Electrochemical Oxidation of Dihydronicotinamide Adenine Dinucleotide at Nitrogen-Doped Carbon Nanotube Electrodes

Nitrogen-doped carbon nanotubes (N-CNTs) substantially lower the overpotential necessary for dihydronicotinamide adenine dinucleotide (NADH) oxidation compared to nondoped CNTs or traditional carbon electrodes such as glassy carbon (GC). We observe a 370 mV shift in the peak potential (<i>E</i>_p) from GC to CNTs and another 170 mV shift from CNTs to 7.4 atom % N-CNTs in a sodium phosphate buffer solution (pH 7.0) with 2.0 mM NADH (scan rate 10 mV/s). The sensitivity of 7.4 atom % N-CNTs to NADH was measured at 0.30 ± 0.04 A M^–1 cm^–2, with a limit of detection at 1.1 ± 0.3 μM and a linear range of 70 ± 10 μM poised at a low potential of −0.32 V (vs Hg/Hg₂SO₄). NADH fouling, known to occur to the electrode surface during NADH oxidation, was investigated by measuring both the change in <i>E</i>_p and the resulting loss of electrode sensitivity. NADH degradation, known to occur in phosphate buffer, was characterized by absorbance at 340 nm and correlated with the loss of NADH electroactivity. N-CNTs are further demonstrated to be an effective platform for dehydrogenase-based biosensing by allowing glucose dehydrogenase to spontaneously adsorb onto the N-CNT surface and measuring the resulting electrode’s sensitivity to glucose. The glucose biosensor had a sensitivity of 0.032 ± 0.003 A M^–1 cm^–2, a limit of detection at 6 ± 1 μM, and a linear range of 440 ± 50 μM