•An AA novel ratiometric biosensor based on PCN-333 (Al) MOFs-KB-Thi was prepared.•PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface.•PCN-333 (Al) MOFs could selectively accumulate target analytes into their pores to enhance the selectivity.•The ratometric biosensor could improve the accuracy and reproducibility.•The AA ratiometric biosensor showed good performance toward AA detection.In this work, a novel ascorbic acid (AA) ratiometric biosensor was prepared by using the PCN-333 (Al) metal-organic frameworks (MOFs) (PCN stands for porous coordination network) to encapsulate Ketjen black (KB) as catalyst for catalyzing oxidation of AA and thionine (Thi) as an internal reference signal simultaneously. The encapsulation of KB and Thi in the pores of PCN-333 (Al) MOFs not only improved efficiency of KB and Thi greatly because PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly. Furthermore, PCN-333 (Al) MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors. The oxidation peak current of AA catalyzed by KB at −0.05 V increased with the increasing concentration of AA, while the oxidation peak current of Thi at −0.24 V kept constant, which resulted in a novel ratiometric biosensor for AA detection. The ratiometric biosensor exhibited a wider linear range from 14.1 ± 0.2 to (5.5 ± 0.1) х103 μM (R2 = 0.998) and a lower detection limit of 4.6 ± 0.1 μM with high accuracy, selectivity, reproducibility and sensitivity. The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.

•A novel ternary hybrid rGO-Ag wrapped by polydopamine (rGO-Ag@PDA) was prepared.•RGO-Ag@PDA displays stronger adsorption ability to dyes than that of rGO-Ag.•RGO-Ag@PDA shows much higher SERS activity than that of rGO-Ag.•RGO-Ag@PDA also exhibits enhanced stability and improved reusability.•Sensitive detection of aromatic dyes are achieved on rGO-Ag@PDA.A novel hybrid of reduced graphene oxide-silver nanoparticle composite (rGO-Ag) wrapped by a thin layer of polydopamine (PDA) (rGO-Ag@PDA) was prepared as a highly active substrate for surface enhanced Raman scattering detection of aromatic dyes. rGO-Ag prepared by one-pot citrate reduction was coated with PDA through the self-polymerization of dopamine to produce the rGO-Ag@PDA hybrid. The morphology, component, absorption ability and SERS activity of the products were characterized by SEM, EDS, FTIR, UV–vis absorption, and Raman spectroscopy. Due to the PDA coating, the rGO-Ag@PDA hybrid shows enhanced adsorption ability to the dye molecules, and subsequently leads to stronger SERS signal of dyes than that obtained on widely reported rGO-Ag hybrid substrate. SERS detection of crystal violet, methylene blue, and malachite green on the rGO-Ag@PDA can be down to 0.1 nM, 0.1 μM and 1 nM, respectively. Moreover, the rGO-Ag@PDA also displayed enhanced stability and improved recyclability than those of rGO-Ag. The proposed substrate may be used for SERS analysis and environmental monitoring.Reduced graphene oxide-silver nanoparticle wrapped by a thin layer of polydopamine (rGO-Ag@PDA) was prepared as a SERS substrate for aromatic dye detection. This novel substrate shows stronger absorption ability to dyes, higher SERS activity, increased stability and improved reusability than those of widely reported rGO-Ag hybrid substrate.

•A novel on-off ratiometric electrochemical biosensor was developed for glucose detection.•The AuNPs-GOD was used to catalyze the oxidation of glucose and the reduction of O2.•Thionine was used to catalyze the reduction of produced H2O2 as an inner reference signal.•The proposed on-off ratiometric electrochemical biosensor showed good performances.A highly selective and accurate on-off ratiometric electrochemical biosensor to detect glucose was proposed based on gold nanoparticles (AuNPs)-glucose oxidase (GOD) nanocomposites as the catalyst for both the oxidation of glucose and the electrochemical reduction of O2 and the thionine as the inner reference signal for the first time. The reduction peak of O2 catalyzed by AuNPs-GOD at −0.45 V decreased in GOD-glucose reaction in which the O2 was consumed gradually to produce H2O2. While, the reduction peak of the produced H2O2 catalyzed by thionine at −0.24 V increased gradually. By using the ratiometric peak current as detection signal, a novel on-off ratiometric electrochemical biosensor for glucose detection was developed and exhibited an acceptable detection limit of 11.66 μM and a wide linear range from 35.43 μM to 15 mM. The biosensor also exhibited high accuracy, high selectivity, good reproducibility and high sensitivity. The ratiometric electrochemical approach not only developed a new method for highly selective and accurate detection of glucose but also provided a good idea for accurate and selective analysis of other analytes.Download high-res image (133KB)Download full-size image

