Oxygen reduction reactions of the thermostable bilirubin oxidase from Bacillus pumilus on mesoporous carbon-cryogel electrodes

This study demonstrates the bioelectrocatalytic reactions of a new bilirubin oxidase (BOD) from Bacillus pumilus on a mesoporous carbon cryogel (CCG) electrode, in the presence and absence of a mediator. BOD, physically adsorbed on the mesoporous matrix of a CCG electrode, allowed a direct electron transfer (DET) from the carbon electrode to the type I copper site of the enzyme. The current from the dioxygen reduction reaction (ORR), catalyzed by BOD, depended on the temperature and pH of the electrolyte. The mediated ORR catalyzed by BOD on CCG electrode was also investigated using osmium based redox polymers. The catalytic current on the CCG electrode modified with 0.2 mg cm−2 of hydrogel consisting of an enzyme, a redox polymer and a cross linker, was 1.8 mA cm−2, which was almost five times higher than that on a flat glassy carbon electrode for the same hydrogel composition and loading. The catalytic current linearly increased with the total amount of hydrogel on the porous carbon electrode while the catalytic current on the flat electrode was indifferent to the loading.