Electrocatalytic determination of NADH by means of electrodes modified with MWCNTs and nitroaromatic compounds

Abstract In this work, we have both synthesized and studied 4-phenylbutyl-3,5-dinitrobenzoate (3,5-DNBPh) as a potential precursor of an electrocatalytic mediator for the oxidation of NADH, with the di-nitro compound immobilized in a three-dimensional network of glassy carbon electrodes modified with MWCNTs. This di-nitro compound is activated electrochemically to selectively generate one nitroso-hydroxylamine redox pair, which ultimately acts as a redox mediator of NADH oxidation. Thus, NADH electrocatalysis displaces the oxidation potential of NADH with the formation of a single voltammetric peak, the displacement occurs from Ep = + 0.374 V in GCE/MWCNT to + 0.001 V in GCE/MWCNT/3,5-DNBPh (very close to 0 V, ΔEp = 0.373 V). The 4-phenylbutyl-3,5-dinitrobenzoate mediator is sensitive to NADH concentration, and a linear regression between 0.1 and 0.6 mM NADH (r2 = 0.99) was obtained, with a detection limit of 22.3 μM (S/N = 3) and a quantification limit of 74.2 μM (S/N = 10). The developed modified electrode presents low NADH electrocatalytic oxidation potentials, and an interesting and novel advantage is that the preparation of the electrodes is fast, clean and effective, allowing biosensors to be obtained in a few steps.