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Interdigitated array microelectrodes for the determination of enzymatic activities


Federation of European Chemical Societies, London; Royal Society of Chemistry -RSC-, London:
EUROANALYSIS-8. 8. European Conference on Analytical Chemistry '93. Proceedings
European Conference on Analystical Chemistry <8, 1993, Edinburgh>
Conference Paper
Fraunhofer ISIT ()

Microelectrode arrays are receiving particular attention. One very attractive feature is the possibility of electrochemical signal amplification by redox recyclisation of reversible electron mediators. For this purpose platinum microband electrodes have been fabricated in an interdigitated array with an interelectrode space of 2 Mym. At this distance each electrode (when polarised) is within the diffusion layer of the other electrode. Therefore oxidised and reduced forms of reversible redox couples can be repeatedly converted back and forward, when the respective potentials are applied at the electrode pairs. As a result the anodic and cathodic currents are increased. This principle of electrocatalytic signal amplification has been applied to the determination of alkaline phosphatase activity. The chosen enzyme substrate was p-aminophenol phosphate, which exhibits an irreversible oxidation peak in cyclic voltammetry at about +450 mV versus Ag/AgCl. Whereas the product of the enzymatic hydrolysis p-aminophenol is reversibly oxidised at potentials around +150 mV without interference from the parent phosphate ester. Amplification of the monitored anodic current is obtained when the second microband electrode of the interdigitated array is used as cathode, where p-aminophenol is immediately regenerated, thus entiring the next redox conversion cycle. The determination of alkaline phosphatase activity with the proposed redox recycling system is applicable to immunoassays, where alkaline phosphatase is used as enzyme label.