Direct electron transfer at cellobiose dehydrogenase modified anodes for biofuel cells

Cellobiose dehydrogenases (CDHs, EC 1.1.99.18) contain a larger flavin-associated (dehydrogenase) domain and a smaller heme-binding (cytochrome) domain. CDHs from basidiomycete fungi oxidize at an appreciable level cellobiose, cellodextrins, and lactose, and those from ascomycetes may additionally oxidize some monosaccharides to their corresponding lactones at the flavin domain. CDHs are able to communicate directly with an electrode via their heme domain. In this work, different types of CDHs have been adsorbed on graphite electrodes and studied with respect to their direct electron transfer (DET) properties. Electrochemical studies were performed in the presence and absence of single-walled carbon nanotubes (SWCNTs) using lactose as substrate. In the presence of SWCNTs, the electrocatalytic current for substrate oxidation based on DET between enzyme and electrode was significantly increased. Furthermore, the onset of the electrocatalytic current was at lower potential than in the absence of SWCNTs. The highest electrocatalytic activity toward oxidation of lactose was found for CDH from the basidiomycete Phanerochaete sordida. Based on CDH from Phanerochaete sordida, an anode for biofuel cells was developed. This anode using lactose as substrate was combined with a Pt black cathode for oxygen reduction as a model for a membrane-less biofuel cell in which the processes at both electrodes occur by DET.