We recently described nitro-fluorenone derivatives as possible redox mediators for NADH oxidation. Appropriate changes in their molecular structure, like the introduction of a carboxyl group, allow the specific complexation of the surface confined catalyst with NADH. using bivalent cations as a bridging unit. This results in up to 500% higher catalytic currents and a better stability of the modified electrode. At low overpotentials (-45 mV versus Ag / AgCl) a linear increase of catalytic current as a function of NADH concentration is observed between 2 muM and 2 mM. These results are very promising with regard to potential applications in the field of biosensors.