiO2 could stabilize the electrogenerated coreactant-related radical OH• (hydroxyl radical), which could obviously promote the amount of sulfate radical anion (SO4•—) near the electrode surface by inducing decomposition of K2S2O8 into SO4•— or inhibiting the consumption of SO4•— by its reaction with H2O. The holes (h+) released from SO4•— were injected into the valence band of TiO2, resulting in more TiO2+, which combined with the electrons coming from the conduction band with an enhanced light emission. Moreover, this enhancement effect was also applicable to ECL of a CdS nanocrystal film on a glass carbon electrode, with ca. 2.74- and 148.3-fold enhanced ECL intensity correspondingly, indicating wide applications in the development of semiconductor nanocrystal-based ECL biosensors.

Photoelectrochemical (PEC) immunoassay is an attractive methodology as it allows for an elegant and sensitive protein assay. However, advanced PEC immunoassay remains challenging and the established amplifications rely almost exclusively on the labeling of various enzymes, which usually suffer the inferior stabilities. Here we report the development and validation of the DNA labeling that leads to a unique amplification probe for the sensitive PEC immunoassay of HIV-1 capsid protein, p24 antigen, an important biomarker of human immune deficiency virus (HIV). Following the sandwich immunobinding, the DNA tags could be released and the subsequent dipurinization of the oligonucleotide strands enables the easy oxidation of free nucleobases at a CdTe quantum dots (QDs) modified ITO transducer. Such DNA tags induced PEC amplification and readout permits the exquisite assay of HIV-1 p24 antigen with high sensitivity. As compared to the existing method of enzymatic labeling, the easy preparation and stability of these labels make them very suitable for PEC amplification. Another merit of this method is that it separates the immunobinding from the PEC transducer, which eliminates the commonly existing affection during the biorecognition processes. This work paves a new route for the PEC immunoassay of HIV-1 p24 antigen and provides a general format for the PEC biomolecular detection by means of the DNA labeling.

•Photoelectrochemical sensor for Hg2 + was firstly fabricated by energy transfer.•Photocurrent was decreased by energy transfer between CdS QDs and Au NPs.•Interference can be neglected for the specific interaction of T–Hg2 +–T.•A simple and general protocol for PEC detection of metal ions was opened.A novel photoelectrochemical (PEC) sensor for mercury ions (Hg2 +) was fabricated based on the energy transfer (ET) between CdS quantum dots (QDs) and Au nanoparticles (NPs) with the formation of T–Hg2 +–T pairs. In the presence of Hg2 + ions, a T-rich single-strand (ss) DNA labeled with Au NPs could hybridize with another T-rich ssDNA anchored on the CdS QDs modified electrode, through T–Hg2 +–T interactions, rendering the Au NPs in close proximity with the CdS QDs and hence the photocurrent decrease due to the ET between the CdS QDs and the Au NPs. Under the optimal condition, the photocurrent decrease was proportional to the Hg2 + concentration, ranging from 3.0 × 10− 9 to 1.0 × 10− 7 M, with the detection limit of 6.0 × 10− 10 M.

•Double signal amplification with Au NPs and isothermal circular reaction is used.•Magnetic beads and aptamers are employed to capture and separate HL-60 cells.•Aptamer–target binding event is transformed into physically detectable signal.•The detection limit of this method could be equivalent down to 10 cells.Here we have developed a sensitive cancer cell amplified detection method which combined Au NPs enhanced electrochemiluminescence (ECL) of CdS nanocrystals (NCs) film, with isothermal circular amplification reaction of polymerase. In DNA circular amplification detection system, hairpin DNA beacon/Au NPs composite modified CdS NCs film was used as an ECL emitter. Messenger DNA is hybridized with the aptamer modified on magnetic beads (MBs) to form MB–Au bioconjugates. In the presence of HL-60 cell, the aptamer would conjugate with the glycoprotein at cell surface and messenger DNA sequence would be released. The released messenger DNA sequence was then introduced into the cycle amplification system to trigger circular polymerizations. This assay allows us to determine the released messenger DNA equivalent to 10 cells and exhibits a significant specificity for HL-60 cells.An ultrasensitive ECL cell sensor has been developed by combining Au NPs enhanced electrochemiluminescence (ECL) of CdS nanocrystals (NCs) film, with isothermal circular amplification reaction of polymerase. This sensor has the excellent selectivity, dramatic enhancement of ECL and lower detection limit for cancer cells detection.

•Applied high resolution SPR (SPR microscopy) to determine binding interactions of a protein with a single bacterial cell.•Achieved a detection limit of a single microbial cell; orders of magnitude higher compared to conventional SPR approaches.•New tool quantifies cell-to-cell variations in kinetics constants (e.g. KD).•Discovered large inherent heterogeneity in a microbial population.•Label-free, real-time, quantitative, high-resolution optical biosensor.Quantifying the interactions of bacteria with external ligands is fundamental to the understanding of pathogenesis, antibiotic resistance, immune evasion, and mechanism of antimicrobial action. Due to inherent cell-to-cell heterogeneity in a microbial population, each bacterium interacts differently with its environment. This large variability is washed out in bulk assays, and there is a need of techniques that can quantify interactions of bacteria with ligands at the single bacterium level. In this work, we present a label-free and real-time plasmonic imaging technique to measure the binding kinetics of ligand interactions with single bacteria, and perform statistical analysis of the heterogeneity. Using the technique, we have studied interactions of antibodies with single Escherichia coli O157:H7 cells and demonstrated a capability of determining the binding kinetic constants of single live bacteria with ligands, and quantify heterogeneity in a microbial population.

With the rapidly increasing demands for ultrasensitive biodetection, the design and applications of functional nanoprobes have attracted substantial interest for biosensing with optical, electrochemical, and various other means. In particular, given the comparable sizes of nanomaterials and biomolecules, there exists plenty of opportunities to develop functional nanoprobes with biomolecules for highly sensitive and selective biosensing. Over the past decade, numerous nanoprobes have been developed for ultrasensitive bioaffinity sensing of proteins and nucleic acids in both laboratory and clinical applications. In this review, we provide an update on the recent advances in this direction, particularly in the past two years, which reflects new progress since the publication of our last review on the same topic in Chem. Soc. Rev. The types of probes under discussion include: (i) nanoamplifier probes: one nanomaterial loaded with multiple biomolecules; (ii) quantum dots probes: fluorescent nanomaterials with high brightness; (iii) superquenching nanoprobes: fluorescent background suppression; (iv) nanoscale Raman probes: nanoscale surface-enhanced Raman resonance scattering; (v) nanoFETs: nanomaterial-based electrical detection; and (vi) nanoscale enhancers: nanomaterial-induced metal deposition.

A ratiometric electrochemiluminescent biosensor for the detection of microRNAs based on cyclic enzyme amplification and distance dependent resonance energy transfer was reported for the first time.

