Xiaomei Chen

Advances in enzyme-free electrochemical sensors for hydrogen peroxide, glucose, and uric acid

AbstractEnzyme-free (also called non-enzymatic or direct) electrochemical sensors have been widely used for the determination of hydrogen peroxide, glucose, and uric acid. This review covers the recent progress made in this field. We also discuss the respective sensor materials which have strong effect on the electro-catalytic properties of the electrodes and govern the performance of these sensors. In addition, perspectives and current challenges of enzyme-free electrochemical sensors are outlined. Contains 142 references.n FigureIn the recent past, publications related to enzyme-free electrochemical sensors became plentiful. In this paper, we give an overview on the recent developments of enzyme-free sensors including hydrogen peroxide, glucose and uric acid sensors.

Green synthesis of graphene–PtPd alloy nanoparticles with high electrocatalytic performance for ethanol oxidation

A facile and green method is described for the fabrication of PtPd alloy nanoparticles on graphene nanosheets (PtPdNPs/GNs). The keys of the synthesis strategy were to employ a low-cost and green solvent, ethanol, as the reductant, and a two-dimensional carbon material, GNs, as the supporting material. The morphology, structure and composition of the as-prepared PtPdNPs/GNs were characterized by transmission electron microscopy (TEM), high resolution TEM, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It was found that by changing the preparation procedures and varying the molar ratio of the starting precursors, NPs with different shapes such as spherical NPs (Pt1Pd1NPs), nanoflowers (Pd@PtNFs) and nanodentrites (Pt3Pd1NPs) could be produced on GNs. Based on these observations, a plausible growth mechanism of PtPdNPs/GNs was discussed. In addition, the electrocatalytic properties of PtPdNPs/GNs for direct ethanol oxidation in alkaline media were systematically investigated. Due to the synergetic effects of Pt and Pd, and the enhanced electron transfer properties enhanced of GNs, PtPdNPs/GNs exhibited higher electrocatalytic ability and better tolerance to reaction intermediate poisoning in the electrooxidation of ethanol compared with Pt nanoflowers supported on GNs (PtNFs/GNs), PdNPs/GNs and PtPdNPs supported on carbon black (PtPdNPs/C). The presented method is a general, facile and green approach for the synthesis of GN-supported bimetallic PtM electrocatalysts, which is significant for the development of high performance electrocatalysts.

AuPd bimetallic nanoparticles decorated on graphene nanosheets: their green synthesis, growth mechanism and high catalytic ability in 4-nitrophenol reduction

A one-pot green method to synthesize ultrafine AuPd nanoparticles (NPs) monodispersed on graphene nanosheets (GNs) is reported. Due to the reducing capability, moderate number of deposition sites and large surface area, GNs are used as a three-functional agent such as reductant, stabilizer and support in this synthesis. The morphology, structure and composition of thus-prepared AuPdNPs/GNs were characterized by transmission electron microscopy (TEM), high resolution TEM, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. As it is a surfactant-free formation process, the as-prepared AuPdNPs/GNs are very clean and can exhibit a high activity towards the reduction of 4-nitrophenol. Moreover, the optical properties and catalytic activities of the AuPdNPs/GNs composite are tunable via controlling the Au versus Pd atomic ratio during their synthesis. The catalytic activity of bimetallic AuPdNPs/GNs composites is highly enhanced over the monometallic AuNPs/GNs and PdNPs/GNs composites. This straightforward method is of significance for deposition of bimetallic NPs with high catalytic performance on graphene-based materials.

Nonenzymatic sensing of glucose at neutral pH values using a glassy carbon electrode modified with graphene nanosheets and Pt-Pd bimetallic nanocubes

