Design of Experiments Approach to Provide Enhanced Glucose-oxidising Enzyme Electrode for Membrane-less Enzymatic Fuel Cells Operating in Human Physiological Fluids

Graphite electrodes are modified with a redox polymer, [Os(4,4′-dimethoxy-2,2′-bipyridine)₂(polyvinylimidazole)₁₀Cl]⁺ (E°′=−0.02 V vs Ag/AgCl (3 M KCl), crosslinked with a flavin adenine dinucleotide glucose dehydrogenase and multi-walled carbon nanotubes for electrocatalytic oxidation of glucose. The enzyme electrodes provide 52 % higher current density, 1.22±0.10 mA cm⁻² in 50 mM phosphate-buffered saline at 37 °C containing 5 mM glucose, when component amounts are optimised using a design of experiments approach compared to one-factor-at-a-time. Current densities of 0.84±0.15 mA cm⁻² were achieved in the presence of oxygen for these enzyme electrodes. Further analysis of the model allowed for altering of the electrode components while maintaining similar current densities, 0.78±0.11 mA cm⁻² with 34 % less enzyme. Application of the cost-effective anodes in membrane-less enzymatic fuel cells is demonstrated by connection to cathodes prepared by co-immobilisation of [Os(2,2′-bipyridine)₂(polyvinylimidazole)₁₀Cl⁺] redox polymer, Myrothecium verrucaria bilirubin oxidase and multi-walled carbon nanotubes on graphite electrodes. Power densities of up to 285 μW cm⁻², 146 μW cm⁻² and 60 μW cm⁻² are achieved in pseudo-physiological buffer, artificial plasma and human plasma respectively, showing promise for in vivo or ex vivo power generation under these conditions.