Raman spectroelectrochemical study of electrochemical decomposition of poly(neutral red) at a gold electrode.

A gold electrode, modified with poly(neutral red), has been studied with surface-enhanced resonance Raman spectroscopy at 676.4 nm excitation. It has been shown that both qualitative and quantitative changes in Raman spectra occur during prolonged holding of the modified electrode in pH 7.0 solution at a controlled electrode potential ranging from -0.6 to -0.2V vs. Ag/AgCl, indicating that a decomposition of the poly(neutral red) layer proceeds. The decomposition proceeds slower at a more negative electrode potential. From kinetic data obtained, first-order decomposition rate constants have been calculated, ranging from 9.17x10(-4) to 1.09x10(-2) min(-1) for electrode potential ranging from -0.6 to -0.2 V.

Effect of yeast pretreatment on the characteristics of yeast-modified electrodes as mediated amperometric biosensors for lactic acid.

Carbon paste electrode modified with baker' and wine yeast Saccharomyces cerevisiae (a source of flavocytochrome b(2)) were investigated as amperometric biosensors for L-lactic acid. Before immobilization on the electrode surface, yeast cells were pretreated with various electrolytes, alcohols and weak organic acids. Electrode responses to L-lactic acid were tested in the presence of various mediators (potassium ferricyanide, phenazine methosulfate, 2,6-dichlorophenolindophenol sodium salt hydrate, 1,2-naphthoquinone-4-sulfonic acid sodium salt). The highest (144+/-7 nA per 0.2 mM L-lactic acid) and the most stable responses were obtained after yeast pretreatment with 30% ethanol using potassium ferricyanide as a mediator. Different electrode sensitivities with mediator phenazine methosulphate probably reflected diverse changes in yeast membrane (and/or cell wall).

Mediated amperometric biosensors for lactic acid based on carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae.

Carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae (a source of flavocytochrome b(2)) were investigated as amperometric biosensors for lactic acid. Phenazine methosulphate was used as a mediator. The optimal operational conditions of the electrodes were: an operating potential 0.0 V, solution pH 7.2, concentration of phenazine methosulphate in solution 0.2 mM. A linear range in the dependence of the current responses on the concentration of lactic acid was up to 1 mM. The suitability of the electrodes for determination of lactic acid in milk and dairy products such as kefir and yoghurt was tested. The yeast cells in the paste remained viable at least for 1 month.

Conducting polymer-based nanostructurized materials: electrochemical aspects.

New modern technologies require new materials. During the past decade, the movement towards nanodimensions in many areas of technology aroused a huge interest in nanostructurized materials. The present article reviews recent works dealing with electrochemistry-related aspects of nanostructurized conducting polymers. Electrochemical synthesis and some properties of nanostructurized conducting polymers, and nanocomposites derived from conducting polymers and metals, carbon, and inorganic and organic materials are considered. Some potential areas for electrochemistry-related applications of nanocomposites are highlighted, including batteries, supercapacitors, energy conversion systems, corrosion protection, and sensors.

Electrochemical response of ascorbic acid at conducting and electrogenerated polymer modified electrodes for electroanalytical applications: a review.

The present short review deals with electroanalytical aspects of electrochemical response of ascorbic acid (Vitamin C) at conducting and electrogenerated polymer modified electrodes. Two main topics are considered: (i) electrocatalytic oxidation of ascorbate at conducting polymer modified electrodes, leading to electroanalytical techniques for ascorbate assay, and (ii) retardation of ascorbate penetration through a layer of electrogenerated polymers, leading to permselective coatings and their diverse uses, especially for biosensing devices.

Investigation of electrochemical properties of FMN and FAD adsorbed on titanium electrode.

The electrochemical properties (such as the values of the formal potentials, the dependence of the formal potentials on solution pH, the reversibility of the electrochemical process) of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) adsorbed on a titanium electrode were dependent on the electrolyte. The formal potentials of adsorbed FMN and FAD in phosphate, HEPES and PIPES buffers at pH 7 were similar to those for dissolved flavins (-460 to -480 mV vs. SCE) and changed linearly with a slope of about 52 mV per pH unit in the pH region 3 to 8. In TRIS buffer, the formal potentials of adsorbed FMN and FAD were also pH-dependent, however, with invariance in the pH range 4.5 to 5.5. In non-buffered solutions (KCl, LiCl, NaCl, CsCl, CaCl(2), Na(2)SO(4) at different concentrations), the electrochemical behavior of adsorbed FMN and FAD differed from that of dissolved flavins and was dependent on the electrolyte (especially at pH 4.5 and pH 5). Under certain conditions (electrolyte, concentration, pH), a two-step oxidation of FMN could be observed.

