Electrocatalytic detection of nicotinamide coenzymes by poly(o-aminophenol)- and poly(o-phenylenediamine)-modified carbon paste electrodes

Carbon paste electrodes coated with poly(o-phenylenediamine) (PPD) and poly(o-aminophenol) conducting films were prepared by potential scan electropolymerization in aqueous solutions. Both polymer-modified electrodes exhibit an electrocatalytic effect on the NAD(P)H oxidation, the PPD-coated electrode showing a reduction of the overpotential by more than 400 mV compared to the bare electrode. Amperometric detection of NADH and NADPH at PPD-modified carbon paste electrodes, at applied potentials down to + 150 mV (AgAgCl), give linear responses to the coenzyme concentration up to 1.0 × 10−7 M, with a detection limit of 8.1 × 10−10 M. Mediatorless amperometric biosensors forethanol and lactate were constructed using alcohol dehydrogenase or lactate dehydrogenase and NAD+ dispersed into the bulk of the carbon paste electrode and covered by a PPD electropolymerized film, which prevents the aqueous soluble species from dissolving into the electrolyte solution. Both electrodes exhibit a fast and linear response to ethanol and lactate in the concentration range 1–40 μM, with detection limits of 5.1 × 10−7 and 7.5 × 10−7 M, respectively.