The oxidation of dopamine has been studied particularly for in vivo application where signaling mechanisms between cells are investigated. The reduction of anthraquinones is important as redox mediators 21 and in particular in the catalytic reduction of oxygen to hydrogen peroxide. Both of these systems have been studied for a considerable time. The redox systems selected for this study are the two-electron reduction of anthraquinone and the two-electron oxidation of dopamine 20 to reect possible problems of interference during reduction (oxygen) and interference during oxidation (ascorbate). In fact, the interfering species can be essentially removed from the inter-electrode or "trench" region with potential future applications in nanoscale in situ separation and detection. As a result, the collector limiting current reading becomes insensitive to the interfering species. ![]() With two active electrodes, the generator and the collector, one electrode can be polarized to actively remove chemically irreversible redox systems, such as O 2 or ascorbate, from the "trench" region of the dual-plate electrode system. In this report it is demonstrated that ITO-ITO dual-plate electrode systems assembled by placing a thin layer of epoxy between two ITO electrodes (see ) can be employed in electroanalytical tasks where interference from oxygen or other chemically irreversible redox active reagents traditionally causes problems. Here, further benets of this type of electrode system where separated trench "interior" and "mouth" regions can be assigned (see red and green regions in, respectively) are identied in terms of suppression of interference responses and effects. A particularly useful sensor geometry is the dual-plate or "trench" electrode system which was initially developed, reported, and treated by Anson, Reilley, and Hubbard, and more recently employed in electroanalysis. More generally, the generator-collector conguration with bipotentiostatic control offers benets due to (i) the steady state nature of analytical responses, (ii) the amplication effect, which is inversely proportional to the inter-electrode gap d (in rst approximation ) I feedback ¼ nDFAc d with n, the number of electrons transferred per molecule diffusing into the electrode, D the diffusion coefficient, F the Faraday constant, A the area, and c the concentration, and (iii) the possibility to ll the trench with a "lter" or "separation" material such as cellulose. In the extreme limit, as dual-plate nano-gap sensors, these kinds of electrode systems can be employed down to single molecule sensitivity and with the opportunity for novel statistical analysis techniques being developed. ![]() Recently, the benets of "junction electrode systems" 4 with generator-collector or modulator-sensor 7 electrode arrangements under bipotentiostatic control have been highlighted. Sensitivity and selectivity of electrodes as well as multi-purpose analysis applications are of interest. Electrochemical methods are attractive as they oen allow rapid on-site or pointof-care measurements without the need for separation or offline laboratory apparatus. New types of electrochemical sensor electrodes are desirable, in particular for applications in complex media and multi-analyte cases, 1 for example, in blood analysis. ![]() This spatial separation of chemically reversible and irreversible processes within and outside the trench is discussed as a potential in situ microscale sensing and separation tool. Finally, dopamine oxidation in the presence of ascorbate is demonstrated with the irreversible oxidation of ascorbate at the "mouth" of the trench electrode and chemically reversible oxidation of dopamine in the trench "interior". For the oxidation of dopamine on ITO, novel "Piranha-activation" effects are observed and chemically reversible generator-collector feedback conditions are achieved at pH 7, by selecting a more negative collector potential, again eliminating possible oxygen interference. The reversible 2-electron anthraquinone-2-sulfonate redox system is demonstrated to give well-defined collector responses even in the presence of oxygen due to the irreversible nature of the oxygen reduction. A generator-collector trench electrode system prepared from two tin-doped indium oxide (ITO) electrodes placed vis-à-vis with a 22 mm inter-electrode gap is employed here as a sensor in aqueous media. Generator-collector electrode systems are based on two independent working electrodes with overlapping diffusion fields where chemically reversible redox processes (oxidation and reduction) are coupled to give amplified current signals.
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