Detection of NADH via electrocatalytic oxidation at single-walled carbon nanotubes modified with Variamine blue

Screen-printed electrodes (SPEs) modified with Variamine blue (VB), covalently attached to the oxidized single-walled carbon nanotubes (SWCNTs-COOH), were developed and used as chemical sensors for the detection of the reduced nicotinamide adenine dinucleotide (NADH). The Variamine blue redox mediator was covalently linked to the SWCNTs-COOH by the N,N'-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) chemistry. Infrared Fourier transform (IFT-IR) spectroscopy revealed the presence of the amide bands situated at 1623 cm(-1) (I band), 1577cm(-1) (II band) and 1437cm(-1) (III band) demonstrating the covalent linkage of Variamine blue to SWCNTs-COOH. The heterogeneous electron transferrate, k(abs), was 13,850 M-1 s(-1), and the k(s) and alpha were 0.8 s(-1) and 0.56, respectively. The pH dependence was also investigated. SPEs modified with Variamine blue by using the DCC/NHS conjugation method, showed a variation of -36 mV per pH unit. A successful application was the development of a lactate biosensor obtained by the immobilization of the L-lactate dehydrogenase on the NADH sensor. (C) 2007 Elsevier Ltd. All rights reserved.