Indium oxide electrodes gold-doped

Use of modified gold electrodes is not the only approach to achieve cytochrome c electrochemistry. Indeed, a number of studies have been reported on a variety of electrode surfaces. In 1977, Yeh and Kuwana illustrated (23) well-behaved voltammetric response of cytochrome c at a tin-doped indium oxide electrode the electrode reaction was found to be diffusion-controlled up to a scan rate of 500 mV sec Metal oxide electrodes were further studied (24, 25) independently in Hawkridge and Hill s groups. The electrochemical response of cytochrome c at tin-doped indium oxide and fluoride-doped tin oxide was very sensitive to the pretreatment procedures of the electrode surface. At thin-film ruthenium dioxide electrodes, variation of the faradaic current with pH correlating with the acid-base protonation of the electrode surface was observed. 

A.2.2 Solid electrodes (gold, carbon, metal oxide electrodes). Cytochrome c is also adsorbed irreversibly at solid electrodes, which mostly results in irreversible kinetices of the electrode reaction. A nearly reversible reaction of strongly adsorbed cytochrome c is, however, observed at electrodes of metal oxides (doped metal oxide semiconductor electrodes, tin-doped indium oxide electrode) [202, 203]. 

The first reports on direct electrochemistry of a redox active protein were published in 1977 by Hill [49] and Kuwana [50], They independently reported that cytochrome c (cyt c) exhibited virtually reversible electrochemistry on gold and tin doped indium oxide (ITO) electrodes as revealed by cyclic voltammetry, respectively. Unlike using specific promoters to realize direct electrochemistry of protein in the earlier studies, recently a novel approach that only employed specific modifications of the electrode surface without promoters was developed. From then on, achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters had made great accomplishments. 

The first reports on a reversible DET between redox proteins and electrodes were published in 1977 showing that cytochrome c is reversibly oxidized and reduced at tin-doped indium oxide [30] and gold in the presence of 4,4 -bipyridyl [31]. Only shortly after these publications appeared, papers were published describing the DET between electrode and enzyme for laccase and peroxidase [32,33]. It was observed that the overpotential for oxygen reduction at a carbon electrode was reduced by several hundred millivolts compared to the uncatalyzed reduction when laccase was adsorbed. This reaction could be inhibited by azide. The term bioelectrocatalysis was introduced for such an acceleration of the electrode process by... 

For electropolymerization an anode made of glassy carbon (CWE), gold (Au), platinum disk or plate (Pt), or tin-doped indium-oxide-coated glass (ITO) are commonly used as working electrodes. A platinum wire or mesh is used as the counterelectrode. The potential is measured vs silver/silver chloride (Ag/AgCl) or saturated calomel (SCE) electrodes. Alternatively, a silver wire can be used as a pseudoreference with calibration to the half-wave potential of the ferrocene/ferrocenium (Fc/Fc ) redox couple. 

A thin-layer cell is fabricated based on two optically transparent windows. The thickness of the electrolyte layer is dictated by the thickness of the optically transparent working electrode, usually a gold minigrid, indium-doped tin-oxide-coated glass slide or a reticulated vitreous carbon slice. This approach is not surface-sensitive, and it is effectively restricted to nonaqueous solvents, because the minimum electrolyte thicknesses that can be achieved cause severe attenuation in the IR beam. 

With optically transparent electrodes (OTE), molecular adsorbates, polymer films, or other modifying layers attached to the electrode surface or being present in the phase adjacent to the electrode can be studied. With opaque electrode materials, internal or external reflection may be applied. Glass, quartz, or plastic substrates coated with a thin layer of semiconductors (indium-doped tin oxide) or conducting metals (gold, platinum) are often used as OTE. The optically transparent electrode is immersed as working electrode in a standard cuvette. 

In order to decrease the overpotential for cysteine oxidation in cysteine-containing peptides, graphite-epoxy resin or carbon paste electrodes with immobilized cobalt phthalocyanine have been employed in HPLC systems [53,87-89]. Glassy carbon electrodes modified with a mixed-valence ruthenium(I V,III) oxide film stabilized by cyano cross-links [61,62], indium ferricyanide [63], or a Prussian blue film [64], and a bismuth(V)-doped lead dioxide Pb02 film on gold [65] have also been used for detection following HPLC separation. In addition, a carbon fiber modified with a nfixed-valence ruthenium(IV,III) oxide film stabilized by cyano cross-links has been used in CE [46]. 

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