In this work, we report a simple and novel electrochemical multiplexed immunosensor on a flexible polydimethylsiloxane (PDMS) slice deposited with 8 × 8 nano-Au film electrodes for simultaneous detection of prostate specific antigen (PSA), prostate specific membrane antigen (PSMA), and interleukin-6 (IL-6). Primary antibodies linked with magnetic beads (Ab1-MBs) were modified on the nano-Au film electrodes via magnetic force. In the presence of corresponding antigen, horse radish peroxidase–secondary antibody-conjugated gold nanorods (HRP-Ab2-gold NRs) were brought into the surface of electrodes, generating obvious electrochemical signals of H2O2 reduction reactions. Based on this, the designed immunosensor provide good performance in sensitivity and specificity during the detection of above three biomarkers for prostate cancer. The electrochemical multiplexed immunosensor was verified for selective and accurate detection of complex samples in human serum. Data suggested that the reported multiplexed immunosensing strategy holds great promise for applications in clinical assay and diseases diagnosis.Keywords: electrochemical immunosensor; flexible electrode; microchip array; multiplexed measurement; prostate cancer

We present a facilely prepared graphene oxide (GO)/ poly(dimethylsiloxane) (PDMS) composite by dispersing nanosized GO in PDMS. On the basis of the combination of photothermal effects of GO and grafted thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), an optical-driving approach for remote control of localized wettability is realized. And this method has been successfully applied in the spatially controlled reversible protein adsorption in microfluidic devices.Keywords: protein adsorption, microfluidics, graphene, photothermal conversion; wettability

An ideal nanoporous poly(N-isopropylacrylamide) membrane has been fabricated in glass microchannels by means of spatially controlled photopatterning technology for a high level of enrichment and cleanup of nucleic acids.

Using CdS QD-tagged mercury-specific oligonucleotides, a novel folding-based photoelectrochemical sensor has been successfully fabricated for reagentless and highly sensitive Hg2+ detection.

Photoelectrochemical (PEC) immunoassay has received increasing attention owing to its good analytical performance and attractive potential for future protein assay. This Letter represents a novel and general strategy for elegant PEC immunoassay of the important cardiac marker troponin T (cTnT) at neutral conditions. Specifically, we first developed an efficient CdS quantum dots (QDs)/TiO2 nanoparticles (NPs) photoelectrode, on the basis of which an exquisite β-galactosidase (β-Gal) catalytic system was integrated with sandwich immunobinding for probing cTnT. In pH 7.4, β-Gal could catalyze the conversion of p-aminophenyl galactopyranoside (PAPG) to p-aminophenol (PAP), which could be easily photo-oxidized to p-quinone imine (PQI). Because the resulting photocurrent was directly related with the target concentration, an innovative PEC immunoassay could be realized for cTnT detection. The neutral operating condition of this protocol would greatly contribute to its wide applicability for protein assay. This work provides the first PEC immunoassay toward cardiac marker and, more significantly, opens a different perspective for future PEC immunoassay development through a general sensing protocol.

Surface plasmon resonance (SPR) has become an indispensable tool for label-free detection and quantification of molecular binding. Traditionally, the principle of SPR biosensors is described with a stratified medium model, in which discrete molecules are approximated with a uniform thin film. With the recent technical advances, SPR can now detect extremely low coverage of molecules, which raises the question of the validity of the traditional model. Here, we present combined theoretical, numerical and experimental analysis of SPR detection principle by considering the discrete nature of the molecules (particles). Our results show that the stratified medium model can provide reasonable description of SPR biosensors for relatively high coverage and weakly scattering samples. However, interference between the SPR images of individual particles needs to be considered for high spatial resolution images and for strong scattering samples at certain incident angles of light.

•Photoelectrochemical (PEC) bioanalysis•Mini review•Introductory concepts and main principles are provided.•The basic signaling mechanisms are highlighted using recent illustrative examples.Photoelectrochemical (PEC) bioanalysis has attracted considerable research interest due to its desirable properties, and its rapid evolution has resulted in great progress in bioanalytical applications. This mini review aims to provide a snapshot of the introductory concepts and main principles of PEC bioanalysis, as well as the basic classification of the established signaling strategies with recent illustrative examples.

•A microarray with 8 × 5 pairs of ITO and 8 Pt-Ag/AgCl coaxial electrodes was built.•Each cell with 2 ITO discs could be constructed by patterning PDMS upon ITO glass.•Pt-Ag/AgCl coaxial electrode with compact structure was removeable and durable.•Detecting units on the chip were mutually independent and owned well uniformity.•Two tumor markers were detected simultaneously with high-throughput manner.Here a novel electrochemical microarray platform towards high-throughput detection is presented. This microarray owns 8 × 5 well-organized oval cells and 8 × 5 pairs of ITO discs (two ITO discs for each pair in one cell). 8 mobile and aligned Pt–Ag/AgCl coaxial electrodes with compact configuration, where Pt column is used for counter electrode and Ag/AgCl for reference electrode, are inserted in 8 cells separately and made up 8 groups of three-electrode detection system together with 8 pairs of ITO discs. To demonstrate the applicability of such design, two kinds of bioconjugates, carboxyl graphene nanosheets–methylene blue (CGS–MB) and carboxyl graphene nanosheets–Prussian blue (CGS–PB) nanocomposites selected as model redox indicators and crosslinked with two kinds of antibodies were coated on the pair of ITO discs to realize a high-throughput detection of two tumor markers based on the increasing spatial blocking and impedance from the formed immunocomplex.

•An ITO bipolar array was designed.•AgNP-rGO composites were simultaneously coated on all cathodes of a bipolar array by one-step electrodeposition.•AgNP-rGO composites exhibited notable electrocatalytic activity to H2O2.•This bipolar array realized high-throughput visual detection of H2O2 by ECL imaging.An ITO bipolar array for electrochemiluminescence (ECL) imaging of H2O2 was reported. Silver nanoparticle-reduced graphene oxide (AgNP-rGO) composites were simultaneously coated on the cathodes of a bipolar array via a one-step electrodeposition approach. Compared to naked ITO, the above composites exhibited notable electrocatalytic activity to H2O2. The concentration of H2O2 could be indicated by the ECL image of Ru(bpy)32 +/2-(dibutylamino) ethanol (DBAE) at anodes based on charge balance. This chip system, not only provides a fast manner to prepare nanocomposites on bipolar electrodes (BPEs), but also can realize high-throughput visual detection.

The capability of imaging and detecting single DNA molecules is critical in the study, analysis, and applications of DNA. Fluorescence imaging is a widely used method, but it suffers from blinking and photobleaching, and fluorescence tags may block or affect binding sites on DNA. We report on label-free imaging of single DNA molecules with a differential plasmonic imaging technique. The technique produces high contrast images due to the scattering of surface plasmonic waves by the molecules and the removal of background noises and interference patterns, allowing for quantitative analysis of individual DNA molecules. Simulation of the images based on a scattering model shows good agreement with the experiment. We further demonstrate optical mapping of single DNA molecules.Keywords: label-free imaging; optical mapping; single molecule analysis; surface plasmon resonance microscopy; λ-DNA

A reusable potassium ion biosensor was reported for the first time based on the reversible DNA structural change and the interaction between surface plasmons of Au nanoparticles (NPs) and the ECL emission of CdS nanocrystals (NCs).

