Kwok-Keung Shiu

Highly Sensitive Graphene–Pt Nanocomposites Amperometric Biosensor and Its Application in Living Cell H2O2 Detection

A sensitive hydrogen peroxide (H2O2) sensor was constructed based on graphene-Pt (RGO-Pt) nanocomposites and used to measure the release of H2O2 from living cells. The graphene and Pt nanoparticles (Pt NPs) were modified on glassy carbon electrode (GCE) by the physical adsorption and electrodeposition of K2PtCl6 solution, respectively. Through characterization by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), it was observed that the electrodeposited Pt NPs were densely covered and well distributed on the entire graphene surface. Electrochemical study demonstrates that the RGO-Pt nanocomposites modified glassy carbon electrode exhibited a high peak current and low overpotential toward the reduction of H2O2. The relevant detection limit of H2O2 is ∼0.2 μM with a wide linear range from 0.5 μM to 3.475 mM, displaying a much higher sensitivity (459 ± 3 mA M(-1) cm(-2), n = 5) than that of Pt nanoparticles or graphene modified electrode. This novel biosensor can measure the H2O2 release from living cells because of its low detection limit, wide linear range, and higher sensitivity.

Determination of uric acid at electrochemically activated glassy carbon electrode

A selective and sensitive electroanalytical method was developed for the determination of uric acid in urine samples. Uric acid was preconcentrated and electroanalyzed at electrochemically activated glassy carbon electrodes. No pretreatment of uric acid sample was necessary prior to electroanalysis. Linear response was observed over the range from 0.04 to 2.0 μM with a large slope of 55.6 A M−1 and a correlation of 0.999. The detection limit (3σ) was estimated to be about 9 nM.

Electroanalysis of copper species at polypyrrole-modified electrodes bearing alizarin red S ligands

Abstract Conducting polymer modified electrodes based on the incorporation of the anionic complexing ligand alizarin red S into polypyrrole (Ppy) film during electropolymerization were applied to the electroanalysis of metal species including Cu + and Cu 2+ . The copper species were readily extracted into the Ppy film electrode containing the complexing ligands and were determined electrochemically. The sensitivity for determination of Cu 2+ species was significantly better than that for Cu + species at much lower concentrations despite a smaller complex stability, but suffered from a very limited linear region. The results also showed that the ligand-to-metal ratios for complex formation at the Ppy film were concentration dependent.

Electrochemical quartz crystal microbalance studies on the electropolymerization processes of ortho-phenylenediamine in sulfuric acid solutions

Abstract The electropolymerization of ortho -phenylenediamine ( o -PD) in 0.10 M H 2 SO 4 , 0.10 M H 2 SO 4 +0.40 M Na 2 SO 4 , and 0.50 M H 2 SO 4 solutions was studied using an electrochemical quartz crystal microbalance. The poly-( ortho -phenylenediamine) (P o PD) films were formed during continuous potential cycling between −0.40 V and +0.95 V versus SCE. The decrease in the resonant frequency of the quartz crystals during electropolymerization of phenylenediamine demonstrated that the deposition of the polymer films occurred mainly in the potential range where the monomers were anodically oxidized. Dramatic changes in the resonant frequency and the resonant admittance were observed during the redox processes at potentials below +0.20 V. At least two kinds of deposits could be distinguished in the P o PD films. The surface concentration of the electroactive sites of the polymer prepared in 0.10 M H 2 SO 4 and in 0.10 M H 2 SO 4 +0.40 M Na 2 SO 4 solutions were much higher than that prepared in 0.50 M H 2 SO 4 . The acidity of the solution rather than the concentration of the anions of the electrolyte was found to have a strong influence on the electropolymerization processes. The results were discussed in the light of the effects of the solubilities of oligomers in solutions during the electropolymerization processes and the changes in the structures of the initially formed polymer films.

