LEACHING OF DIMETHYLFERROCENE, A REDOX MEDIATOR IN AMPEROMETRIC ENZYME ELECTRODES

Glucose electrodes were prepared by electrochemical oxidation of graphite and covalent binding of glucose oxidase to the functionalized surface; some of the electrodes were additionally modified by adsorption of the artificial electron acceptor 1,1′-dimethylferrocene. The long-term responses of two kinds of electrodes were compared in a flow-injection system. While the unmodified electrode (current generation by H2O2 oxidation at 600 mV versus SCE) remained stable for more than 3 days, the dimethylferrocene-mediated system (100 mV versus SCE) rapidly lost its activity. However, response could in part be restored by adsorption of new mediator. The loss of 1,1′-dimethyl-ferrocene from graphite electrodes could be shown by cyclovoltammetry and steady-state current-voltage curves. In rotating ring-disk electrode experiments, current generation at the concentric platinum electrode could only be observed when the central graphite disk electrode, modified with 1,1′-dimethylferrocene, was poised to a potential higher than the oxidation potential of ferrocene. Consequently, the 1,1′-dimethylfericinium cation must be the leaching agent. The results are discussed with respect to electrode stability and intoxication problems arising in the case of in vivo application. © 1990.