Electropolymerization of Preadsorbed Layers of Some Azine Redox Dyes on Graphite.

The redox-active azine dyes Nile blue A (NB) and Toluidine blue O (TB) were electropolymerized after preadsorption onto the surface of graphite electrodes by potential cycling, using an anodic scan limit of 0.9 or 1.0 V vs SCE, where irreversible electrooxidation of the dye proceeds, yielding polymerizable species. Electropolymerization of both dyes is followed by the progressive disappearance of the characteristic current peaks in the cyclic voltammograms, and formation of new ones, shifted by ca. 0.21 V to the positive direction. Also, a decrease and gradual disappearance of the characteristic luminescence at a maximum of 671 nm was observed during the electropolymerization of NB. The resulting electrodes, modified by electropolymerized derivatives of NB and TB, were shown to be able to catalyze the electrooxidation of the coenzyme NADH. Thus, the modified electrodes prepared can be used for amperometric detection of the reduced form of the coenzyme. Copyright 2000 Academic Press.

Electrocatalytic Oxidation of Coenzyme NADH at Carbon Paste Electrodes, Modified with Zirconium Phosphate and Some Redox Mediators.

Carbon paste electrodes (CPE), modified with zirconium phosphate (ZrP) along with some redox mediators, were prepared and shown to be active in electrocatalytic oxidation of coenzyme NADH. Nile blue (NB), methylviologen (MV), and benzylviologen (BV) were added to ZrP-containing CPE, showing a shift of their redox potentials toward the positive direction, ranging from ca. 0.20 to 0.35 V. This shift was interpreted in terms of different complexation abilities of oxidized and reduced forms of mediators with the host matrix. The modified electrodes prepared showed electrocatalytic activity for electrooxidation of NADH. The i,c-dependencies for the modified electrodes were shown to follow Michaelis-Menten kinetics. For C:ZrP:NB and C:ZrP:MV electrodes, Michaelis constants of 0.870 +/- 0.012 and 0.153 +/- 0.015 mM, respectively, were obtained. The sensitivity of C:ZrP:NB and C:ZrP:MV electrodes to NADH varied from 19.2 to 60.8 and from 18.4 to 50.9 µA/mM c cm(2), respectively, by changing the working potential from -0.2 to 0.2 V vs. SCE. Copyright 2000 Academic Press.

Development of biosensors based on hexacyanoferrates.

Ferric and copper hexacyanoferrates (PB and CuHCF, respectively) were electrodeposited on glassy carbon electrodes providing a suitable catalytic surface for the amperometric detection of hydrogen peroxide. Additionally glucose oxidase was immobilized on top of these electrodes to form glucose biosensors. The biosensors were made by casting glucose oxidase-Nafion layers onto the surface of the modified electrodes. The operational stability of the films and the biosensors were evaluated by injecting a standard solution (5 muM H(2)O(2) for PB, 5 mM H(2)O(2) for CuHCF and 2.5 mM glucose for both) over 5-10 h in a flow-injection system with the electrodes polarized at -50 (PB) and -200 mV (CuHCF) versus Ag/AgCl, respectively. The glucose biosensors demonstrated suitability for glucose determination: 0.0-2.5 mM (R(2)=0.9977) for PB and 0.0-10 mM (R(2)=0.9927) for CuHCF, respectively. The visualization of the redox catalyst modifiers (PB and CuHCF films) was presented by scanning electron micrographs.

Amperometric glucose biosensors based on Prussian Blue- and polyaniline-glucose oxidase modified electrodes.

The properties of glucose sensors fabricated by immobilization of glucose oxidase in a layer of electrochemically deposited polyaniline were investigated. Selective amperometric glucose sensors were prepared by immobilization of glucose oxidase on a Prussian Blue-modified platinum electrode in a layer of polyaniline during a one-step electropolymerization procedure from phosphate buffer. The influence of ascorbic acid and acetaminophen was completely eliminated due to impermeability of polyaniline to these substances.

Tuning the redox potential of riboflavin by zirconium phosphate in carbon paste electrodes.

Modified carbon paste electrodes were prepared by inclusion of riboflavin together with zirconium phosphate (ZrP) into carbon paste. The midpoint potential for riboflavin in this electrode was found to be -0.259 V vs. SCE and shifted by 0.207 V to the positive direction, as compared to carbon paste electrode not containing ZrP. The electrode prepared was shown to electrocatalyse the anodic oxidation of the coenzyme NADH in the potential range of 0.0 to 0.25 V.