A composite poly azure B–clay–enzyme sensor for the mediated electrochemical determination of phenols

The biosensor construction is based on the entrapment of polyphenol oxidase (PPO) within a laponite clay film coated on an underlying poly azure B film (PAB) modified electrode. The amperometric detection consists in the electrochemical reduction of o-quinone, the product of the PPO reaction. Upon oxidative electropolymerization of azure B in aqueous electrolyte, an electroactive PAB is formed on the electrode surface. This underlying poly azure B film acts as a highly efficient electron shuttle between the cathode and the enzymatically generated o-quinone. The resulting composite PAB/PPO–laponite biosensor enabled the direct determination of 4 nM (<0.4 μg l−1) phenol, 0.4 nM (0.05 μg l−1) p-cresol and 0.2 nM (0.02 μg l−1) m-cresol in batch mode. Linearity of response over four orders of magnitude was achieved.