A metallacarborane redox mediator for an enzyme-immobilized chitosan-modified bioanode

We describe here the first report of a metallacarborane complex as a redox mediator in a functioning biofuel cell. Specifically, we have prepared a water-soluble salt of the complex anion [commo-3,3'-Fe-(closo-2,1-C2B9H11)(2)](-) and employed it as a redox mediator for glucose oxidation using chitosan/multiwalled carbon nanotube-modified electrodes comprising immobilized glucose oxidase. Experiments have indicated an increased amperometric response to glucose feeding, providing the complex mediator was initially supplied in the phosphate buffer electrolyte solution. Cathodic peak currents increased to a maximum of 1.24 mA/cm(2) up to the saturating threshold concentration of glucose, indicating a significant degree of metallacarborane-enzyme communication and supporting the notion of a proposed metallacarborane redox mediator in biofuel cells. Upon incorporation of the mediator by anion exchange in the chitosan with the enzyme prior to measurement, however, an attenuated response to glucose feeding was detected, despite efforts to use different tactics to cast such films on the electrode such as a bilayer scheme. It is believed that the uptake of significant quantities of the metallacarborane into the chitosan is sponsoring a gross change in the microstructure of the biopolymer. This is supported by SEM imaging of the metallacarborane-modified chitosan, which revealed a remarkable transformation of the biopolyrner scaffold. (C) 2009 Elsevier B.V. All rights reserved.