Ferrocenecarboxylic acid was adsorbed on a Nb2O5 film grafted on a porous SiO2 surface, resulting in a modified silica, presenting the following characteristics: amount of attached Nb2O5 = 0.58 mmol g(-1), amount of ferrocenecarboxylic acid (HOOCFeCp2) = 0.12 mmol g(-1) and specific surface area S-BET = 294 m(2) g(-1) with an average surface density delta = 0.23 molecules nm(-2) or an average intermolecular distance of 2 nm. The organometallic complex is adhered to the surface by forming the Nb-OOC bond and, thus, the electroactive species is not easily leached out from the surface under various oxidation-reduction cycles of the central metal in a cyclic voltammetry experiment. The midpoint potential, E,,, is observed at 0.29 V versus SCE and it remains practically unchanged in various supporting electrolyte solutions and also is not significantly affected by pH changes between 1 and 7.5. An electrode made with this material, SiNb-O2CFeCp2, mediates NADH oxidation at 0.35 V in solution at pH 6. Kinetics studies were evaluated by using the rotating disk electrode technique in order to understand the mechanism of NADH oxidation on the SiNb-O2CFeCp2 modified electrode. (C) 2001 Elsevier Science Ltd. All rights reserved.461624992505