A new dual-functional electrochemical biosensor for the detection of prostate specific antigen (PSA) and telomerase activity was successfully developed based on a sandwich immunobinding format and telomerization assisted hemin–G-quadruplex-based DNAzyme as a biolabel.

In this work a novel microfluidic platform for cell culture and assay is developed. On the chip a static cell culture region is coupled with dynamic fluidic nutrition supply structures. The cell culture unit has a sandwich structure with liquid channels on the top, the cell culture reservoir in the middle and gas channels on the bottom. Samples can be easily loaded into the reservoir and exchange constantly with the external liquid environment by diffusion. Since the flow direction is perpendicular to the liquid channel on the top of the reservoir, the cells in the reservoir are shielded from shear-force. By assembling the basic units into an array, a steady concentration gradient can be generated. Cell culture models both for continuous perfusion and one-off perfusion were established on the chip. Both adherent and suspended cells were successfully cultured on the chip in 2D and 3D culture modes. After culturing, the trapped cells were recovered for use in a later assay. As a competitive candidate for a standard cell culture and assay platform, this chip is also adaptable for cytotoxicity and cell growth assays.

To date, almost all the established photoelectrochemical (PEC) enzymatic biosensors require the surface-confinement procedure to immobilize enzyme as biorecogniton element for probing various analytes of interest. This Letter develops a novel example without such necessity. Specifically, we first prepared a BiOI nanoflakes (NFs)/TiO2 nanoparticles (NPs) p–n heterojunction as the photoelectrode, on the basis of which acetylcholine esterase (AChE) antibody was introduced via the bridging of protein A. In such a system, enzyme could keep its optimal state in the solution if in the absence of inhibitor; otherwise, the degree of enzyme inhibition would correlate closely with the concentration of inhibitor. After immunoreaction between AChE and its antibody, the inhibitor concentration could then be determined by the biocatalytic reaction-controlled PEC response. Integrated with other enzyme-based biosystems, this simple configuration could serve as a general method for assaying enzyme inhibition or activities.

This paper describes a portable thermo-powered high-throughput visual electrochemiluminescence (ECL) sensor for the first time. This sensor is composed of a tiny power supply device based on thermal-electrical conversion and a facile prepared array electrode. The ECL detection could be conducted with thermo-power, which is easily accessible. For example, hot water, a bonfire, or a lighted candle enables the detection to be conducted. And the assay can be directly monitored by the naked eye semiquantitatively or smart phones quantitatively. Combined with transparent electrode and array microreactors, a portable high-throughput sensor was achieved. The portable device, avoiding the use of an electrochemical workstation to generate potential and a photomultiplier tube to receive the signal, is not only a valuable addition for traditional methods but also a suitable device for field operation or point-of-care testing.

Usually, the photoelectrochemical (PEC) bioanalysis necessitates ready photoactive materials as signal sources to convert the specific biological events into electrical signals. Herein, the first PEC bioanalysis without the necessity of ready visible-light-active species was demonstrated. We use an enzyme catalytic process to couple with the unique surface chemistry of semiconductive nanocrystalline, whereby its electronic properties could be modified spontaneously during the enzymatic reaction. Specifically, the enzymatic hydrolysis of ascorbic acid 2-phosphate by alkaline phosphatase is allowed to interact on the TiO2 nanoparticles (NPs) matrix. PEC tests reveal that the self-coordination of the biocatalyzed enediol-ligands onto the undercoordinated surface defect sites would in situ form a ligand-to-metal charge transfer (CT) complex, endowing the inert semiconductor with strong absorption bands in the visible region, and hence underlying a novel and general PEC bioanalysis strategy.

•Employing PSA and survivin mRNA as dual-biomarkers in prostate cancer detection.•Nano-structured gold electrode and direct electrochemical output.•Logic gate of “AND” mode greatly reduced the possibility of false-positive assay.As single biomarker often has inadequate predictive value in clinical examination, we designed a dual-biomarker “AND” logic device that defines the concentration of prostate-specific antigen (PSA) and survivin mRNA as inputs and the increase in faradaic current from intercalation agent Co(phen)33 + as output for prostate cancer (CaP) diagnosis on Au nano-film covered gold electrode surfaces. Primary capture antibody (Ab1) was first immobilized on AuNP electrode, then while both PSA and survivin mRNA exist, current of Co(phen)33 + observably increased due to the formation of dsDNA structure between survivin antisensoligonucleotide connected secondary detection antibody (Ab2) and survivin mRNA. And when one of the two biomarkers was absent, no obvious current increment was found. Thus the designed “AND” logic gate greatly reduced the possibility of false-positive assay from non-cancerous prostate diseases such as prostatic hyperplasia and prostatitis in diagnosis of CaPs.

•Photoelectrochemical (PEC) Pb2 + sensing was achieved firstly.•G-quadruplex-based DNAzyme and biocatalytic precipitation were coupled.•Amplified ultrasensitive PEC detection of Pb2 + was realized.•It opened a different horizon for PEC ions sensing.A sensitive photoelectrochemical (PEC) approach for Pb2 + sensing was achieved firstly with the coupling of G-quadruplex-based DNAzyme and biocatalytic precipitation (BCP) on a CdS quantum dots electrode. Pb2 + can induce the conformational change of K+-stabilized G-quadruplex-based DNAzyme, leading to the decrease of the catalytic activity to H2O2-mediated 4-chloro-1-naphthol oxidation (BCP reaction). From the respective BCP reaction that monitors the event of DNAzyme deactivation, a novel PEC Pb2 + sensor could be realized with a detection limit of 1.0 × 10− 8 M.

A new photoelectrochemical immunoassay for prostate-specific antigen (PSA) was successfully developed with high sensitivity via immunogold labeling.

Based on the amplified signal from SiO2@CdS nanocomposites integrated with K-doped graphene, a new electrochemiluminescence biosensor was developed for the successful detection of transcription factor TATA-binding protein (TBP).

Continuous CaCO3 hollow nanoparticle generation at room temperature with simultaneous molecule doping is realized on a liquid–gas dual phase microfluidic system.

