Indium oxide/gold electrodes

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. 

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

For spectroelectrochemical and photoelectrochemical studies, optically semi-transparent electrodes have been fabricated by vapour deposition techniques on glass or quartz substrates (Chapter 12). Tin and indium oxides, platinum, and gold have been used. 

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... 

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. 

Similarly, Kawai et al. [30] use the concept of changes in electrical conductivity associated with a photochromic response. This polymer (see Fig. 6.8) was found to be soluble in common organic solvents. UV irradiation of a thin film of the polymer turned the film blue. For the measurement of photoinduced conductivity changes, an approximately lOOnm thick polymer film was deposited on an indium tin oxide electrode. A gold electrode about 20 nm thick was then evaporated on top of the polymer film. Before the gold deposition, the polymer film was irradiated with UV... 

It has been reported that a reversible one-electron transformation of cytochrome c occurs on an indium oxide electrode. Cytochrome c yields quasi-reversible maxima at EhO 0. 25 V on a gold electrode in the presence of 4,4 -bipyridine. 

Deepshikha etal. have fabricated a novel nanobiocomposite bienzymatic amperometric cholesterol biosensor, coupled with cholesterol oxidase (ChOx) and horseradish peroxidase (HRP), based on the gold nanoparticle-decorated graphene-nanostructured PANI nanocomposite (NSPANI-AuNP-GR) film which was electrochemically deposited onto indium tin oxide (ITO) electrode from the nanocomposite (NSPANI-AuNP-GR) dispersion, as synthesized by in situ polymerization technique [166]. The... 

Substrates, Films are usually prepared on platinum or gold electrodes which are inert, but semiconducting materials including indium tin oxide, n-type polycrystalline silicon, gallium arsenide, cadmium sulphide and cadmium selenide, graphite [38, 59], and oxide covered metals [60] have also been used. In the majority of cases, the films are produced readily and the only serious limitations are the potential and the nucleophilic nature of the solution. 

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. 

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