An approach for electrochemical functionalization of carbon nanotubes/1-amino-9,10-anthraquinone electrode with catechol derivatives for the development of NADH sensors

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A new type of modified electrode, consisting of electro generated quinone redox mediator and carbon nanotubes (CNT) for electrocatalytic oxidation of reduced form of β-nicotinamide adenine dinucleotide (NADH) has been developed. The CNT functionalized with 1-amino-9,10-anthraquinone electrodes (GC/CNT/AAQ) were subjected to cyclic voltammetry in the presence of selected 1,2-dihydroxybenzene derivatives (catechol, 3-methoxycatechol and 4-methylcatechol). As a result, the electroactive quinone adducts were synthesized directly on the electrode surface via Michael addition mechanism. The structures of novel compounds were established using complementary computational studies and then were confirmed by HPLC-ESI-MS method. Electrochemical characterization of the electrodes after modification was carried out by cyclic voltammetry in broad range of pH. The heterogeneous electron transfer rate constants (ks) for the studied quinone modified electrodes were estimated and the obtained values (between 9.8 and 16.7 s−1) suggest moderate electron transfer kinetics. The electrodes displayed remarkable catalytic activity toward NADH oxidation in neutral phosphate buffer (pH = 7.4). The incorporation of quinone moieties onto electrode surface resulted in significantly decreased oxidation potential and enhanced current as compared to unmodified electrodes. NADH has been successfully determined at 0.1 V vs. Ag/AgCl, on all developed electrodes. The established method is characterized by linearity, low limits of detection (from 0.63 to 1.15 μM) and quantitation (from 1.9 to 3.47 μM), high sensitivity, suitable accuracy, repeatability and precision.