In the present work we design a novel aptamer-based silver nanosensor for one-spot simultaneously detection of multiple proteins. SS-DNA modified AgNPs were immobilized on the aldehyde coated glass slide to form an AgNP array. Then dye-labeled aptamer sequences were allowed to hybridize with their complementary strands assembled on the surface of AgNPs. The target proteins were introduced to associate with the corresponding aptamers to form the aptamer–target complexes. The removal of the aptamer–target complexes resulted in a remarkable decrease in fluorescent signals. This nanosensor is found to be highly sensitive for the detection of proteins. When thrombin was employed as a sample model, the limit of detection of the optimized nanosenor was 0.4 fmol with a linear response of 0.8 fmol to 0.5 pmol. We further demonstrated the multiple protein detection of IgE and thrombin using multicolor silver nanoprobes, which shows effective recognition of the relative protein individually or simultaneously. This silver nanosensor offers a unique heterogeneous approach for protein detection with several advantages, such as high sensitivity, rapidity, high throughput, and miniaturization.

In the present study, we report a novel aptasensor based on silver nanoparticle enhanced fluorescence for the detection of adenosine. First, the distance dependence nature of silver nanoparticle enhanced fluorescence was investigated through fluorescent dyes modified oligonucleotides to control the spacing distance between dyes and AgNP. The results showed that the fluorescence intensity reached the maximum value with the spacing distance of dyes about 8 nm from AgNP surface. The fluorescence intensity decreases when the spacing distance is either above or below this value. Based on this result, a fluorescence switch is constructed. In the “OFF” state, without the target molecules, there is a greater spacing distance between the Cy3 dyes and the AgNP giving comparatively lower fluorescence intensity. While in the “ON” state, in the presence of target molecules, the fluorescence signals increased for the conformation structure change of the aptamer which shorten the spacing distance between the Cy3 dyes and the AgNP to 8 nm. Using adenosine as target, the aptasensor produced a linear range from 200 nM to 200 μM with a correlation coefficient of 0.9949 and the detection limit was 48 nM estimated using 3σ. The aptasensor was also found to be specific in targeting adenosine. The presented method shows a new strategy of combining aptamer recognition and silver nanoparticle for fluorescence signal enhancement and increasing sensitivity.Highlights► Aptasensor designed based on MEF effect of AgNPs. ► Distance dependence nature of MEF investigated by Cy3 modified oligonucleotides. ► Conformation change of aptamers changes the fluorescence of Cy3 on the AgNPs. ► A fluorescence switch constructed for detection of adenosine.

In this work a novel microdevice sensor has been developed by plating gold on the PDMS surface to generate a sandwich-type gap electrode for DNA detection. The microdevice utilizes a gold band electrode–PDMS–gold band electrode configuration and the minimum detectable volume could be as low as 5 μL. The 20 μm PDMS-based gap was chemically modified with DNA capture probes and DNA sandwich hybrids were formed with the addition of DNA target and silver nanoparticle probes. To increase detection sensitivity, parallel detection zones have been developed in which the relevant resistances decrease substantially upon hybridyzation. By measuring the change in electrical conductivity, the DNA target in the concentration range of 1000–0.1 nM can be assayed and the limit of lowest detectable concentration was achieved at 0.01 nM.

In this article, an electrochemically direct stripping approach based on silver nanoparticles (AgNPs) labeled with antibody was proposed. To prepare AgNPs labels, glutathione (GSH) was chemically absorbed on the surface of AgNPs through its free thiol groups. Glutaraldehyde was used as a coupling reagent, its two aldehyde groups reacted with the amino group of GSH absorbed on the AgNPs surfaces and the amino groups of antibodies, respectively. The resulting labeled electrochemical active nanoparticles could recognize the proteins specifically via the immobilized antibody. To prove the electrochemical property of labeled AgNPs, human IgG was used as a model protein sample to be immobilized on a screen printed electrode (SPE) and the goat-anti-human IgG labeled AgNPs was added onto the surface of the SPE, followed by differential pulse voltammetric (DPV) method. With the oxidation of AgNPs labels coupled on the electrodes, the concentration of hIgG could be assayed directly and calculated. The dynamic concentration was in the range of 1–1000 ng/mL and the detection limit was 0.4 ng/mL (S/N = 3). In addition, the presented method was also compared to indirect electrochemical stripping detection by dissolving AgNPs labels with nitric acids and the results showed advantages such as lower detection limit, rapidity and simplicity.Research highlights► In this article an electrochemically direct stripping approach based on silver nanoparticles (AgNPs) labeled with antibody was proposed. ► Human IgG was used as a model protein sample to be immobilized on a screen printed electrode and the goat-anti-human IgG labeled AgNPs was added onto the surface of the SPE. ► With the oxidation of AgNPs labels, the concentration of hIgG could be assayed directly and calculated. ► The dynamic concentration was in the range of 1–1000 ng/mL and the detection limit was 0.4 ng/mL (S/N = 3).

A versatile DNA recognition system using cadmium sulfide nanoparticles (CdS NPs) as labels was proposed for ultrasensitive detection of specific sequence DNA based on target recycling. This strategy utilized the magnetic particles (MNPs) for the immobilization of linker DNA and CdS NPs and the subsequent target DNA hybridization. Using the unique characteristic of nicking endonuclease for cutting one specific strand of double strand DNA (ds DNA), the linker DNA could be transected and the target DNA could be liberated for re-hybridization and hence the amount of released CdS NPs was enhanced. Due to the advantage of the MNPs and signal amplification from the target recycling, the analyte DNA could be detected by the square-wave stripping voltammetry (SWV) in a wide linear range from 0.4 fM to 100 fM with the detection limit down to 0.08 fM. The proposed DNA detection strategy possesses high sensitivity, satisfactory reproducibility and excellent stability, which might have potential in other DNA biological assays.

There has been great interest in developing new nucleic acid and protein detection methods for both clinical and numerous non-clinical applications. In a long-lasting effort to improve the detection ability of bioassays, functional nanomaterials have been actively explored to greatly enhance the sensitivity during the last two decades. This tutorial review focuses on recent progress in biosensor development by exploiting several unique optical, electronic and catalytic properties of a range of nanomaterials, such as gold nanoparticles, quantum dots, silicon nanowires, carbon nanotubes and graphene. In addition, a perspective on new opportunities offered by emerging technologies (e.g. DNA nanotechnology) is provided.

In this paper, we present a simple method to fabricate gold film patterns and PDMS patterns by air plasma assisting microcontact deprinting and printing transfer approaches. Chemical gold plating is employed instead of conventional metal evaporation or sputtering to obtain perfect gold film both on flat and topographic PDMS chips, and complicated SAM precoating is replaced by simple air plasma treatment to activate both the surface of gold film and PDMS. In this way, large area patterns of conductive gold film and PDMS patterns could be easily obtained on the elastomeric PDMS substrate. Both the chemical plating gold film and transferred gold film were of good electrochemical properties and similar hydrophilicity with smooth and conductive surface, which made it potentially useful in microfluidic devices and electronics. The gold transfer mechanism is discussed in detail. For typical applications, a cell patterning chip based on the gold pattern was developed to imply the interfacial property, and dielectrophoresis control of live cells was carried out with the patterned gold as interdigital electrodes to show the conductivity.Keywords: cell; dielectrophoresis; gold film; microcontact deprinting; pattern; transfer printing

Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H2O2. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H2O2. The resulting ECL biosensors showed a linear response to the concentration of H2O2 ranging from 1.0 × 10−8 to 6.6 × 10−4 mol L−1 with a detection limit of 5 nmol L−1 (S/N = 3) and good stability and reproducibility.

