Advances in amperometric enzyme electrodes in reversed micelles

Some new trends in the development of amperometric enzyme electrodes in reversed micelle systems are shown. The possibility of using these media for on-line applications as well as for enzyme inhibition measurements both in the batch and the flow-injection modes is demonstrated. Reversed micelles were formed of ethyl acetate as organic solvent, dioctyl sulfosuccinate as emulsifying agent and a 4% of 0.05 mol l−1 phosphate buffer of pH 7.4 as aqueous phase. An Eastman AQ/enzyme immobilization approach was used. Flow-injection analysis of various phenolic compounds using the reversed micelle as the carrier solution was accomplished. Despite the hydrodynamic conditions, the immobilized enzyme layer displayed a good stability in the reversed micelle flowing stream. Phenolic compounds with all ortho-positions substituted gave no analytical signal. The possibility of developing reversed micelle enzyme inhibition biosensors is illustrated by monitoring inhibitors of tyrosinase such as benzoic acid, thiourea or propyl gallate, and using phenol as the substrate. The steady-state response towards phenol rapidly decreases upon additions of these compounds at a low concentration level. A reversible inhibition process was shown in all cases, and the type of enzyme inactivation in the reversed micelle of each inhibitor studied. The rapid response of the tyrosinase electrode to the changes of inhibitor concentration in the reversed micelle can be also exploited for on-line applications.