MEDIATED REAGENTLESS ENZYME-INHIBITION ELECTRODES

We have investigated the use of the copper-containing oxygenase enzyme s, laccase, tyrosinase and ceruloplasmin as reagentless enzyme activit y sensors. The system is based on the mediated reduction of oxygen by the enzymes co-immobilized in an osmium redox polymer hydrogel on glas sy carbon electrode surfaces. Both laccase and tyrosinase present rapi d homogeneous second-order rate constants for the interaction with a m odel monomer, [Os(2,2'-bipyridine)(2)(N-methylimidazole)Cl](+) (OsMeIm ). Ceruloplasmin rates are several orders of magnitude slower and no c atalytic currents are observed upon co-immobilization of this enzyme i n the redox hydrogel. The activity of the immobilized laccase and tyro sinase sensors is shown to be influenced by the enzyme loading in the deposition solution, the electrolyte pH and ionic strength. The immobi lized sensors can be utilized for the detection of modulators of enzym e activity, such as the respiratory poison azide. Reproducible inhibit ion curves can be obtained by normalization of the sensor response. Th e resulting enzyme inhibition biosensors can detect levels of azide as low as 1 mu M in solution and may be useful as an early warning senso r fro the presence of such respiratory toxins. (C) 1998 Elsevier Scien ce S.A. All rights reserved.