Enhancing electro-codeposition and electrocatalytic properties of poly(neutral red) and FAD to determine NADH and H2O2 using amino-functionalized multi-walled carbon nanotubes

Abstract

A bifunctional biosensor of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H₂O₂) has been successfully fabricated using amino-functionalized multi-walled carbon nanotubes (amino-MWCNT) as a template to immobilize neutral red (NR), poly(neutral red) (PNR), and flavin adenine dinucleotide (FAD). Sharp redox peaks indicate that the use of amino-MWCNT can improve the electro-codeposition of NR, PNR and FAD on the electrode surface. The hybrid composite can effectively lower the overpotential to 0.05 V and −0.1 V (vs. Ag/AgCl) for NADH and H₂O₂, respectively. The kinetic constant (k_kin) of 1.6 × 10⁴ M⁻¹ s⁻¹ and 2 × 10⁵ M⁻¹ s⁻¹ is evaluated for NADH and H₂O₂, respectively. It shows linear concentration range of 1.3–933.3 μM and 1–2555 μM, sensitivity of 457.2 μA mM⁻¹ cm⁻² and 10.1 μA mM⁻¹ cm⁻², and a detection limit of 1.3 μM and 0.1 μM (S/N = 3), for NADH and H₂O₂, respectively. Recovery of 96.5–102% and relative standard deviation (R.S.D.) of <5% was obtained in bovine calf serum samples. It shows good selectivity avoiding interference of AA, DA, UA, glucose, galactose, fructose, and sucrose. It allows fabricating an active bifunctional biosensor of NADH and H₂O₂ due to simplicity, multifunction, low cost, low overpotential, high sensitivity, and high selectivity.