Direct electrochemistry of bilirubin oxidase on three-dimensional gold nanoparticle electrodes and its application in a biofuel cell

We examined the direct electron transfer (DET) reaction of bilirubin oxidase (BOD) at three-dimensional gold nanoparticle (AuNP) electrodes in DET-type biofuel cells. The BOD-modified AuNP electrode, which does not have a thiol self-assembled monolayer, provided a current density as high as 5.2 mA cm−2 at a 4 000 rpm electrode rotation rate. A remarkable improvement in the stability of catalytic currents was also achieved by utilizing AuNP electrodes. Current densities retained about 90% of their initial value after 48 h of continuous measurement. Moreover, we constructed a mediator-free and compartmentless fructose/O2 biofuel cell based on DET-type bioelectrocatalysis via the BOD-cathode and the fructose dehydrogenase (FDH)-anode at pH 6.0. When carbon paper was used as the substrate upon which the electrode of the biofuel cell was constructed, the maximum current density of 2.6 mA cm−2 and the maximum power density of 0.66 mW cm−2 were achieved at 360 mV of the cell voltage in quiescent solution. Under stirring, a maximum current density of 4.9 mA cm−2 and a maximum power density of 0.87 mW cm−2 at an operating voltage of 300 mV were achieved.