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Abstract:The relevance of polyphenols in human health is a well known fact. Prompted by that, very intensive research has been directed to get a method to detect them, which will improve the current ones. Laccase (p-diphenol:dioxygen oxidoreductase, EC 1.10.3.2) is a multi-copper oxidase, which couples catalytic oxidation of phenolic substrates with four electron reduction of dioxygen to water [1] . A maximum catalytic response in oxygenated electrolyte was observed between 4.5 and 5.5 [2], while for pH > 6.9 the laccase was found to be inactive [3]. We prepared a biosensor with laccase immobilised on a polyether sulphone membrane, at pH 4.5, which was applied at Universal Sensors base electrode. Reduction of the product of oxidation of several polyphenols, catalysed by laccase, was done at a potential for which the polyphenol of interest was found to respond. Reduction of catechol was found to occur at a potential of -200mV, which is often referred to in the literature for polyphenolic biosensors. However other polyphenols did not respond at that potential. It was observed that (+)-catechin produced a very large cathodic current when +100mV were applied to the laccase biosensor, both in aqueous acetate and 12% ethanol acetate buffer , whereas caffeic acid responded at -50mV. Other polyphenols tested were gallic acid, malvidin, quercetin, rutin, trans-resveratrol.

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