Functionalized carbon nanotubes for bioelectrochemical applications: Critical influence of the linker

A series of covalently bonded ferrocene derivatives to carbon nanotubes via either alkyl or poly(ethylene glycol) (PEG) spacers has been prepared and deposited onto glassy carbon electrodes using chitosan as a binder. Evaluation of the effect of spacer arms revealed that the hydrophilic and flexible PEG chain greatly facilitates electron transfer reactions. When adding diaphorase in the composite, effective electrocatalytic oxidation of NADH was achieved. The PEG spacer also permitted an efficient dispersion of the functionalized carbon nanotubes, without additives. In this way, they can be easily incorporated in water-based sol–gel matrices, as illustrated for bioelectrochemical applications with co-immobilized glucose dehydrogenase, diaphorase and NAD+ cofactor.