Integrated ethanol biosensors based on carbon paste electrodes modified with [Re(phen-dione)(CO)3Cl] and [Fe(phen-dione)3](PF6)2 Original Research Article

The preparation and electrochemical characterization of carbon paste electrodes modified with 1,10-phenantroline-5,6-dione (phen-dione) complexes of Fe ([Fe(phen-dione)3]2+) and Re ([Re(phen-dione)(CO)3Cl]) as well as their behavior as electrocatalysts towards the oxidation of NADH are described. These modified electrodes exhibit redox responses very similar to those of the complexes in aqueous solution, including the pH-dependent response ascribed to the pendant o-quinone groups, as well as to those observed for films of the complexes electrodeposited onto glassy carbon electrodes. Carbon paste electrodes modified with either of the complexes, exhibited potent and persistent electrocatalytic activity towards NADH oxidation at potentials around 0.0 V versus SSCE, which represents a dramatic diminution in the overpotential. Using carbon paste electrodes modified with the Re complex, alcohol dehydrogenase and NAD+ we have developed an integrated ethanol biosensor. It exhibited a detection limit of 45 μM (S/N = 3), linearity up to 4.0 mM, a sensitivity of 174 nA mM−1 and a stability of at least 8 days when stored at 4°C.