Poly-xanthurenic acid as an efficient mediator for the electrocatalytic oxidation of NADH

Investigating the Electrocatalytic Oxidation of Dihydronicotinamide Adenine Dinucleotide at Nitrogen-Doped Carbon Nanotube Electrodes: Implications to Electrochemically Measuring Dehydrogenase Enzyme Kinetics

“…The k obs values show a concurrent increase with potential at any given concentration, but a decreasing k obs with increasing NADH concentration at the same potential. The inverse relationship of the rate constant to NADH concentration at a constant potential has also been observed at MWCNT electrodes modified with 2,3,5,6-tetrachloro-1,4-benzoquinone, polyxanthurenic acid, and 3,5-dinitrobenzoic acid, or SWCNT electrodes modified with Nile Blue or poly­(phenosafranin) . The aforementioned electrodes all used mediators, often called chemically modified or mediator-modified electrodes.…”

“…The mass transfer limiting current at a RDE is defined by the Levich equation, shown below: where i mt is the mass transfer limiting current, n is the number of electrons transferred ( n = 2), F is Faraday’s constant (96,485 C/mol), A is the electrode area, ω is the angular velocity (ω = 2πf; f is frequency), ν is the kinematic viscosity of the solvent (water in this case, 0.01 cm 2 /s), C is the concentration of NADH, and D is the diffusion coefficient. The diffusion coefficient was selected as 3.0 × 10 –6 cm 2 /s based on literature references. ,,− The measured current ( i ) may not align with i mt if the reaction is limited by the electron transfer kinetics rather than mass transport. In this case, a plot of i vs ω 1/2 should yield an asymptote approaching the kinetically limiting current i K .…”

“…The general enzymatic reaction for a NAD + -dependent dehydrogenase is shown below: The reduced cofactor, dihydronicotinamide adenine dinucleotide (NADH), can be reoxidized at an electrode surface via a 2-electron one-proton oxidation shown below: The formal potential of the NADH/NAD + couple is low, at −0.96 V vs Hg/Hg 2 SO 4 (−0.52 vs Ag/AgCl; −0.56 vs SCE; −0.32 vs NHE) and requires a large overpotential in order to be observed at conventional electrodes such as Pt or carbon. In order to lower the overpotential, mediators or catalysts are employed. , CNTs have been shown to be electrocatalytic toward NADH oxidation by substantially lowering the overpotential compared to conventional glassy carbon. − Often, CNTs are coupled with mediators to further lower the oxidation overpotential. − Mediators are polymerized on the CNT surface, or dispersed within a polymer, biopolymer, or hydrogel matrix to effectively couple the individual components and create a biocompatible environment for enzyme immobilization. − Heteroatom-doped CNTs, both B-CNTs and N-CNTs, have been shown to further decrease the oxidation overpotential compared to nondoped CNTs, without additional mediation. Although many reports have touted the benefits of CNTs for NADH oxidation, or demonstrated their use with dehydrogenases, the electron transfer kinetics of the electrochemical reaction are often neglected.…”

A New Highly Sensitive Electrochemical Biosensor for Ethanol Detection Based on Gold Nanoparticles/Reduced Graphene Oxide/Polyallylamine Hydrochloride Nanocomposite

“…Mediators can catalyze the electrochemical oxidation of coenzymes at a higher efficiency in the presence of nanomaterials [3,5,6,18,19]. Conductive polymers or polyelectrolytes are also very effective for preparing composite materials with improved properties in detecting NADH at lower potential and high reaction rates [20][21][22][23][24][25]. The integration of gold nanoparticles [25][26][27][28][29] or ionic liquids [30,31] was also successfully realized to develop composites used as electrode materials in detecting NADH.…”