Integrated Enzyme-Based Biofuel Cells-A Review

Enzyme-based biofuel cells provide versatile means to generate electrical power from biomass or biofuel substrates, and to use biological fluids as fuel-sources for the electrical activation of implantable electronic medical devices, or prosthetic aids. This review addresses recent advances for assembling biofuel cells based on integrated, electrically contacted thin film-modified enzyme electrodes. Different methods to electrically communicate the enzymes associated with the anodes/cathodes of the biofuel cell elements are presented. These include: (i) The reconstitution of apoenzymes on relay-cofactor monolayers; assembled on electrodes, or the crosslinking of cofactor-enzyme affinity complexes assembled on electrodes. (ii) The immobilisation of enzymes in redox-active hydrogels associated with electrodes. (iii) The use of nano-elements, such as carbon nanotubes, for the electrical contacting of the enzyme electrodes comprising the biofuel cells. All three methods are implemented for the electrical contacting of oxidases and dehydrogenases with electrodes acting as anodes of biofuel cells, and for the electrical wiring of bilirubin oxidase, cytochrome oxidase, and laccase with electrodes, that yield the cathode units of the biofuel cells. Different methods-to control the biofuel cells, operation by external stimuli are discussed, including the application of external magnetic fields, and the electrochemical switching of the biofuel cell operation.