A hydrogen peroxide biosensor combined HRP doped polypyrrole with ferrocene modified sol-gel derived composite carbon electrode

A novel amperometric biosensor for the detection of hydrogen peroxide is described. The biosensor was constructed by electrodepositing HRP/PPy membrane on the surface of ferrocenecarboxylic acid mediated sol-gel derived composite carbon electrode. The biosensor gives response to hydrogen peroxide in a few seconds with detection limit of 5x10(-7) mol (.) L-1 (based on signal : noise=3). Linear range is up to 0.2 mmol (.) L-1.

Surface-renewable cobalt(II) hexacyanoferrate-modified graphite organosilicate electrode and its electrocatalytic oxidation of thiosulfate

Cobalt(II) hexacyanoferrate (CoHCF) was deposited on graphite powder by an in situ chemical deposition procedure and then dispersed into methyltrimethoxysilane-derived gels to prepare a surface-renewable CoHCF-modified electrode. The electrochemical behavior of the modified electrode in different supporting electrolyte solutions was characterized by cyclic voltammetry. In addition, square-wave voltammetry was employed to investigate the pNa-dependent electrochemical behavior of the electrode. The CoHCF-modified electrode showed a high electrocatalytic activity toward thiosulfate oxidation and could thus be used as an amperometric thiosulfate sensor.

Amperometric determination of thiosulfate at a surface-renewable nickel(II) hexacyanoferrate-modified carbon ceramic electrode

Graphite powder-supported nickel(II) hexacyanoferrate (NiHCF) was prepared by the in situ chemical deposition method and then dispersed into methyltrimethoxysilane-derived gels to form a conductive composite. The composite was used as electrode material to construct a surface-renewable three-dimensional NiHCF-modified carbon ceramic electrode. Electrochemical behavior of the chemically modified electrode was well characterized using cyclic and square-wave voltammetry. The electrode presented a good electrocatalytic activity toward the oxidization of thiosulfate and thus was used as an amperometric sensor for thiosulfate in the photographic waste effluent. In addition, the electrode exhibited a distinct advantage of surface-renewal by simple mechanical polishing, as well as simple preparation, good chemical and mechanical stability. (C) 2001 Elsevier Science B.V. All rights reserved.

Electrochemical preparation and characterization of silicotungstic heteropolyanion monolayer electrostatically linked aminophenyl on carbon electrode surface

In this paper, an organic-inorganic composite film of heteropolyanion was Formed by attaching a Keggin-type heteropolyanion, SiW12O404-, on carbon electrode surface derivatized by 4-aminophenyl monolayer. The composite film thus grafted on carbon electrode surface has good stability because of the ionic bonding character between SiW12O404- and surface aminophenyl groups. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used to characterize the composite film. Compared with SiW12O404- electrodeposited on a bare glassy carbon electrode (GCE), the composite film gives three more sharp and well-defined redox couples attributed to two one- and two-electron processes, and the analyses of the voltammograms of SiW12O404- anion in the composite film modified on GCE shows that its surface coverage is close to a closest packing monolayer. STM characterization shows that a two-dimensional order heteropolyanion monolayer was formed on HOPG substrate. The composite film provides a favorable environment for electron and proton transfer between SiW12O404- ion and electrode surface, which may make it suitable for various applications in sensors and microelectronics devices.

Potential-dependent adsorption/desorption of organic adsorbate at HOPG electrode and accompanying delamination of graphite surface

In situ electrochemical scanning tunneling microscopy, alternating current voltammetry, and electrochemical quartz crystal microbalance have been employed to follow the potential-dependent adsorption/desorption processes of nucleic acid bases on highly oriented pyrolytic graphite (HOPG) electrode. The results show that (i) potential-dependent adsorption/desorption of nucleic acid bases on HOPG electrode was accompanied by delamination of the HOPG surface, and the delamination initiates from steps or kinks on the electrode surface, which provide highly active sites for adsorption; (ii) the delamination usually occurred when the electrode potential was changed or when the electrode was at potentials where the phase transition of adsorbate occurred. These results suggest that the surface stress resulting from the interaction between the substrate and adsorbate, as well as the interaction due to potential-induced surface charge distribution and the hysteresis of charge equilibrium are the main factors resulting in HOPG delamination. (C) 1999 The Electrochemical Society. S0013-4651(97)12-013-4. All rights reserved.

