Characterization of Mixed Enzyme-Mediator-Carbon Paste Electrodes

Amperometric bioelectrodes based on carbon paste mixed with glucose oxidase (GOX) and dimethylferrocene (DMFc), are characterized by using cyclic voltammetry, potential step chronoamperometry and amperometry at a rotating disk electrode. The catalytic process appears to be highly dependent on the amount of DMFc. Kinetic control, internal diffusion control and external diffusion control can be obtained only by varying the amount of incorporated DMFc. It was shown that the Eadie-Hofstee plot is a particularly useful tool in diagnosis of diffusional limitations. The high efficiency of electrochemical regeneration of high amounts of DMFc∗ surrounding GOX solves the problem of co-substrate transport. The catalytic oxidation current of ascorbic acid was highly diminished by casting a lipid/Nafion membrane and totally eliminated by treatment of the sample with hydrogen peroxide prior to measurement.