Boronate affinity solid phase microextraction (BA-SPME) is a new format appeared recently with great potential for specific extraction of cis-diol-containing compounds. Unlike conventional SPME, BA-SPME relies on covalent interactions and thereby features with specific selectivity, eliminated matrix effect and manipulable capture/release. However, only on-fiber BA-SPME and its off-line combination with high performance liquid chromatography (HPLC) have been reported so far. In this study, we report on-line coupling of in-tube BA-SPME with HPLC–electrospray ionization tandem mass spectroscopy (in-tube BA-SPME-HPLC–ESI-MS/MS) for the specific and sensitive determination of cis-diol-containing biomolecules. A boronate affinity extraction phase was prepared onto the inner surface of the capillary by copolymerization of vinylphenylboronic acid (VPBA) and ethylene glycol dimethacrylate (EDMA). The extraction conditions were optimized by choosing appropriate extraction/desorption solutions and extraction time. The extraction capacity, linear range, reproducibility and life-time were investigated. The developed method was successfully applied for the determination of dopamine in urine samples. Since many cis-diol-containing compounds are of great biological importance, the in-tube BA-SPME-HPLC method can be a promising tool.

A core-shell Rhodamine B-doped SiO2 nanoparticle was synthesized and its fluorescent intensity was found to be 1000 times higher than that of individual Rhodamine B molecule. The doped nanoparticles were further conjugated with streptavidin and the resulting nanoparticles were used in the detection of reverse-phase protein microarrays, in which human IgG of various concentrations was first immobilized on aldehyde-modified glass slides and then biotinlyated goat anti human IgG as well as the labeled nanoparticles were sequentially conjugated. The calibration curve is linear over the range from 800 fg to 500 pg and the limit of detection is 100 fg, which is 8 times lower than that of streptavidin-labeled Cy3 fluorescent dyes. The dye-doped SiO2 nanoparticles show potentials for the protein array detection.

Herein, a functional template made up of in situ synthesized silver nanoparticles (AgNPs) is prepared on polydimethylsiloxane (PDMS) for the spatial control of cell capture, where the residual Si−H groups in the PDMS matrix are used as reductants to reduce AgNO3 for forming AgNPs. In virtue of microfluidic system, a one-dimensional array pattern of AgNPs is obtained easily. Further combining with plasma treatment, a two-dimensional array pattern of AgNPs could be achieved. The obtained PDMS−AgNPs composite is characterized in detail. The PDMS−AgNPs composite shows good antibacterial property in E. coli adhesion tests. The patterns possess hifi and high resolution (ca. 8 μm). Cell patterns with high efficiency and spatial selectivity are further formed with the aid of H−Arg−Gly−Asp−Cys−OH (RGDC) tetrapeptide which is grafted on the AgNPs template. Cells immobilized on the template show a good ability for adhesion, spreading, migration, and growth.

In the present work, dual-functional DNA tweezers were constructed for the multiplex detection of thrombin and adenosine triphosphate (ATP). The aptamers for thrombin and ATP were respectively immobilized on magnetic beads (MBs). Then they hybridized with complementary sequences at the ends of opening strands Cin and Din. In the presence of thrombin and ATP, Cin and Din were released as the results of competition. The tweezers contained two symmetrical components, and six DNA strands were hybridized to form the closed state. When the opening strands were introduced, the tweezers were driven to the open state, releasing two inert double-stranded waste products.

In the current paper, enzyme enhanced simultaneous quantitative determination of multiple DNA targets based on capillary electrophoresis (CE) was described. We used three biotin-modified DNA probes, which reacted with avidin-conjugated horseradish peroxidase (avidin-HRP) conjugate to obtain the HRP labeled probes, to hybridize with three corresponding targets. The resulting mixture containing double-strand DNA (dsDNA)-HRP, excess single-strand DNA (ssDNA)-HRP and remaining avidin-HRP was separated by capillary electrophoresis, and then the system of HRP catalyzing H2O2/o-aminophenol (OAP) reaction was adopted. The catalytic product was detected with electrochemical detection. With this protocol, the limits of quantification for the hybridization assay of 21-, 39- and 80-mer DNA fragments were of 1.2 × 10−11, 2.4 × 10−11 and 3.0 × 10−11 M, respectively. The multiplex assay also provided good specificity without any cross-reaction.

A new format of solid phase microextraction (SPME), boronate affinity SPME, was proposed for the first time for covalent extraction of cis-diol containing biomolecules. This new SPME format is based on the reversible complex formation between boronic acids and 1,2- and 1,3-cis-diols. The complex formation and dissociation can be facilely controlled by changing pH. An extracting phase of poly-3-aminophenylboronate (polyAPBA) electrochemically deposited on a metal wire was employed to demonstrate the concept of this new methodology. Catechol and riboflavin were used as the test analytes, and the SPME extraction was combined off-line with high-performance liquid chromatographic (HPLC) separation followed by UV absorbance or fluorescence detection. Fundamental aspects, such as selectivity, extraction/desorption equilibrium, linearity, effect of competing compounds, reproducibility and life-time, were first investigated. Then the developed method was applied to beer samples since the content of riboflavin plays an important role in the flavor stability of beverages. Excellent performance of the SPME fibers was observed for both standard and real samples. Particularly, the expected excellent features of the polyAPBA extracting phase were experimentally verified, which include specific selectivity, eliminated matrix effect and manipulable capture/release. The new methodology of SPME can be a promising tool since a lot of 1,2- and 1,3-cis-diol-containing compounds are of great biological importance.

We report a simple and novel method of stirring-only-driven accumulation and electrochemical determination of arsenite (As(III)) with both of the oxidation and reduction peaks associated with As(0)/As(III) using a gold nanofilm electrode in neutral solution. Under stirring, a large amount of As(III) was deposited on the modified electrode and the electrochemical response was greatly amplified. The accumulated As(III) on the electrode showed well-defined redox couple in 0.1 M blank phosphate buffer solution (pH 7.0), which could be used for the measurement of As(III). Under optimal conditions, As(III) could be detected in the range from 0.20 to 375 ppb with a detection limit of 0.04 ppb. In particular, with the use of the reduction peak of As(III) the modified electrode exhibits excellent performance for As(III) determination even in the presence of abundant Cu(II). The regeneration of the electrodes is facile with good reproducibility. The electrochemical system was applied to analyze As(III) in lake water, As(III) spiked tap water and drinking water.