Preparation of a composite film electrode containing 12-tungstosilicic acid and its electrocatalytic reduction for nitrite

A novel organic-inorganic composite film was formed by attaching Keegin-type heteropolyanion, SiW12O404- (devoted briefly as SiW12), on a glassy carbon electrode derivatized by 4-aminophenyl group. The composite film has an ionic bonding character between SiW12 and the surface amino group, which greatly improves the Blm stability and exhibits a more reversible electrochemical behavior. The modified electrode offers an excellent and stable electrocatalytic response for the reduction of nitrite. Possible mechanism was provided for the reaction of nitrite with SiW12O404-/aminophenyl composite film.

Self-gelatinizable copolymer immobilized glucose biosensor based on Prussian Blue modified graphite electrode

A novel poly(vinyl alcohol) grafting 4-vinylpyridine self-gelatinizable copolymer was adapted to immobilize glucose oxidase. The reduction of hydrogen peroxide (H2O2) was detected at a Prussian Blue (PB) modified graphite electrode. A stable and sensitive glucose amperometric biosensor is described. The copolymer is a good biocompatible polymer in which the glucose oxidase retains high activity. Moreover, the copolymer can adhere firmly to the inorganic PB membrane. The sensor showed an apparent Michaelis-Menten constant of 18 +/- 0.2 mM and a maximum current density of 1.14 mu A cm(-2) mM(-1). The linear range is from 5 mu M to 4.5 mM glucose and the detection limit is 0.5. mu M glucose. The catalytic efficiency of PB for the reduction of H2O2 is higher than that for the oxidation of H2O2. Glucose concentrations in serum samples from healthy persons and diabetic patients were determined using the sensor. The results compared well with those provided by the hospital using a spectroscopy method.

Irreversible capacity loss of graphite electrode in lithium-ion batteries

The irreversible capacity loss of the carbon electrode in lithium-ion batteries at the first cycle is caused mostly by surface film growth. We inspected an unknown irreversible capacity loss (UICL) of the natural graphite electrodes. The charge/discharge behavior of graphite and meso-phase carbon microbeads heat-treated at 2800 degrees C (MCMB28) as the materials of the carbon anode in the lithium-ion battery were compared. It was found that the capacity loss of the natural graphite electrode in the first cycle is caused not only by surface film growth, but also by irreversible lithium-ion intercalation on the new formed surface at the potential range of lithium intercalation, while the capacity loss of the MCMB28 electrode is mainly originated from surface film growth. The reason for the difference of their irreversible capacity losses of these two kinds of carbon material was explained in relation to their structural characteristics. (C) 1997 Published by Elsevier Science S.A.

VOLTAMMETRY OF CYTOCHROME-C ENTRAPPED IN HYDROGEL MEMBRANE ON GRAPHITE ELECTRODE

The voltammetric behavior of cytochrome c entrapped in hydrogel membranes at paraffin wax-impregnated spectroscopic graphite electrodes (WISGE) was studied in this paper. A pair of well-defined peaks appeared at +70 mV (vs. Ag/AgCl). Beside these two peaks, another pair of peaks emerged at around +225 mV. Further investigations suggested that at least three states of cytochrome c existed in the membranes due to the special structure of the hydrogel. The native conformation of cytochrome c molecules was stabilized by the hydrophilic environment that was formed by the hydroxyl structure of the membranes and facilitated the cytochrome c electron transfer reaction at +70 mV. The molecules directly adsorbed on the surface of the graphite electrode were responsible for the redox peaks at around +225 mV. Whether the adsorption peaks were detectable or not was related to the thickness of membranes and the pre-retaining time before the formation of membranes.

