MUSHROOM TYROSINASE-MODIFIED CARBON PASTE ELECTRODE AS AN AMPEROMETRIC BIOSENSOR FOR PHENOLS

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 - 100 mV (vs an Ag/AgC1 reference electrode) functions on the basis of a reversible electrochemical reduction of the omicron-quinones formed from phenols in the tyrosinase reaction. The response times were 40 s for omicron-diphenols and 2 min for monophenols; the reproducibility for 10 consecutive assays of 3-mu-mol l-1 phenol solutions was better than 4%. The detection limit was 10 nmol l-1 (catechol as substrate) and the steady state repsonses were linear up to a concentration of 200-mu-mol 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.