In this paper, we present a novel approach for preparing patterned Au/poly(dimethylsiloxane) (PDMS) substrate. Chemical gold plating instead of conventional metal evaporation or sputtering was introduced to achieve a homogeneous gold layer on native PDMS for the first time, which possesses low-cost and simple operation. An electrochemical oxidation reaction accompanied by the coordination of gold and chloride anion was then exploited to etch gold across the region covered by electrolyte. On the basis of such an electrochemical etching, heterogeneous Au/PDMS substrate which has a gold “island” pattern or PDMS dots pattern was fabricated. Hydrogen bubbles which were generated in the etching process due to water electrolysis were used to produce a safe region under the Pt auxiliary electrode. The safe region would protect gold film from etching and lead to the formation of the gold “island” pattern. In virtue of a PDMS stencil with holes array, gold could be etched from the exposed region and take on the PDMS dots pattern which was selected to for protein and cell patterning. This patterned Au/PDMS substrate is very convenient to construct cytophobic and cytophilic regions. Self-assembled surface modification of (1-mercaptoundec-11-yl)hexa(ethylene glycol) on gold and adsorption of fibronectin on PDMS are suitable for effective protein and cell patterning. This patterned Au/PDMS substrate would be a potentially versatile platform for fabricating biosensing arrays.

We presented a simple approach for in-situ synthesis of poly(dimethylsiloxane) (PDMS)–gold nanoparticles composite film based on the special characteristics of PDMS itself. It is an environmentally safe synthesis method without the requirement of additional reducing/stabilizing agents. The region where the resulting gold nanoparticles distribute (in the matrix or on the surface of the polymer) and the size of the nanoparticles, as well as the colour of the free-standing films, can be simply controlled by adjusting the ratio of curing agent and the PDMS monomer. The chemical and optical properties of these composite films were studied. Using such a method, gold nanoparticle micropatterns on PDMS surfaces can be performed. And based on the gold nanoparticles micropattern, further modification with antibodies, antigens, enzymes and other biomolecules can be achieved. To verify this ability, an immobilized glucose oxidase (GOx) reactor in microchannels was built and its performance was studied. The experiments have shown that the resulting composite film may have a lot of potential merits in protein immobilization, immunoassays and other biochemical analysis on PDMS microchips.

A simple one-step biomimetic coprecipitation method is reported to prepare a protein based biosensor by immobilizing calcium phosphate/hemoglobin composite nanoparticles directly onto glassy carbon electrode surface. Atomic force microscopy (AFM), attenuated total reflection spectra (ATR) and electrochemical method were used to characterize the as-prepared composite nanoparticles. Hb in the composite film kept their biological activity well, realized its direct electrochemistry with the formal potential of −0.363 V in pH 7.0 phosphate buffer solution and gave excellent electrocatalytic performance to the reduction of hydrogen peroxide, by which the mediator-free biosensors could be fabricated. Compared to other immobilization methods, this system not only avoids the tedious synthesis of nanoparticles and the use of reagent detrimental to biomolecules but also possesses the advantages of simple preparation and low cost.

Single-walled carbon nanotubes (SWCNTs) selectively wrapped by a water-soluble, environmentally friendly, biocompatible polymer chitosan (CHI) were employed for the construction of a bioelectrochemical platform for the direct electron transfer (DET) of glucose oxidase (GOD) and biosensing purposes. Scanning electron microscopy and Raman spectroscopy were used to investigate the properties of the SWCNT–CHI film. The results show that the preferentially wrapped small-diameter SWCNTs are dispersed within the CHI film and exist on the surface of the electrode as small bundles. The DET between GOD and the electrode surface was observed with a formal potential of about ca. −460 mV vs. SCE in phosphate buffer solution. The heterogeneous electron transfer rate constant and the surface coverage of GOD are estimated to be 3.0 s−1 and 1.3 × 10−10 mol/cm2, respectively. The experimental results demonstrate that the immobilized GOD retains its catalytic activity towards the oxidation of glucose. Such a GOD/SWCNT–CHI film-based biosensor not only exhibits a rapid response time, a wide linear rang and a low detection limits at a detection potential of −400 mV but also shows the effective anti-interference capability. Significantly improved analytical capabilities of the GOD/SWCNT–CHI/GC electrode could be ascribed to the unique properties of the individual SWCNTs and to the biocompatibility of CHI.

Human immunoglobulin E (hIgE) is such an important protein, because of its involvement in allergic disease, that it is of significance to study the interactions between it and its recognizing elements. In this report an analytical strategy based on surface plasmon resonance (SPR) was developed to probe the pattern of interaction between hIgE and its recognizing molecules, including aptamers and antibodies. The affinity constants of hIgE for the antibody and the aptamer were compared first; the aptamer has more affinity than the antibody for human IgE. To study their pattern of interaction, three different binding approaches, including adding the antibody and the streptavidin-coupled aptamer to the sensing surface, were designed. The results showed that hIgE captured on the sensing surface could form a multivalent complex with the aptamer. An ELISA-like assay using the aptamer as both capture and detection probes was then developed. This work highlights an SPR method for characterizing the interaction between the protein and aptamers that is useful for study of biomolecular interaction patterns and binding properties.

A novel method for rapid separation and determination of ascorbic acid and uric acid has been developed with a polycation-modified poly(dimethylsiloxane) (PDMS) microchip under a negative-separation electric field. Just by flushing the microchip with aqueous solutions of the polycations, poly(allylamine) hydrochloride, poly(diallyldimethylammonium chloride) or chitosan could be stably coated on the PDMS microchannel surface, which resulted in a reversed electroosmotic flow and thus the rapid and efficient separation of the two substrates. Factors influencing the separation, including polycation category, buffer solution, detection potential and separation voltage, were investigated and optimized. The cheapness, rapid analysis speed and the successful analysis of human urine make this microsystem attractive for application in clinics.

The separation of three kinds of aminophenol isomers were achieved within 1 min in polyelectrolytes multilayers modified PDMS microchips by layer-by-layer assembly with electrochemical detection (EC). Two polyelectrolytes, poly(dially dimethyl ammonium chloride) (PDDA) and poly(sodium-4-styrene-sulfonate) (PSS) were used to form polyelectrolyte multilayers (PEMs). The surface characteristic of the modified microchip was studied by XPS. The electroosmotic flow (EOF) on PEMs modified PDMS microchips was more stable than that of the native PDMS microchips and the adsorption of samples was greatly reduced on PEMs modified PDMS microchips during the electrophoretic process. The column efficiencies on PEMs modified microchip were increased by 100 times and the signals enhanced by 2 times compared with those of native microchips. The separation conditions such as running buffer pH, running buffer concentration and separation voltage were also optimized.

