Azine/hydrogel/nanotube composite-modified electrodes for NADH catalysis and enzyme immobilization

The development of new, efficient bioelectrodes is important to the improvement of biosensor and biofuel cell technology. NAD-dependent dehydrogenase enzymes represent a diverse field of oxidoreductase enzymes that can be used to create unique biosensors and biofuel cells, but require electrocatalysts to oxidize NADH in order to harvest the electrons efficiently from fuel oxidation. This study presents a new methodology for the co-immobilization of dehydrogenase enzymes, azine-based NADH electrocatalysts, carbon nanotubes, and polymer hydrogels. The easy “one-pot” mixing and casting procedure is shown to produce electrodes that can electro-oxidize NADH at low potentials. In situ electropolymerization of the azine dyes within the composites is shown to improve NADH sensitivity, but harms enzyme activity. Biosensors and biofuel cells are constructed with a model enzyme, glucose dehydrogenase, to show the application of this system in a glucose biosensor and biofuel cell. Glucose biosensors produced limiting current densities of 400 μA/cm2 and glucose/air-breathing biofuel cells produced power densities slightly greater than 100 μW/cm2.