Mushroom tyrosinase-modified carbon paste electrode as an amperometric biosensor for phenols

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Abstract
A biosensor for a variety of substances could be readily prepared by the adsorption of partially purified mushroom tyrosinase at a carbon paste electrode, producing an enzyme layer which was protected with a dialysis membrane. The electrode poised at – 100mV (vs an Ag/AgCl reference electrode) functions on the basis of a reversible electrochemical reduction of the o-quinones formed from phenols in the tyrosinase reaction. The response times were 40 s for o-diphenols and 2 min for monophenols; the reproducibility for 10 consecutive assays of 3 μmol l-1 phenol solution was better than 4%. The detection limit was 10 nmol l-1 (catechol as substrate) and the steady state responses were linear up to a concentration of 200 μmol l-1. The optimum pH values were 6.0 for phenol and 6.5 for catechol. The shapes of the pH-response curves indicated the presence of at least two tyrosinase isoenzymes with different pH optima.

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