A mixture of five amino acids including arginine, histidine, phenylalanine, serine and glutamic acid was successfully separated in microchip capillary electrophoresis and detected with laser-induced fluorescence (LIF) detector. These amino acids were labeled with 5-(4, 6-dichloro-s-triazin-2-ylamino) fluorescein (DTAF). The analyses were performed on two kinds of modified poly(dimethylsiloxane) (PDMS) microchips. One kind of chip was simply treated with oxygen plasma (OP-chip), and the other was further modified by coating double layers of non-ionic polymer poly(vinyl alcohol) (PVA) after plasma oxidization (PVA-chip). The derivatization condition of amino acids by DTAF was optimized. The properties of the two modified PDMS microchips were studied and separation conditions, such as the buffer pH, buffer concentration and separation voltage, were also optimized. The column efficiencies of the two microchips were in the range of 193,000–1,370,000 plates/m. The DTAF-labeled amino acids were sufficiently separated within 50 s and 90 s in 2.5 cm channels on OP-chip and PVA-chip, respectively.

CdS nanoparticles composited with carbon nanotubes not only enhances their electrochemiluminescent intensity but also decreases their ECL starting potential; such a property would promote the application of quantum dots in fabricating sensors for chemical and biochemical analysis.

A biocompatible, nanoporous ZnO film was prepared on graphite electrode by the simple electrodeposition method. Based on the film’s strong adsorption ability and friendly microenvironment, it can be used as a good matrix to immobilize myoglobin (Mb) through simple adsorption. Moreover, the entrapped Mb realized direct electron transfer with the electrode and displayed an elegant catalytic activity toward the reduction of hydrogen peroxide, nitrite, and trichloroacetic acid, by which the mediator-free biosensors could be fabricated. Atomic force microscopy, UV-Vis spectra, electrochemical impedance spectroscopy, and cyclic voltammetry, etc. were used to characterize the nanoporous ZnO film and Mb-modified ZnO film. Compared to other methods, electrodeposition of porous material supplied a more simple and convenient approach to prepare biocompatible materials for biosensors.

We report on the formation of colloidal biocomposites resulting from the electrostatic self-assembly of negatively charged lactate oxidase (LOD) and oppositely charged nanoscaled cobalt phthalocyanine (NanoCoPc) colloid under enzyme-friendly conditions. The biocomposites were further used to fabricate lactate biosensors due to their excellent film-forming ability and strong adsorbability on the surface of glassy carbon electrode. The electrochemical assays of such films revealed a large capacity of NanoCoPc for the retention of LOD. Here, NanoCoPc colloid was not only used as carriers for immobilization of LOD, but also displayed intrinsic electrocatalytic activity for the oxidation of H2O2, a product of enzymatic reaction. A chitosan film containing MnO2 nanoparticles was further electrodeposited as an external layer, which could effectively eliminate the interference from ascorbic acid. Under optimal conditions, the biosensor showed a wide linear response to lactate in the range of 0.020–4.0 mM, with high sensitivity (3.98 μA cm−2 mM−1), as well as good reproducibility and long-term stability. The biosensor has been used for the determination of lactate in real samples with an acceptable accuracy.

A simple and controllable electrodeposition method for the formation of a chitosan–carbon nanotube nanocomposite film on an electrode surface was proposed and further used for the construction of an electrochemical biosensor.

The single-crystalline Se nanotubes were synthesized on the surface of Au sheet electrode by cyclic voltammetry. In synthesis process, cetyltrimethyl ammonium bromide (CTAB) was used as soft-template. The formation mechanism of Se nanotubes was discussed. Furthermore, the deposits with other morphologies were also obtained by modulating parameters in the synthesis process. The products as-prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and laser Raman spectrograph (LRS). The electrochemical behavior of the Se nanotubes was studied by the linear scan voltammetry.

The Au particles have been intercalated within the gallery spaces of Zn–Al layered double hydroxides (LDHs). Synthesis of this material was obtained by ion-exchange of the LDH-nitrate precursor with AuCl4− anion followed by reduction with the sodium citrate. Elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), TEM and N2 sorption analyses have been used to characterize the material. TEM micrographs of LDH-Au revealed a typical porous material. Chemical analysis results showed that AuCl4− anions exchanged with nitrate anions. XPS analysis confirmed the deoxidization of the AuCl4− anions in the gallery after treatment with the sodium citrate. The XRD diffraction patterns of LDH-Au revealed that the layer structure is maintained after all synthetic steps. The XPS spectra, the elemental results and the TEM patterns proved the intercalation of Au particles into the gallery.

A novel solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles (NanoCoPc) as ionophore was fabricated without any need of auxiliary materials (such as membrane matrix, plasticizer, and other additives). The electrode was prepared by simple drop-coating NanoCoPc colloid on the surface of a glassy carbon electrode. A smooth, bright and blue thin film was strongly attached on the surface of the glassy carbon electrode. The electrode showed high selectivity for ascorbic acid, as compared with many common anions. The influences of the amount of NanoCoPc at the electrode surface and pH on the response characteristics of the electrode were investigated. To overcome the instability of the formal potential of the coated wire electrode, a novel electrochemical pretreatment method was proposed for the potentiometric sensor based on redox mechanism. This resulting sensor demonstrates potentiometric response over a wide linear range of ascorbic acid concentration (5.5 × 10−7 to 5.5 × 10−2 M) with a fast response (<15 s), lower detection limit (ca. 1.0 × 10−7 M), and a long-term stability. Furthermore, microsensors based on different conductors (carbon fiber and Cu wire) were also successfully fabricated for the determination of practical samples.

CdSe and PbSe nanowire arrays have been successfully prepared by a photochemical method in porous anodic aluminum oxide template from an aqueous solution of lead acetate, cadmium chloride and sodium selenosulfate in the presence of nitrilotriacetic acid. The products were characterized by XRD, TEM, SEM, PL and UV–vis.

This paper describes a solution-phase approach to the synthesis of selenium nanoparticles by reducing selenious acid solution with ascorbic acid in the presence of polysaccharides, such as chitosan (CTS), konjac glucomannan (KGM), acacia gum (ACG), and carboxymethyl cellulose (CMC) etc. The monodispersed spherical selenium colloid particles obtained were very stable in solution. The influences of temperature and ultrasonic on the morphology of selenium nanoparticles were also discussed.

It is essential for the information storage in DNA-based bio-chips to construct a reversible exchange interface of DNA. Here, a highly reproducible and reversible adsorption–desorption interface of DNA based on the nano-sized zirconia in different pH solution was successfully fabricated. The results showed that DNA can be adsorbed onto the nano-sized zirconia from its solution, and can desorb from the nanoparticles in 0.10 M KOH solution. When the matrix with nanoparticles returns to the DNA solution again, DNA can be re-adsorbed onto them as initial state. Moreover, the interaction of DNA with non-electroactive molecules, 2,2′-bipyridine, has been studied by electrochemistry method in the aid of probe Co(phen)33+. The experiments showed that when 2,2′-bipyridine was added into the test solution, the voltammetric peak currents of Co(phen)33+ decreased; and the decrease value of peak current against the concentration of 2,2′-bipyridine has a good Langmuir relationship, by which the equilibrium constant of interaction between 2,2′-bipyridine and DNA was estimated to be 1.57×104 M−1.

