Bioelectrocatalytic oxygen reduction by bacterial laccase on electrodes modified with multi-walled carbon nanotubes

In this work, the electrochemical behaviour of bioelectrodes based on bacterial laccase Streptomyces carpinensis VKM Ac-1300 obtained using different immobilization methods was investigated. The bioelectrodes were formed by fixing the enzyme on the electrode surface by simple adsorption, by adsorption on the modified electrode by multi-walled carbon nanotubes and by covalent bounding of the enzyme by carboxyl groups with functionalized multi-walled carbon nanotubes. The orientation of immobilized laccase enzymes and their ability to direct and mediated electron transfer were assessed by direct amperometry at constant potential. It was found that, depending on the method of immobilization, from 5 to 10% of immobilized enzyme has the correct orientation and, consequently, the ability to direct electron transfer. At the same time, covalent bounding of protein on the surface of graphite electrodes modified with nanotubes leads to a more active direct electron transfer, an increase in the rate of oxygen reduction and long-term electrode stability. Thus, for bacterial laccase Streptomyces carpinensis VKM Ac-1300 the possibility of direct electron transfer at their immobilization by covalent bounding with carboxyl groups of multi-walled carbon nanotubes was shown. The developed bioelectrodes can be used as cathodes in biofuel cells.