A regenerable pseudo-reagentless glucose biosensor based on Nafion polymer and l,1'-dimethylferricinium mediator

Glucose oxidase was immobilized onto electrodes by co-deposition from an aqueous solution containing the diluted ion-exchange polymer Nafion. The cationic exchange property of the polymer was used to provide high local concentrations of l,1'-dimethylferricinium (DMFc⁺) mediator in the film by exchange from solution. The mediated electrodes were operated at +200 mV (vs. ), and the Nafion film was shown to reduce interfering current from ascorbate anion. Cyclic voltammetric analysis revealed a fourteen-fold increase in the effective DMFc⁺ activity at the electrode after extraction into the film. The sensitivity to glucose was 52 μA/cm²/mM in a solution containing 0.09 mM DMFc⁺, which is at least three-fold greater than reported for similar electrodes using hydrogen peroxide detection at +650 mV, with a response time of less than 1 min for a 10 μm thick membrane. Oxygen interference was significant, requiring deaeration of the solution before analysis. The electrodes exhibited no significant decrease in sensitivity for more than 50 days on storage in acetate buffer. Electrodes covered with 8000 MWCO dialysis membrane slowed the exchange of DMFc⁺ with the solution such that the Nafion film functioned as a mediator reservoir. This permitted reagentless analysis of glucose, typically capable of twenty assays when measuring concentrations between 0.1 and 1 mM. The sensitivity for glucose was 7.85 μA/cm²/mM, which is 15% of the sensitivity for the electrode without the dialysis membrane. The detection limit was 20 μM, with a linear range extending to about 3 mM, giving a dynamic range of over two orders of magnitude. Thus where some sacrifice of sensitivity and response rate may be made, the dialysis membrane cover enables multiple analyses in a reagentless biosensor scheme.