We have studied the coimmobilization of glucose dehydrogenase (GDH) and its cofactor, oxidized nicotinamide adenine dinucleotide (NAD+), on a ketjenblack (KB) electrode as a step toward a biofuel cell anode that works without mediators. A KB electrode was first treated with a sulfuric acid/nitric acid/water mixture to lower the overvoltage for NADH oxidation, and was next chemically modified with NAD+ and GDH. The improved GDH/NAD+/KB electrode is found to oxidize glucose around 0 V vs. Ag/AgCl. A biofuel cell constructed with a bilirubin oxidase-immobilized KB cathode showed a maximum power density of 52 μW/cm2 at 0.3 V.
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