Shou-Nian Ding

Colloidal laponite nanoparticles: Extended application in direct electrochemistry of glucose oxidase and reagentless glucose biosensing

The direct electron transfer (DET) between glucose oxidase (GOD) and the underlying glassy carbon electrode (GCE) can be readily achieved via colloidal laponite nanoparticles as immobilization matrix. Cyclic voltammetry of laponite/GOD/GCE, in anaerobic phosphate buffer solution (PBS, 0.1M, pH 5.0), showed a pair of stable and quasi-reversible peaks at potentials E(pa)=-0.372 V and E(pc)=-0.391 V vs. SCE, provoked by the prosthetic FAD group linked to the protein. The electrochemical reaction of laponite/GOD/GCE exhibited a surface-controlled process with the apparent heterogeneous electron transfer rate constant (k(s)) of 6.52 s(-1) and charge-transfer coefficient (alpha) of 0.5. The experiments of FTIR and UV-vis spectroscopy demonstrate that the immobilized GOD on colloidal laponite nanoparticles retained its native structure and its biocatalytic ability to its substrates. Based on the decrease of oxygen electrocatalytic signal, the proposed laponite/GOD/GCE was successfully applied in the reagentless glucose sensing at -0.45 V. The proposed electrode exhibited fast amperometric response (8s), broad linear range (2.0x10(-5)-1.9x10(-3) M), good sensitivity (4.8+/-0.5 mA M(-1) cm(-2)), low detection limit (1.0x10(-5) M) at a signal-to-noise ratio of 3, and excellent selectivity.

Reagentless biosensor for hydrogen peroxide based on self-assembled films of horseradish peroxidase/laponite/chitosan and the primary investigation on the inhibitory effect by sulfide.

Horseradish peroxidase (HRP) was successfully incorporated into the laponite/chitosan (Chit)-modified glassy carbon electrode (GCE) using step-by-step self-assembly. The self-assembly processes were monitored by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectra (EIS). Direct electrochemistry and electrocatalysis of the self-assembled HRP were investigated. Cyclic voltammetry of HRP/laponite/Chit/GCE, in anaerobic phosphate buffer solution (0.025 M PBS, pH 7.0), displayed a pair of stable and quasi-reversible peaks at potentials Epa=0.024 V and Epc=-0.132 V vs. SCE, attributed to the HRP-Fe(III)/HRP-Fe(II) redox couple. The electrochemical reaction of the HRP/laponite/Chit/GCE exhibited a surface-controlled electrode process. The electron transfer rate constant was estimated to be 1.82 s(-1). The self-assembled HRP maintained its biological activity and exhibited an excellent electrocatalytic performance for the reduction of H2O2 with fast amperometric response (10 s), broad linear range (2.9×10(-5) to 1.4×10(-3) M), good sensitivity (19.7±0.5 mA M(-1) cm(-2)) and low detection limit (5×10(-6) M) at a signal-to-noise ratio of 3. Moreover, the inhibitory of sulfide to the self-assembled HRP was also investigated.

Polycrystalline bismuth oxide films for development of amperometric biosensor for phenolic compounds

An attractive biocomposite based on polycrystalline bismuth oxide (BiO(x)) film and polyphenol oxidase (PPO) was proposed for the construction of a mediator-free amperometric biosensor for phenolic compounds in environmental water samples. The phenolic biosensor could be easily achieved by casting the biocomposite on the surface of glassy carbon electrode (GCE) via the cross-linking step by glutaraldehyde. The laboratory-prepared bismuth oxide semiconductor was polymorphism. Its hydrophilicity provided a favorable microenvironment for retaining the biological activity of the immobilized protein. The parameters of the fabrication process and the various experimental variables for the enzyme electrode were optimized. The proposed PPO/BiO(x) biosensor provided a linear response to catechol over a concentration range of 4 x 10(-9)M to 1.5 x 10(-5)M with a dramatically developed sensitivity of 11.3 AM(-1)cm(-2) and a detection limit of 1 x 10(-9)M based on S/N=3. In addition, the PPO/BiO(x) biocomposite was characterized by scanning electron microscope (SEM), Fourier transform infrared spectra (FTIR) and rotating disk electrode voltammetry.

Single-walled carbon nanotubes noncovalently functionalized by ruthenium(II) complex tagged with pyrene: electrochemical and electrogenerated chemiluminescence properties.

Ru being served: A pyrene-Ru/SWCNT nanohybrid was formed through noncovalent π-π stacking interactions (see figure). After oxidative treatment, the pyrene-Ru/SWCNT-functionalized Pt electrode achieved a highly reversible redox process and exhibited excellent electrogenerated chemiluminescence behavior.