In this study, a polyoxometalate (POM) and graphene oxide (GO) were hydrothermally treated to form a novel three-dimensional (3D) macroporous hybrid 3D-mp-rGO–POM for nitrite sensing. Scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and electrochemical methods were used to characterize the hybrid. The 3D porous rGO not only obviously enhances the conductivity and largely increases the active surface area, but also greatly facilitates the mass transport and efficiently decreases the leaching of the POM from the modified electrode. The synergistic interaction between the POM and 3D porous rGO endows 3D-mp-rGO–POM with a highly stable and efficient electrocatalytic activity towards the oxidation of nitrite. A nonenzymatic sensor for nitrite based on this hybrid shows two linear response ranges of 0.5 μM to 221 μM and 0.221 mM to 15.221 mM, with a detection limit of 0.2 μM (S/N = 3), which displays higher sensitivity, higher stability, a wider linear range and a lower detection limit than sensors based on POMs or 2D-rGO supported POM hybrids. Interference from H2O2 was effectively avoided by monitoring the oxidation current of nitrite instead of its reduction current. The 3D-mp-rGO–POM hybrid with facile preparation, high stability and good catalytic activity may have promising applications in catalysis, sensors, and so on.

•A low cost, highly efficient 3D SERS substrate AgNSs@PANI(A low cos)/3D-CF was prepared.•Polyaniline was used as medium and reductant for silver nanosheet growth.•Succinic acid is vital to control the morphology of silver nanostructure.•The AgNSs@PANI-3D-CF shows strong absorption to target molecules.•Molecule sensing on AgNSs@PANI/3D-CF by SERS down to 0.1 nM.In this study, a new plasmonic hybrid AgNSs@PANI/3D-CF composed of interlaced silver nanosheets (AgNSs) grown on polyaniline (PANI) nanobars decorated three dimensional macroporous carbon foam (3D-CF) was prepared for molecule sensing by surface enhanced Raman scattering (SERS). The morphology, component, adsorption ability and SERS activity of the hybrid were characterized by SEM, EDS, FTIR, XRD, UV–vis absorption spectrum, and Raman spectroscopy. Controlling the silver growth time and introduction of succinic acid are vital to obtain the interlaced silver nanosheets fully covered 3D scaffold. The porous structure and large surface area of the hybrid bring it a high adsorption ability to dye molecules. And interlaced AgNSs endow the hybrid with dense hot-spots for highly efficient SERS detection. The lowest SERS detectable concentration of 4-mercaptobenzoic acid (4-MBA), Nile blue (NB) and Methylene blue (MB) on AgNSs@PANI/3D-CF was 0.1 nM, 0.1 nM and 10 nM, respectively. A good result was also achieved for NB detection in real water sample. The proposed hybrid with unique structure, high Raman enhancement ability and good reproducibility may find promising applications in environment monitoring, optical sensing and so on.Download high-res image (123KB)Download full-size image

