Anthracene-Modified Multi-Walled Carbon Nanotubes as Direct Electron Transfer Scaffolds for Enzymatic Oxygen Reduction

The development of new methods to facilitate direct electron transfer (DET) between enzymes and electrodes is of much interest because of the desire for stable biofuel cells that produce significant amounts of power. In this study, hydroxylated multiwalled carbon nanotubes (MWCNTs) were covalently modified with anthracene groups to help orient the active sites of laccase to allow for DET. The onset of the catalytic oxygen reduction current for these biocathodes occurred near the potential of the T1 active site of laccase, and optimized biocathodes produced background-subtracted current densities up to 140 mu A/cm(2). Potentiostatic and galvanostatic stability measurements of the biocathodes revealed losses of 25% and 30%, respectively, after 24 h of constant operation. Finally, the novel biocathodes were utilized in biofuel cells employing two different anodic enzymes. A compartmentalized cell using a mediated glucose oxidase anode produced an open circuit voltage of 0.819 +/- 0.022 V, a maximum power density of 56.8 (+/- 1.8) mu w/cm(2), and a maximum current density of 205.7 (+/- 7.8) mu A/cm(2). A compartment less cell using a DET 'fructose dehydrogenase anode produced an open circuit voltage of 0.707 +/- 0.005 V, a maximum power density of 34.4 (+/- 2.7) mu W/cm(2), and a maximum current density of 2017. (+/- 14.4) mu A/cm(2).