Xanthine oxidase/laponite nanoparticles immobilized on glassy carbon electrode: Direct electron transfer and multielectrocatalysis

In this work, colloidal laponite nanoparticles were further expanded into the design of the third-generation biosensor. Direct electrochemistry of the complex molybdoenzyme xanthine oxidase (XnOx) immobilized on glassy carbon electrode (GCE) by laponite nanoparticles was investigated for the first time. XnOx/laponite thin film modified electrode showed only one pair of well defined and reversible cyclic voltammetric peaks attributed to XnOx-FAD cofactor at about -0.370 V vs. SCE (pH 5). The formal potential of XnOx-FAD/FADH(2) couple varied linearly with the increase of pH in the range of 4.0-8.0 with a slope of -54.3 mV pH(-1), which indicated that two-proton transfer was accompanied with two-electron transfer in the electrochemical reaction. More interestingly, the immobilized XnOx retained its biological activity well and displayed an excellent electrocatalytic performance to both the oxidation of xanthine and the reduction of nitrate. The electrocatalytic response showed a linear dependence on the xanthine concentration ranging from 3.9 x 10(-8) to 2.1 x 10(-5)M with a detection limit of 1.0 x 10(-8)M based on S/N=3.

TiO2 nanocrystals electrochemiluminescence quenching by biological enlarged nanogold particles and its application for biosensing

Electrochemiluminescence (ECL) of TiO(2) nanocrystals with different crystal styles modified fluorine-doped tin oxide (FTO) electrode was investigated in H(2)O(2) solution. The amorphous TiO(2) nanospheres were facilely synthesized by the hydrothermal and condensation method. Crystal TiO(2), namely anatase and rutile, were prepared by calcination of the amorphous TiO(2) nanospheres at 450 and 800°C, respectively. The transmission electron microscope (TEM) and electron diffraction pattern were used to characterize the obtained TiO(2) nanoparticles morphology and the corresponding crystal styles. The electrochemical and ECL behaviors were investigated by cyclic voltammetry. The ECL quenching was observed by introduction of gold nanoparticles. Based on the quenching effect, a sensitive glucose ECL biosensor as a model was fabricated by in-situ growing-up gold seeds in AuCl(4)(-) solution induced by biologically generated H(2)O(2). The linear range to detect glucose is from 5.0×10(-7)M to 4.0×10(-3)M with the limit of detection of 2.5×10(-7)M.

Label-free detection of sulfide ions based on fluorescence quenching of unmodified core–shell Au@Ag nanoclusters

Based on the principle of fluorescence quenching, by the interaction between S2− ions and the Ag atoms/ions on the surface of the core–shell Au@Ag NCs, we propose a simple label-free method for the detection of S2− ions with high selectivity and sensitivity by using fluorescent core–shell Au@Ag NCs in aqueous media.

A promising biosensing-platform based on bismuth oxide polycrystalline-modified electrode: Characterization and its application in development of amperometric glucose sensor

Nano-structured bismuth oxide (nano-BiOx) is a suitable material for enzyme immobilization owing to its attractive properties, such as large specific surface area, suitable permeability of the resulting film, the high biocompatibility, and as well as photovoltaic effect from semiconductor nanoparticles. Thus, a new type of amperometric glucose biosensor based on nano-BiOx was constructed. The amperometric detection of glucose was assayed by potentiostating the GOD/nano-BiOx electrode at 0.5 V to oxidize the enzymatically generated hydrogen peroxide. The proposed biosensor provided a linear response to glucose over a concentration range of 1 x 10(-6) M to 1.5 x 10(-3) M with a sensitivity of 51.0+/-0.4 mA/(M cm(2)) and a detection limit of 4 x 10(-7) M based on S/N=3. The apparent Michaelis-Menten constant was calculated to be 2.9 x 10(-3) M. In addition, characterization of nano-BiOx and modified electrode was performed by FT-IR spectroscopy, Raman spectroscopy, scanning electron microscope (SEM) and rotating-disk electrode (RDE) voltammetry.

Study of Al doping effect on superconductivity of Mg1−xAlxB2

Mg1−xAlxB2 samples in the region of 0<x⩽0.6 were prepared to study the effect of Al doping on superconductivity of MgB2. The samples were synthesized by the common solid reaction method and their structures were examined by x-ray diffraction, which shows the obvious Al effect on the interplane boron sheet separation. By means of resistivity-temperature (R-T) and ac susceptibility-temperature (χ-T) measurements, we investigated the superconductivity of the samples with different levels of Al doping. It was found that the sample persisted its bulk superconductivity until x=0.6, which was also confirmed by the critical temperature Tc at different levels of Al determined by χ-T and R-T measurements.

Biosensing platform based on graphene oxide via self-assembly induced by synergic interactions

A novel self-assembled glucose biosensor based on graphene oxide (GO) was constructed by using 1-pyrenebutyric acid-N-hydroxysuccinimide ester (PANHS) as linking molecular. The stepwise self-assembly process was performed for PANHS anchoring in N,N-dimethylformamide (DMF) solvent and the further glucose oxidase (GOD) binding in aqueous solution, respectively. The molecular interactions and the morphologic properties were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electronic microscopy (FESEM), and atomic force microscopy (AFM). In addition, the quantitative loadings of anchored PANHS and GOD were well elucidated by surface plasmon resonance (SPR) measurements. The obtained novel glucose sensor exhibited satisfactory analytical performance to glucose: wide linear range (4.0×10(-6) to 4.4×10(-3) M), fast response (10s), high sensitivity (40.5±0.4 mA M(-1) cm(-2)), and low detection limit (2 μM, S/N=3). Furthermore, the biosensor exhibited excellent long-term stability and satisfactory reproducibility.