Nitrobenzoic Acid-Functionalized Nanomaterials for Enzyme Immobilization

Enzymatic biofuel cells are devices that convert chemical energy into electrical energy thanks to electrochemical reactions taking place at the negative and the positive electrodes. They can be used as self-powered biosensors (analyte or inhibitor detection/quantification) or energy storage (biocapacitor or bioenergy generator). Their performances are highly dependent on the electrode material and the electron transfer capabilities of the biocatalysts. This chapter describes two different approaches that serve in increasing the amount of biocatalysts with a proper orientation at the molecular level in order to achieve direct electron transfer mechanism at the electrode interface. Specifically, two multicopper oxidases commonly used as the bioelectrocatalysts in oxygen reducing biocathodes of enzymatic fuel cells are targeted. The methodologies for surface modification take good use of conductive carbon- and gold-based nanomaterial to increase surface/volume ratio, to maintain high conductivity and with wide variety of chemical approach for their functionalization. The tridimensional structures of these proteins (steric hindrance, coulombic charges, etc.) are also essential points to consider to maximize biocatalyst immobilization. The synthesis, electrode preparations, and their physicochemical characterization are described, and their electrocatalytic performances are presented. When supplied with pure O₂, these enzymatic biocathodes are able to sustain continuous electrocatalytic current densities for oxygen reduction reaction at high potential.