Electrochemical determination of nicotinamide adenine dinucleotide and hydrogen peroxide based on poly(xanthurenic acid), flavin adenine dinucleotide and functionalized multi-walled carbon nanotubes

A bifunctional sensor for determination of reduced β-nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H₂O₂) has been successfully fabricated by xanthurenic acid (Xa), flavin adenine dinucleotide (FAD), and functionalized carbon nanotubes (CNTs). The hybrid composites can be easily prepared by the electrocodeposition of polyXa/FAD and the adsorption of functionalized CNTs. These composites can be constructed of "polyXa/FAD/CNTs" and "CNTs/polyXa/FAD" according to the immobilization order of polyXa/FAD "before" and "after" the adsorption of CNTs. They are surface-confined and stable in various scan rates and different pH conditions. Particularly, the polyXa/FAD/MWCNTs show more efficient activity to target species due to the compact structure and more active surface area. It provides linear concentration range of 5 × 10 ^-6-1.7 × 10^-4 M and 1 × 10^-4-2.9 × 10^-3 M, with sensitivity of 155 μA mM^-1 cm ^-2 and 60 μA mM^-1 cm^-2, and detection limit of 10^-6 M and 10^-4 M (S/N = 3) for NADH and H ₂O₂, respectively. No interference except of the case for NADH determination in the presence of AA. It can be a good electrocatalyst to determine NADH and H₂O₂ and the linear sweep voltammetry (LSV) technique can help to analyze NADH from the AA interference.