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

The preparation and electrochemical characterization of carbon paste electr odes modified with 1, 10-phenantroline-5,6-dione (phen-dione) complexes of Fe ([Fe(phen-dione)(3)](2+)) and Re ([Re(phen-dione)(CO)(3)Cl]) as well as their behavior as electrocatalysts towards the oxidation of NADH are descri bed. These modified electrodes exhibit redox responses very similar to thos e 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. Car bon paste electrodes modified with either of the complexes, exhibited poten t and persistent electrocatalytic activity towards NADH oxidation at potent ials around 0.0 V versus SSCE, which represents a dramatic diminution in th e 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 mu M (S/N = 3), linearity u p to 4.0 mM, a sensitivity of 174 nA mM(-1) and a stability of at least 8 d ays when stored at 4 degrees C. (C) 1999 Elsevier Science B.V. All rights r eserved.