Fully Enzymatic Membraneless Glucose|Oxygen Fuel Cell That Provides 0.275 mA cm^-2 in 5 mM Glucose, Operates in Human Physiological Solutions, and Powers Transmission of Sensing Data

Coimmobilization of pyranose dehydrogenase as an enzyme catalyst, osmium redox polymers [Os(4,4′-dimethoxy-2,2′-bipyridine)₂(poly(vinylimidazole))₁₀Cl]⁺ or [Os(4,4′-dimethyl-2,2′-bipyridine)₂(poly(vinylimidazole))₁₀Cl]⁺ as mediators, and carbon nanotube conductive scaffolds in films on graphite electrodes provides enzyme electrodes for glucose oxidation. The recombinant enzyme and a deglycosylated form, both expressed in Pichia pastoris, are investigated and compared as biocatalysts for glucose oxidation using flow injection amperometry and voltammetry. In the presence of 5 mM glucose in phosphate-buffered saline (PBS) (50 mM phosphate buffer solution, pH 7.4, with 150 mM NaCl), higher glucose oxidation current densities, 0.41 mA cm^-2, are obtained from enzyme electrodes containing the deglycosylated form of the enzyme. The optimized glucose-oxidizing anode, prepared using deglycosylated enzyme coimmobilized with [Os(4,4′-dimethyl-2,2′-bipyridine)₂(poly(vinylimidazole))₁₀Cl]⁺ and carbon nanotubes, was coupled with an oxygen-reducing bilirubin oxidase on gold nanoparticle dispersed on gold electrode as a biocathode to provide a membraneless fully enzymatic fuel cell. A maximum power density of 275 μW cm^-2 is obtained in 5 mM glucose in PBS, the highest to date under these conditions, providing sufficient power to enable wireless transmission of a signal to a data logger. When tested in whole human blood and unstimulated human saliva maximum power densities of 73 and 6 μW cm^-2 are obtained for the same fuel cell configuration, respectively.