•A novel electrochemical immunosensor has been developed for CEA biomarker detection.•The integrated 3D-KSCs electrode was used as signal collector.•AuNPs-Ab2- GOD- Con A was used as immunosensing probe.•The proposed immunsensor could high-sensitively detect CEA with satisfactory reproducibility and stability and acceptable reliability.A novel pH-dependent immunosensor to detect tumor biomarker, carcinoembryonic antigen (CEA), was developed by using the pH-dependent AuNPs-Ab2-glucose oxidase-Concanavalin A as tracing tag and the albumin bovine V-Ab1/chitosan-AuNPs/three-dimensional kenaf stem-derived macroporous carbon (3D-KSCs) integrated electrode as signal collector based on a sandwich-type assay mode. The integrated 3D-KSCs electrode provided a large specific surface area to load a large number of Ab1 effectively and the tracing tag with a lots of pH-dependent surface negative charges repulsed the negatively charged probe of Fe(CN)63− in a pH 9.0 solution. Accordingly, after a sandwich immunoreaction, the quantitative capture of tracing tag on the signal collector greatly hindered the electron transfer of Fe(CN)63−/4− due to the electrostatic repulsion, which improved the sensitivity and selectivity of the immunosensors significantly. It was verified by electrochemical impedance spectroscopy. The resistance to charge transfer of Fe(CN)63−/4− changed proportionally toward CEA concentration from 4 pg mL −1 to 50 ng mL −1 with a low detection limit of 1.3 pg mL −1 (S/N = 3) and a high sensitivity of 57.57 Ω ng−1 mL. Based on human serum experiments, the sensing platform was proved to be suitable to assay CEA in a practical biosystem. This work not only gives a sensitive way to detect CEA but also provides a potential strategy for immunosensors based on 3D-KSC electrode and pH-dependent behavior.

In this study, a sensitive hydrazine sensor based on CuxO decorated three dimensional poly(3,4-ethylene-dioxythiophene) (3D-PEDOT) was developed. A 3D-PEDOT–CuxO hybrid was prepared through a facile electrochemical deposition and cyclic voltammetry treatment process. The hybrid material was characterized by scanning microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Raman, and electrochemical methods. It was found that 3D-PEDOT not only acts as a matrix to increase the loading amount of CuxO and enhances the conductivity, but also directly contributes to the catalytic oxidation of hydrazine. Owing to the synergistic interaction between 3D-PEDOT and CuxO, the 3D-PEDOT–CuxO hybrid displayed obviously enhanced catalysis for hydrazine oxidation with lower overpotential and stronger oxidation current compared to single component CuxO or 3D-PEDOT. The hydrazine sensor based on the 3D-PEDOT–CuxO hybrid exhibited a one order of magnitude wider linear range (0.5 μM to 53 mM), ten-fold lower detection limit (0.2 μM) and higher stability compared to those of the sensor based on CuxO. The proposed sensor was also used for the determination of hydrazine in real water samples with a satisfactory recovery.

•Facile preparation of PDDA modified rGO within 30 min for nitrite sensing.•PDDA-rGO shows high stability and dispersity in water and large surface area.•Much enhanced catalysis for nitrite oxidation than that of rGO or bare GCE.•Detection of nitrite with performance better than that of graphene based hybrids.In this communication, a sensitive electrochemical nitrite sensor was constructed based on poly (diallyldimethylammonium chloride) (PDDA) functionalized reduced graphene oxide (PDDA-rGO). The preparation of PDDA-rGO is quite facile, and the PDDA-rGO exhibits good dispersity and high stability in water, together with good conductivity and positive surface charge. All these factors lead to a greatly enhanced catalysis of PDDA-rGO for the nitrite oxidation compared with that of unmodified rGO or bare glassy carbon electrode. Based on PDDA-rGO, an electrochemical nitrite sensor with low overpotential (0.75 V), wide linear range (0.5 μM–2 mM), low detection limit (0.2 μM), good stability and selectivity was fabricated, which exhibited satisfied recovery for detecting nitrite in drinking water.

In this study, a ternary nanocomposite Au –MnO2–rGO composed of gold nanoparticles (Au NPs), manganese dioxide nanorods (MnO2 NRs) and reduced graphene oxide nanosheet (rGO) was synthesized for the catalytic reduction and nonenzymatic sensing of hydrogen peroxide (H2O2). The composite Au–MnO2–rGO was characterized by SEM, TEM, XRD and electrochemical methods. It was found the integration of MnO2 NRs with rGO could enhance the attachment of MnO2 NRs on the electrode and improve its conductivity. Subsequent decoration of Au NPs, further improved the performance for the reduction of H2O2. Greatly enhanced catalysis was observed on the ternary nanocomposite due to the synergistic interactions among MnO2 NRs, rGO and AuNPs. Based on this Au–MnO2–rGO composite, a new nonenzymatic H2O2 sensor with a wide linear range (0.1–22 μM and 0.022–12.6 mM), low detection limit (0.05 μM), high sensitivity (980 μA/mM/cm2), good stability and negligible interference from ascorbic acid was successfully fabricated.