Voltammetric studies of electrochemical pretreatment of rotating-disc glassy carbon electrodes in phosphate buffer

Abstract Cyclic voltammetry was used to study the formation of graphite oxide film on the surface of rotating-disc glassy carbon electrodes. The film was formed by continuous potential cycling in phosphate buffer electrolyte. It was found that when cycling between the totally oxidized and totally reduced potential ranges (between + 2.3 and −1.2V vs. SCE), well-shaped redox peaks were obtained. Typical voltammograms comprised one cathodic and two anodic waves, where the anodic waves were directly related to the oxidation of surface-bound products associated with the cathodic process. All three processes were pH dependent. Freshly formed surface graphite oxide films were not stable and would undergo transformation to give the stable state upon potential cycling between potentials ± 1.0V. The ultimate stable voltammograms were characterized by two electrode processes. The quasi-reversible process involved surface quinone-like functional groups, while the other irreversible process might be related to the uptake and release of hydrogen ions at the porous graphite oxide film.

Voltammetric behavior of alizarin red S adsorbed on electrochemically pretreated glassy carbon electrodes

The electrochemical behavior of alizarin red S (dihydroxyanthraquinonesulfonate, ARS) adsorbed on electrochemically preanodized glassy carbon electrodes was studied by cyclic voltammetry. The adsorption of ARS was greatly enhanced by the electrochemical pretreatment of the electrodes. The central quinone functionalities of the adsorbed ARS underwent quasi-reversible reduction to give stable products. Oxidation of the dihydroxyl functionalities gave unstable products which underwent further follow-up chemical transformation to give new electroactive species. The products of the chemical transformation of the oxidized species could be further oxidized at a more positive potential, resulting in two pairs of quasi-reversible, quinone-like redox waves.

Electroanalysis of metal species at polypyrrole-modified electrodes

Abstract Conducting-polymer-modified electrodes based on the incorporation of two anionic ligands, namely bathophenanthroline disulfonate and bathocuproine disulfonate, into polypyrrole film during electropolymerization were found to show sensitivity to copper species (both Cu + and Cu 2+ ions). The copper species were readily extracted into the polypyrrole film electrode containing the complexing ligands. The electrochemical reaction of the incorporated copper complex resulted in a measurable square-wave voltammetric peak current, which was found to be related to the logarithm of copper concentrations. Reproducibility of the determination of copper species by the ligand-incorporated polypyrrole-modified electrodes was around ± 11% RSD and the detection limit was estimated to be about 2 μM.

Effects of polymer thickness on the potentiometric pH responses of polypyrrole modified glassy carbon electrodes

Abstract The potentiometric pH response of electropolymerized polypyrrole modified glassy carbon electrodes as a function of polymer film thickness was examined. Electrodes coated with thicker polypyrrole films showed mixed potentiometric responses toward both cationic and anionic species, while thinner polypyrrole films (

Preconcentration and Electroanalysis of Copper Species at Electrochemically Activated Glassy Carbon Electrodes

Electrochemically activated glassy carbon electrodes were applied to the preconcentration and electroanalysis of metal species. Activated glass y carbon electrodes were obtained by potentiostatic oxidation at þ2.0 V in 0.5 M sulfuric acid. Copper species were readily extracted onto the modified electrode and were determined electrochemically. Voltammetric peak currents showed linear response for copper concentrations in the range between 1 to 20 mM with a large slope of 2.11 A M and a correlation coefficient of 0.997. The reproducibility of the voltammetric measurements was found to be within 7 % RSD for five replicate measurements on copper concentration of 10 mM. The modified electrodes could be applied for repeated copper determinations without appreciable deterioration in electrode response. Results suggest that the preconcentratio n of copper species onto activated electrodes involved primarily cation-exchange interactions with the surface graphite oxide film.

Selective Determination of Vitamin B2 at Electrochemically Activated Glassy Carbon Electrode

Electrochemically activated glassy carbon electrodes were applied to the preconcentration and electroanalysis of Vitamin B2 (VB2) in multivitamin preparation. Voltammetric peak currents resulting from VB2 species adsorbed on activated electrodes showed linear response for VB2 concentrations in the range between 0.1 and 3.0 µM with a large slope of 12.2 A7emsp14;M–1 and a correlation coefficient of 0.996. The reproducibility of the voltammetric measurements was usually less than 7 % RSD for five replicate measurements. Common vitamin and metal species did not interfere in the determination.