Effective NADH sensing by electrooxidation on carbon-nanotube-coated platinum electrodes

Abstract

Coatings of carbon nanotubes (CNTs) on conventional Pt electrodes enable sensing of NADH by fixed-potential amperometry without fouling and with high sensitivity and low detection limit. Effective electrochemical oxidation of NADH has been pursued aggressively for many years due to the utility of NAD+-dependent dehydrogenases in sensing, diagnostics, and chemical synthesis. Pt electrodes have not been explored for electrochemical NADH sensing in recent years due to reported problems with fouling. In this work, acid-treated, metallic, single-wall carbon nanotubes (SWCNTs) and untreated multiwall carbon nanotubes (MWCNTs) were explored as coatings for Pt disk electrodes to reduce fouling and to enhance electrochemical detection of NADH. The electrodes with CNT coatings were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and fixed-potential amperometry. A detection limit as low as 0.17μM was observed with the SWCNT coating at 0.7V (vs. Ag/AgCl) and 0.19μM with the MWCNTs at 0.5V. Average sensitivities of both preparations were ~370mAM−1cm−2. However, similar results were obtained with the MWCNT-coated electrodes at the much-reduced potential of 0.3V, which suggests a significant advantage of the MWCNT preparation that is worthy of further investigation. This study demonstrates the utility of relatively inert, conventional Pt electrodes with a simple CNT coating for effective NADH sensing at reduced potential without fouling.