Low-potential stable NADH detection at carbon-nanotube-modified glassy carbon electrodes
Introduction
β-Nicotinamide adenine dinucleotide (NADH) is involved as a cofactor in several hundred enzymatic reactions of NAD+/NADH-dependent dehydrogenases. The electrochemical oxidation of NADH has thus been the subject of numerous studies related to the development of amperometric biosensors [1], [2]. Problems inherent to such anodic detection are the large overvoltage encountered for NADH oxidation at ordinary electrodes [3] and surface fouling associated with the accumulation of reaction products [4]. Consequently, considerable effort has been devoted toward the goal of identifying new electrode materials that will reduce the overpotential for NADH oxidation and minimize surface passivation effects.
This article reports on the catalytic oxidation of NADH and highly stable amperometric NADH response at glassy carbon electrodes modified with carbon-nanotube (CNT) coatings. Carbon nanotubes represent exciting nanomaterials, constituted of graphitic carbon consisting of one or several concentric tubules [5]. Recent studies demonstrated improved electrochemical behavior of cytochrome c [6] and of catecholamine neurotrasmitters [7], [8] at nanotube-modified electrodes. The ability of carbon nanotubes to promote electron-transfer reactions has been attributed to their electronic structure and high electrical conductivity. Similarly, single-wall and multi-wall carbon-nanotubes (SWCNT and MWCNT)-modified glassy carbon electrodes are shown below to offer a marked decrease in the overvoltage for NADH oxidation and to circumvent NADH surface fouling effects during amperometric sensing. Such attractive redox behavior of NADH at carbon-nanotube-modified glassy carbon electrodes is reported in the following sections.
Section snippets
Apparatus
Amperometric experiments were performed with a Bioanalytical Systems (BAS) CV-27 voltammograph, in connection with a BAS X–Y recorder. Cyclic voltammograms were recorded with the Autolab PGSTAT10 Electrochemical Analyzer (Eco Chemie BV, Utrecht, Netherlands). The working electrode, the Ag/AgCl reference electrode (Model CHI111, CH Instruments, Austin, TX), and platinum wire counter electrode were inserted into the 20-ml cell (BAS, Model VC-2) through holes in its Teflon cover. A magnetic
Results and discussion
Fig. 1 compares cyclic voltammograms for NADH, recorded at 50 mV/s, at unmodified (A) and CNT-modified (B,C) glassy carbon electrodes. With the unmodified electrode, the oxidation results in broad peak, with a peak potential of +0.82 V. The nanotube-modified electrodes exhibit a substantial negative shift of the anodic peak potential and increased current signal. The catalytic activity is evident from the defined peaks at +0.33 V (B; MWCNT) and +0.36 V (C; SWNT). The oxidation process starts at
Conclusions
We have illustrated that carbon-nanotube-modified glassy carbon electrodes offer a stable low-potential amperometric detection of NADH. The CNT-coating offers a marked decrease in the overvoltage for the NADH oxidation and eliminates surface fouling effects. Such electrocatalytic activity and stability compare favorably to that observed at other carbon-electrode materials [1], [2]. While the electrocatalytic activity of CNT films has been reported in connection to other biomolecules [6], [7],
Acknowledgements
This work was supported by grants from NIH (J.W.) and Battelle PNNL LDRD Project (Y.L.) MM acknowledges the Islamic Development Bank (IDB) (Jeddah, SA) for a scholarship provided for the Ph.D. study.
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