Functionalization of carbon nanotubes for direct electrochemistry of horseradish peroxidase

New strategies for functionalization of carbon nanotubes (CNTs) for facilitating direct electron transfer of horseradish peroxidase (HRP) are reported. The CNTs are covalently functionalized with hydroxyl and carboxyl groups and noncovalently functionalized with block copolymer (Pluronic P123). The functionalized CNTs are found to possess all improved solubility in aqueous solution and may have an enhanced biocompatibility with biomacromolecules such as proteins and enzymes. Moreover, all the functionalized CNTs have been demonstrated for the first time to be capable of facilitating the direct electron transfer of HRP, in which the noncovalently P123-functionalized CNTs are shown to be advantageous over those covalently functionalized with -OH and -COOH groups. The catalytic activities of HRP adsorbed onto the P123-functionalized CNTs towards the reductions of dioxygen (O-2) and hydrogen peroxide (H2O2) are also discussed.