THEORETICAL TREATMENT OF DIFFUSION AND KINETICS IN AMPEROMETRIC IMMOBILIZED ENZYME ELECTRODES .1. REDOX MEDIATOR ENTRAPPED WITHIN THE FILM

A comprehensive treatment of the diffusion and reaction within a uniform film containing immobilized enzyme and mediator at an electrode surface is presented. Approximate analytical solutions and the results of numerical simulations using the relaxation method with automatic grid point allocation are compared and found to be in excellent agreement. Case diagrams are presented showing the interrelation between the different limiting cases. Analytical expressions for the current in each limiting case are given, the behaviour of the system is discussed, and the rate-limiting processes are identified. The potential dependence of the current is shown to be a useful diagnostic together with variation in film thickness, enzyme loading, mediator loading and substrate concentration. The model is appropriate to the study of systems such as glucose oxidase entrapped within a redox hydrogel film or immobilized within a polyelectrolyte membrane containing an electrostatically entrapped mediator.