Mediated enzyme reactions form the basis of many applications, ranging from biosensors, through biocatalytic fuel cells, to applications in industrial electrolysis. This presentation will review some of our efforts to date on redox mediation of enzyme reactions for such applications. Our initial research in this area focused on mediated reactions of laccases, a class of copper-based oxidase enzymes that catalyze the four-electron reduction of oxygen to water. Immobilization of the enzyme in a redox mediating hydrogel yields reagentless biosensors, as monitoring of mediated reduction currents for oxygen, present in solution, permits detection of any modulator of enzyme activity. Furthermore, co-immobilization of a redox mediator and an affinity recognition element, such as DNA or antibody, provides a generic platform for the amplified detection of complementary affinity partners (DNA or antigen) that are labelled with redox enzymes. Our studies on laccase biosensors demonstrated, also, that laccases co-immobilized in redox hydrogels can reduce oxygen at relatively high potentials and current densities, suggesting possible applications as cathodes in implantable biofuel cells when combined to oxidation of a fuel, such as glucose, at the anode.
Covalent coupling of enzymes and mediators on the electrode surface can appreciably improve the fuel cell stability. Also, improvements in the design of the redox complexes and polymers (in terms of structure and redox potential) help to increase biosensor and biofuel cell performance. Our approach to improving the stability and the performance of thse devices through tailored surface modification will be presented.