Anthracene-modified pyrenes immobilized on carbon nanotubes for direct electroreduction of O2 by laccase

Enhancement of direct bioelectrocatalysis of dioxygen reduction with laccase has been investigated using π-electron rich compounds, such as anthracene, for docking the laccase active site in close proximity to the electrode. These molecules have been shown to promote direct bioelectrocatalysis by orienting the enzyme to undergo fast, direct electron transfer. In this study, pyrene moieties have been covalently grafted to anthracene groups to be able to functionalize carbon nanotube walls to increase the number of binding sites on nanotubes for laccase. Current densities were compared to unmodified pyrene immobilized by non-covalent interactions on the hydroxylated carbon nanotubes (MWCNT-OH). The presence of pyrene derivatives leads to higher current density than regular MWCNT-OH. In both configurations, the covalent grafting of the anthracene group to pyrene improved electrocatalytic signals. Under normal aerated conditions, 1-pyrenemethanol-modified and 1-aminopyrene-modified electrodes produced 81.4 ± 14.5 μA/cm2 and 62.5 ± 4.9 μA/cm2, respectively, while for derivatives 1 and 2, current densities produced 186.4 ± 10.4 μA/cm2 and 153.0 ± 5.2 μA/cm2. Once characterized, the best pyrene-based bioelectrodes were used with laccase as a biocathode and combined with a glucose oxidase (GOx)-based bioanode to form glucose/O2 biofuel cells.