AbstractWe report on a nonenzymatic method for the determination of glucose using an electrode covered with graphene nanosheets (GNs) modified with Pt-Pd nanocubes (PtPdNCs). The latter were prepared on GNs by using N,N-dimethylformamide as a bifunctional solvent for the reduction of both metallic precursors and graphene oxide, and for confining the growth of PtPdNCs on the surface. The modified electrode displays strong and sensitive current response to the electrooxidation of glucose, notably at pHxa07. The sensitivities increase in the order of Pt1Pd5NCs< Pt1Pd3NCs< Pt5Pd1NCs< Pt3Pd1NCs< Pt1Pd1NCs. At an applied potential of +0.25xa0V, the electrode responds linearly (Ru2009=u20090.9987) to glucose in up to 24.5xa0mM concentration, with a sensitivity of 1.4xa0μAxa0cm−2xa0M−1. The sensor is not poisoned by chloride, and not interfered by ascorbic acid, uric acid and p-acetamidophenol under normal physiological conditions. The modified electrode also displays a wide linear range, good stability and fast amperometric response, thereby indicating the potential of the bimetallic materials for nonenzymatic sensing of glucose.n Figurenonenzymatic electrochemical method was developed for glucose determination using an electrode modified with PtPd nanocubes/graphene nanosheets (PtPdNCs/GNs). The new material shows a good performance in the sensing of glucose, thus is promising for the future development of nonenzymatic glucose sensors.

Au nanoparticles on citrate-functionalized graphene nanosheets with a high peroxidase-like performance.

In this paper, Au nanoparticles (AuNPs) have been homogeneously deposited on citrate-functionalized graphene nanosheets (Cit-GNs) by a simple one-pot reducing method. The morphology and composition of the thus-prepared AuNPs/Cit-GNs were characterized by transmission electron microscopy (TEM), high resolution TEM, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results showed that the AuNPs with a uniform size are well dispersed on the surface of the Cit-GNs. Significantly, the as-prepared AuNPs/Cit-GNs possess intrinsic peroxidase-like activity, which can catalyze the oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2) to develop a blue color in aqueous solution. The catalysis was in accordance with Michaelis-Menten kinetics and the AuNPs/Cit-GNs showed a strong affinity for both H2O2 and TMB. Moreover, by comparing with Cit-AuNPs, AuNPs/GNs and AuNPs/PVP-GNs, the AuNPs/Cit-GNs composite exhibits a higher catalytic ability with a lower Michaelis constant (Km) value, suggesting that the GNs with a large surface area and the citrate ions with more carboxyl groups around the AuNPs can greatly enhance the peroxidase-like activity of AuNPs/Cit-GNs. Taking the advantages of the high catalytic activity, the good stability and the low cost, the novel AuNPs/Cit-GNs represent a promising candidate as an enzyme mimic and may find a wide range of new applications in biochemistry and biotechnology.

Non-enzymatic oxalic acid sensor using platinum nanoparticles modified on graphene nanosheets

An enzyme-free oxalic acid (OA) electrochemical sensor was assembled using a platinum nanoparticle-loaded graphene nanosheets (PtNPGNs)-modified electrode. The PtNPGNs, with a high yield of PtNPs dispersed on the graphene nanosheets, were successfully achieved by a green, rapid, one-step and template-free method. The resulting PtNPGNs were characterized by transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and an X-ray diffraction technique. Electrochemical oxidation of OA on the PtNPGNs-modified electrode was investigated by cyclic voltammetry and differential pulse voltammetry methods. Based on the results, the modified electrode exhibited high electrochemical activity with well-defined peaks of OA oxidation and a notably decreased overpotential compared to the bare or even the GNs-modified electrode. Under optimized conditions, a good linear response was observed for the concentration of OA and its current response was in the range of 0.1-15 mM and 15-50 mM with a detection limit (S/N = 3) of 10 μM. Furthermore, the electrochemical sensor presented good characteristics in terms of stability and reproducibility, promising the applicability of the sensor in practical analysis.

Photoinduced enhancement of optical second harmonic generation in LiB3O5 nanocrystallites embedded between the Ag/ITO electrodes

It is reported that there is substantial enhancement of the optical second harmonic generation (SHG) at 1064xa0nm Nd:YAG laser wavelength for LiB3O5 nanocrystatllites embedded into the electric field aligned photopolymer oligoetheracrylate matrices. The borate nanocomposite was put between the electrodes containing Ag/ZnO NP with silver sizes 20, 40 and 60xa0nm. We study an influence of the Ag NP sizes on the output SHG. It is clearly seen that only excitation by the green continuous wave 532xa0nm laser with power about 350–400xa0mW with beam diameter about 4xa0mm give significant effect. The latter confirms a principal role of the surface plasmon resonances spectrally overlapped with the nonlinear excitations responsible for the observed changes of the SHG.