IN-SITU SCANNING-TUNNELING-MICROSCOPY IMAGE OF A HIGHLY ORIENTED PYROLYTIC-GRAPHITE ELECTRODE MODIFIED WITH POTASSIUM BIS(11-MOLYBDOSILICATO) DYSPROSATE(III) IN SODIUM-SULFATE SOLUTION

The variation in molecule adsorption mode on pretreated highly oriented pyrolytic graphite electrodes, modified with the title complex K10H3[Dy(SiMo11O39)(2)] by cyclic voltammetry in the title complex solution, was observed in situ by electrochemical scanning tunnelling microscopy (ECSTM) with molecular resolution in sodium sulphate solution. According to the ECSTM images and the known molecular structure we conclude that the adsorption mode of the title complex modified electrode changed during potential cycling from ''vertical'' to ''inclined'' and then ''horizontal'' or ''flat'' mode, i.e. the title complex adsorbed on the surface of electrode by one ligand of the complex at first, then began to incline and was finally adsorbed by two ligands of the complex. This result indicates that the adsorption mode on the modified electrode surface changed during potential cycling in the sulphate solution and a much more stable molecular layer was formed. The change in adlattice of adsorbates on the modified electrode surface from hexagonal to rectangular was also observed by ECSTM. A plausible model was given to explain this process.

AN ORGANIC-PHASE ENZYME ELECTRODE BASED ON AN APPARENT DIRECT ELECTRON-TRANSFER BETWEEN A GRAPHITE ELECTRODE AND IMMOBILIZED HORSERADISH-PEROXIDASE

A mediatorless horseradish peroxidase (HRP) enzyme electrode operated in nonaqueous media is constructed by cryohydrogel immobilization.

Formation, Thermal Stability and Deformation Behavior of Graphite-Flakes Reinforced Cu-based Bulk Metallic Glass Matrix Composites

Graphite-flake reinforced Cu47Ti34Zr11 Ni-8 bulk metallic glass matrix composite was fabricated by water-cooled copper mould cast. Most of the graphite flakes still keep unreacted and distribute uniformly in the amorphous matrix except that some reactive wetting occurs by the formation of TiC particles around the flakes. It reveals that the presence of graphite flakes does not affect the onset of the glass transition temperature, crystallization reaction and liquidus of the metallic glass. The resulting material shows obvious serrated flow and higher fracture strength under room temperature compressive load, comparing with the monolithic bulk metallic glass (BMG). Three types of interaction between the shear bands and graphite flakes, namely, shear band termination, shear bands branching and new shear bands formation near the graphite flakes can be observed by quasi-static uniaxial compression test and bonded interface technique through Vickers indentation.

Analyses of the mechanical properties and microstructure of bamboo epoxy composites

Bamboo reinforced epoxy possesses reasonably good properties to waarrant its use as a structural material, and is fabricated by utilizing bamboo, an abundant material resource, in the technology of fibre composites. Literature on bamboo-plastics composites is rare. This work is an experimental study of unidirectional bamboo-epoxy laminates of varying laminae number, in which tensile, compressive, flexural and interlaminar shear properties are evaluated. Further, the disposition of bamboo fibre, the parenchymatous tissue, and the resin matrix under different loading conditions are examined. Our results show that the specific strength and specific modulus of bamboo-epoxy laminates are adequate, the former being 3 to 4 times that of mild steel. Its mechanical properties are generally comparable to those of ordinary glass-fibre composites. The fracture behaviour of bamboo-epoxy under different loading conditions were observed using both acoustic emission techniques and scanning electron microscopy. The fracture mode varied with load, the fracture mechanism being similar to glass and carbon reinforced composites. Microstructural analyses revealed that natural bamboo is eligibly a fibre composite in itself; its inclusion in a plastic matrix will help solve the problems of cracking due to desiccation and bioerosion caused by insect pests. Furthermore, the thickness and shape of the composite can be tailored during fabrication to meet specific requirements, thereby enabling a wide spectrum of applications.

One-Step Ionic Liquid-Assisted Electrochemical Synthesis of Ionic Liquid-Functionalized Graphene Sheet Directly from Graphite

Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at only 4.19 vol %, this composite has a conductivity of 13.84 S m(-1), which is 3-15 times that of polystyrene composites filled with single-walled carbon nanotubes.