Reagentless amperometric glucose dehydrogenase biosensor based on electrocatalytic oxidation of NADH by osmium phenanthrolinedione mediator

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Abstract
The mediator Os(4,4′-dimethyl, 2,2′-bipyridine)2(1,10-phenanthroline-5,6-dione) was used for the catalytic oxidation and recycling of NADH. The mediator, with a redox potential of almost 0 V versus Ag/AgCl, shows clear electrocatalysis of NADH at 0.1 V versus Ag/AgCl at pH 6.0. Carbon paste electrodes modified with the mediator show a clear electrocatalytic wave reaching limiting current densities at 0.15 V versus Ag/AgCl of the order of 140 µA cm–2 l mmol–1 NADH. Reagentless dehydrogenase carbon paste amperometric electrodes for glucose were developed, mixing the mediator, glucose dehydrogenase and NAD+ in the paste. These electrodes were optimized with respect to amounts of enzyme, mediator and NAD+ and were studied with a variety of electrochemical techniques. The results suggest that the response is limited by the enzymic step of the reduction of NAD+ or the oxidation of the substrate. The glucose electrodes show maximum current densities of >0.5 mA cm–2 and very good operational stability in continuous operation; under dry storage conditions their lifetime exceeded 1 month.

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