Tricatalytic Organocatalyst–Enzyme Hybrid Cascade for Improving Complete Oxidation of Glucose to Carbon Dioxide

Advancing energy harvesting is crucial for the development of wearable and implantable technologies. Given the high concentration of complex fuels, such as glucose, in biological fluids, biofuel cells present a promising avenue for exploration. However, glucose fuel cells that have been published to date typically catalyze only one or two of the maximum 12 oxidation steps for glucose, resulting in low energy density. Although known multienzyme cascades, which are sequential biochemical reactions where multiple enzymes work in tandem to convert a substrate into a final product, have addressed this inefficiency, they come with several trade-offs, such as reduced power density due to poor overlapping enzyme activity, increased resistance, and limited active site accessibility. By centralizing the roles of several enzymes into a single promiscuous catalyst, it may be possible to overcome many of the challenges faced by multienzyme cascades. Here, we developed a hybrid bioanode demonstrating complete glucose oxidation to carbon dioxide (CO2), using only a robust electro-organic catalyst, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO), and two suitable enzymes, 2-keto-3-deoxygluconate aldolase from Sulfolobus solfataricus (ssKDGA) and oxalate decarboxylase (OxDC) from Bacillus subtilis. Our electrochemical experiments support 4-amino-TEMPO-mediated oxidations, while LC/MS and NMR of bulk electrolysis products confirm the production of catalytic intermediates and CO2. After 12 h of bulk electrolysis, our hybrid system demonstrated a 2-fold increase in current density compared to previous multienzyme cascades.