Separator-less Amino Acid-powered Biofuel Cell Through an Artificial Multi-enzyme Cascade Reaction

Objective This study was aimed at constructing a highly stable one-compartment enzymatic biofuel cell (EFC) without a separator through a multi-enzyme cascade reaction pathway. Results A separator-less EFC composed of a multi-enzyme cascade anode containing four dehydrogenases from a thermophile and a cathode devised using a multi-copper oxidase mutant with enhanced enzyme activity from a hyperthermophile was developed. To fabricate an EFC without a separator, redox mediators utilized in the enzymatic cascade reaction were also immobilized on the anode. In the presence of the fuel 100 mM L -proline, the separator-less EFC with four thermophilic dehydrogenase-modified anode achieved a maximum power density of 11.3 υW/cm 2 at 37°C, which was 1.6-fold higher than that of a similar EFC fabricated with a one enzyme-modified anode. The separator-less EFC composed of a multi-enzyme modified anode maintained approximately 57% of the load current at 0.3 V measured on the first day of EFC fabrication, even after 4 days.Conclusion Efficient L-proline electric generation utilizing a separator-less EFC composed of a multi-enzyme modified anode through a multi-step fuel oxidation reaction and a highly stable multi-copper oxidase mutant-modified cathode was successfully achieved over a long period. The long-term stability of the separator-less EFC can facilitate its application as an efficient power source for implantable medical devices requiring continuous operation.