Electrochemical glucose sensor based on a phenothiazine derivative mediator with nicotinamide adenine dinucleotide-dependent glucose dehydrogenase

The phenothiazine derivative (M2) was utilized as a redox mediator for the redox processes of the nicotinamide adenine dinucleotide (NAD⁺) cofactor. The composite solutions were prepared by mixing NAD⁺-dependent glucose dehydrogenase with NAD⁺, M2, poly-l-lysine, and glutaraldehyde. Glucose sensors were fabricated by casting various composite solutions onto the reduced graphene oxide-modified gold electrode and additional Nafion coating processes. The composition of electrode materials (ratio and amount of each component) and measurement conditions (applied potential, pH, and temperature) were optimized to obtain the highest sensitivity. The sensor showed a low reference effect, high selectivity toward interfering species, and long-term stability. The glucose sensor performed well when human serum was injected as the actual sample and compared with a standard solution. These findings promote the development of electrochemical sensors based on other NAD⁺-dependent enzymes.