In this paper, three approaches including physical adsorption, in situ reduction, and one pot synthesis were developed to fabricate cuprous oxide–reduced graphene oxide (Cu2O–rGO) nanocomposites. These nanocomposites were characterized by XRD, SEM, Raman spectrum and electrochemical methods. The composite with different morphologies and components fabricated from these three methods displayed much enhanced performance for the catalytic reduction of H2O2 than the single component Cu2O. Among these Cu2O–rGO nanocomposites, the product prepared through the simple physical adsorption approach (i.e. Cu2O–rGOpa) showed a slightly better performance than the other two composites. A wider linear range (0.03–12.8 mM), higher sensitivity (19.5 μA/mM) and better stability were achieved on the Cu2O–rGOpa based sensor than Cu2O based sensor for accurate detection of H2O2.

Carbon nanofibers (CNFs) decorated by manganese dioxide nanoparticles (MnO2NPs) are prepared by an electrospinning technique, followed by thermal treatments in different environments. The obtained MnO2NPs–CNFs composite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). SEM images showed that the surface of the CNFs was decorated with homogeneously dispersed nanoparticles with narrow size distribution. XRD and XPS characterizations confirmed the main composition of the nanoparticles was MnO2. Furthermore, for the strong catalytic oxidation ability of MnO2 toward hydrogen peroxide, the composite material was used as the matrix for nonenzymatic sensor construction. Cyclic voltammetry and amperometric response were applied to investigate the performance of the sensor. Under the optimum conditions, a wide linear range from 10 μM to 15 mM (R = 0.9994, R represents the correlation coefficient) with a low detection limit of 1.1 μM was obtained. The proposed sensor also displayed short response time, high sensitivity, good reproducibility and stability. These superior performances could be attributed to the large surface area and excellent electrocatalytic activity of the MnO2NPs–CNFs.

The Fe3O4–graphene oxide (Fe3O4–GO) nanocomposites were prepared by a chemical co-precipitation of FeSO4, FeCl3,·NH3·H2O and GO. The Fe3O4–GO was characterized by scanning electron microscopy, X-ray powder diffraction, thermogravimetric analysis and electrochemical method. The results showed that ultrafine Fe3O4 nanoparticles was prepared and densely assembled on GO nanosheets. The Fe3O4–GO exhibits large surface area and high catalysis towards the oxidation of cysteine and N-acetyl cysteine, which could be used for cysteine and N-acetyl cysteine sensing with a wide linear range (0.5–13.5 mM for cysteine and 0.12–13.3 mM for N-acetyl cysteine) and low detection limit (56 μM for cysteine and 25 μM for N-acetyl cysteine). The excellent catalytic activity, high sensitivity and good stability made such Fe3O4–GO nanocomposites to be promising nanomaterials for constructing nonenzymatic sensor.Highlights► Fe3O4–GO nanocomposites are prepared. ► Fe3O4–GO exhibits high catalysis towards the oxidation of cysteine and N-acetyl cysteine. ► Mediating Fe3O4–GO on a glassy carbon electrode developed an electrochemical sensor. ► The sensor showed high selectivity and stability.

Carbon nanofibers (CNFs) decorated with cobalt nanoparticles (CoNPs) were synthesized by a two-step procedure consisting of electrospinning and thermal treatment. The CoNPs–CNFs hybrid materials were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction spectrum, which showed that the CoNPs were of the cubic phase and well dispersed on the surface of CNFs. The electrochemical behaviors and electrocatalytic performances towards the oxidation of the amino acids at the CoNPs–CNFs modified glassy carbon electrode (GCE) were evaluated. The results indicated that the CoNPs–CNFs showed good electrocatalytic activity towards the oxidation of cysteine and N-acetyl cysteine, and the current response of the CoNPs–CNFs/GCE was sensitive to pH of the electrolyte solution. The peak current was quite large at pH 13.0 but greatly suppressed at pH 7.5, suggesting that the electrode can realize pH-controlled oxidation of amino acids. The good catalytic activity, well conductivity and high stability made the CoNPs–CNFs promising materials for constructing an enzymeless sensor.

