Facile and tunable functionalization of carbon nanotube electrodes with ferrocene by covalent coupling and π-stacking interactions and their relevance to glucose bio-sensing

Ferrocene derivatives were π-stacked or covalently grafted onto a film of carbon nanotubes (CNTs) in order to determine the most effective method to immobilize redox centres on those high-surface area electrodes for sensors or catalytic applications. The immobilization of the ferrocene moiety via π–π interactions was done with a new ferrocene derivative bearing a pyrene group. The covalent grafting on the film of CNTs was achieved in two steps via the electroreduction of an aminoethylbenzenediazonium salt followed by post-functionalization with an activated ester derivative of ferrocene. Cyclic voltammetry and XPS measurements showed respectively that, in our conditions, the covalent grafting route gave more redox centres fixed on CNTs than the π-stacking one and the probes are located differently on the electrodes. In the first case, the high specific area of the CNTs electrodes resulted in a 32-fold increase of the amount of immobilized redox species with respect to its projected plane surface. Finally, a preliminary activity test of our π-stacked and covalently functionalized electrodes on glucose sensing was realized.