A novel integrated chemiluminescence (CL) flow sensor for the determination of adrenaline and isoprenaline is developed based on the enhancing effect of analytes on CL emission of luminol oxidized by periodate in alkaline solution. The analytical reagents luminol and periodate are immobilized on anion exchange resins, respectively, and packed in a glass tube to construct a reagentless sensor. The proposed sensor allows the determination of adrenaline and isoprenaline over the range from 2.0×10−8 to 1.0×10−5 g ml−1 and 2.0×10−7 to 5.0×10−5 g ml−1, respectively. The detection limits are 7.0×10−9 g ml−1 for adrenaline and 5.0×10−8 g ml−1 for isoprenaline with a relative standard deviation of 1.7% for the 1.0×10−7 g ml−1 adrenaline (n=11) and 2.1% for 1.0×10−6 g ml−1 isoprenaline (n=11). The sample throughput was 60 samples h−1. The sensor has been successfully applied to the determination of adrenaline and isoprenaline in pharmaceutical preparations.

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml−1 (3×10−8 mol l−1) and 4 ng ml−1 (3×10−8 mol l−1), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25–5 μg ml−1.

A reagentless chemiluminescence (CL) flow sensor is developed for the determination of hydrogen peroxide. The analytical reagent luminol was immobilized on anion-exchange resins and packed in a glass tube, the horseradish peroxidase (HRP) was immobilized on biocompatible chitosan (CHIT) membrane which was formed on the glass coil to construct a transparent sensing flow cell. The two segments are integrated to fabricate a reagentless flow biosensor. The properties of CHIT, HRP and CHIT–HRP films have been carefully characterized by Fourier transform infrared (FT-IR). The results indicate that HRP retains the essential feature of its native structure in the CHIT film. The sample throughput is 120 h−1 with small sample volumes (30 μl). The two linear working regions are 1.0×10−7 to 1.0×10−5 mol l−1 and 1.0×10−5 to 2.0×10−4 mol l−1. The detection limit is 4.0×10−8 mol l−1 (S/N=3) with a relative standard deviation of 1.1% for the 4.0×10−6 mol l−1 H2O2 solution in 31 repeated measurements. The sensor could be used for 3 months.

There has been great interest in developing new nucleic acid and protein detection methods for both clinical and numerous non-clinical applications. In a long-lasting effort to improve the detection ability of bioassays, functional nanomaterials have been actively explored to greatly enhance the sensitivity during the last two decades. This tutorial review focuses on recent progress in biosensor development by exploiting several unique optical, electronic and catalytic properties of a range of nanomaterials, such as gold nanoparticles, quantum dots, silicon nanowires, carbon nanotubes and graphene. In addition, a perspective on new opportunities offered by emerging technologies (e.g. DNA nanotechnology) is provided.

Based on the assay of DNA binding proteins upon visible light irradiation, a photoelectrochemical sensor was constructed for successfully probing a DNA–protein interaction for the first time.

Using CdS QD-tagged mercury-specific oligonucleotides, a novel folding-based photoelectrochemical sensor has been successfully fabricated for reagentless and highly sensitive Hg2+ detection.

Using the DNA bio-gate and duplex-specific nuclease assisted target recycling, a facile electrochemiluminescence assay was developed for the sensitive detection of survivin mRNA.

A dual target-recycling amplification strategy for sensitive detection of microRNAs based on duplex-specific nuclease and catalytic hairpin assembly was reported for the first time.

A new photoelectrochemical immunoassay for prostate-specific antigen (PSA) was successfully developed with high sensitivity via immunogold labeling.

An ideal nanoporous poly(N-isopropylacrylamide) membrane has been fabricated in glass microchannels by means of spatially controlled photopatterning technology for a high level of enrichment and cleanup of nucleic acids.

A ratiometric electrochemiluminescent biosensor for the detection of microRNAs based on cyclic enzyme amplification and distance dependent resonance energy transfer was reported for the first time.

A reusable potassium ion biosensor was reported for the first time based on the reversible DNA structural change and the interaction between surface plasmons of Au nanoparticles (NPs) and the ECL emission of CdS nanocrystals (NCs).

A new dual-functional electrochemical biosensor for the detection of prostate specific antigen (PSA) and telomerase activity was successfully developed based on a sandwich immunobinding format and telomerization assisted hemin–G-quadruplex-based DNAzyme as a biolabel.

Based on the amplified signal from SiO2@CdS nanocomposites integrated with K-doped graphene, a new electrochemiluminescence biosensor was developed for the successful detection of transcription factor TATA-binding protein (TBP).

Continuous CaCO3 hollow nanoparticle generation at room temperature with simultaneous molecule doping is realized on a liquid–gas dual phase microfluidic system.

Fingerprints are a unique characteristic of an individual. Recently, it has been realized that fingerprints carry more information about individuals than just their identity, for example, they may identify potential addicts and terrorists carrying explosives. Therefore, the development of imaging moieties capable of both fingerprint staining and drug/explosive visualization is of significant importance for forensic chemistry. Here we developed a nanohybrid comprising green- and red-emitting QDs for simultaneous fingerprint imaging and TNT visualization in fingerprints. The red-emitting Cu-doped ZnCdS (Cu–ZnCdS) QDs were embedded into silica nanoparticles and the green-emitting ZnCdS QDs were anchored onto the surface of the silica nanoparticles and further functionalized with polyallylamine (PAA). Both components of the nanohybrid, i.e., the PAA-functionalized green QDs and red QD-doped silica nanoparticles, could be explored for fingerprint imaging. Due to the formation of a Meisenheimer complex between TNT and PAA, the green-emitting QDs could be quenched by TNT, meanwhile the red-emitting QDs were inert. Therefore, the nanohybrid exhibited a traffic light-type fluorescence color change (green-yellow-red) to TNT concentration in the range of 40–400 μM. This method is promising for potential applications in security-screening needs in public areas such as airports and train stations.

With the rapidly increasing demands for ultrasensitive biodetection, the design and applications of functional nanoprobes have attracted substantial interest for biosensing with optical, electrochemical, and various other means. In particular, given the comparable sizes of nanomaterials and biomolecules, there exists plenty of opportunities to develop functional nanoprobes with biomolecules for highly sensitive and selective biosensing. Over the past decade, numerous nanoprobes have been developed for ultrasensitive bioaffinity sensing of proteins and nucleic acids in both laboratory and clinical applications. In this review, we provide an update on the recent advances in this direction, particularly in the past two years, which reflects new progress since the publication of our last review on the same topic in Chem. Soc. Rev. The types of probes under discussion include: (i) nanoamplifier probes: one nanomaterial loaded with multiple biomolecules; (ii) quantum dots probes: fluorescent nanomaterials with high brightness; (iii) superquenching nanoprobes: fluorescent background suppression; (iv) nanoscale Raman probes: nanoscale surface-enhanced Raman resonance scattering; (v) nanoFETs: nanomaterial-based electrical detection; and (vi) nanoscale enhancers: nanomaterial-induced metal deposition.