A sensitive, fast and cheap sensor for quantitative determination of carbaryl pesticide using amperometric acetylcholinesterase (AChE) biosensor based on prussian blue (PB)–chitosan (CHIT) hybrid film was reported. This biosensor was fabricated by firstly electrodepositing PB–CHIT hybrid film on glassy carbon electrode (GCE) and subsequently assembling AChE on PB–CHIT hybrid film. The PB–CHIT hybrid film exhibited a good biocompatibility with AChE and effectively immobilized AChE on it. Nanosized PB uniformly distributed in the PB–CHIT hybrid films and showed a good electrocatalytic activity toward oxidation of thiocholine, which was a product from the hydrolysis of acetylthiocholine catalyzed by AChE. The oxidation potential of thiocholine was decreased from 0.68 V to 0.32 V and accordingly the sensitivity of biosensor was largely improved. The inhibition of carbaryl on the activity of AChE was proportional to carbaryl concentration in the ranges from 0.01 to 0.4 μM and from 1.0 to 5.0 μM with the correlation coefficients of 0.9996 and 0.9997, respectively. The detection limit was calculated to be about 3 nM. The biosensor provided a new promising tool for pesticide analysis.

Cytochrome c (Cyt c) was successfully immobilized on poly(ferrocenylsilane)–DNA (PFS–DNA) composite film modified gold electrode by electrostatic adsorption. The direct electron transfer of Cyt c in the composite film modified electrode and its application as hydrogen peroxide (H2O2) biosensor were investigated. The results suggested that Cyt c could be effectively immobilized in the PFS–DNA composite modified electrode. The adsorbed Cyt c showed a good electrochemical activity with a pair of quasi-reversible redox peaks in 0.20 M, pH 7.0 phosphate buffer solution. PFS–DNA composite films showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c also exhibited a good electro-catalytic activity towards the reduction of H2O2. The catalytic current increased linearly to the H2O2 concentration in a range of 3.0 μM–1.83 mM (r = 0.999; n = 19) and the detection limit was calculated to be 0.72 μM based on the criterion of a signal-to-noise ratio of 3. Based on the novel construction, a third-generation biosensor could be obtained for the determination of H2O2.

The adsorption of 3,3′′′-dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (4T) molecules on an Au(111) electrode was examined by using in situ scanning tunneling microscopy in 0.10 M HClO4, revealing internal molecular structures of the tetrathiophene backbones and the hexyl side chains. The 4T admolecules were packed in lamellae with their molecular axis aligned along the main axis of the Au(111) substrate and their hexyl side chains interdigitated to enhance intermolecular interaction. Dynamics of molecular organization incurred by the shifting of potential was also observed in this study. By examining and comparing the adsorption of 4T on HOPG and Au(111), we address the role of the substrate in understanding the arrangement of 4T admolecules.

A monolayer of Keggin-type heteropolyanion [SiNi(H2O)W11O39]6− was fabricated by electrodepositing [SiNi(H2O)W11O39]6− on cysteamine modified gold electrode. The monolayer of [SiNi(H2O)W11O39]6− modified gold electrode was characterized by atomic force microscopy (AFM) and electrochemical method. AFM results showed the [SiNi(H2O)W11O39]6− uniformly deposited on the electrode surface and formed a porous monolayer. Cyclic voltammetry exhibited one oxidation peak and two reduction peaks in 1.0 M H2SO4 in the potential range of −0.2 to 0.7 V. The constructed electrode could exist in a large pH (0–7.6) range and showed good catalytic activity towards the reduction of bromate anion (BrO3−) and nitrite (NO2−), and oxidation of ascorbic acid (AA) in acidic solution. The well catalytic active of the electrode was ascribed to the porous structure of the [SiNi(H2O)W11O39]6− monolayer.

Silver (Ag) electrodes were roughened by electrochemical oxidation–reduction cycles (ORC) in a KCl solution. The roughened Ag electrode exhibited a powerful electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). Atomic force microscopy and electrochemical experiments confirmed that the electrocatalytic ability mainly resulted from the Ag nanoparticles produced in the process of ORC on the roughened Ag electrode. The electrochemical behaviors of the roughened Ag electrodes toward the reduction of H2O2 and the factors related to that reduction were investigated in detail.