Low-Potential Nicotinamide Adenine Dinucleotide Detection at a Glassy Carbon Electrode Modified with Toluidine Blue O Functionalized Multiwall Carbon Nanotubes

Abstract

The determination of β-nicotinamide adenine dinucleotide (NADH) is very important, because the NAD + /NADH couple is a cofactor system for a large number of dehydrogenase enzymes (>300) and a component of biomarker systems.1 However, the direct oxidation of NADH at a bare electrode surface is highly irreversible, and needs a considerable overpotential (>1 V), 2,3 which is increased further by the presence of an enzyme. One of the most serious problems resulting from a high overpotential detection is fouling of the electrode surface associated with the accumulation of reaction products. 4 Much effort was devoted to pursuing new electrode materials and methods to decrease the detection potential and to avoid electrode surface fouling. One of the recently emerged and efficient ways to circumvent a high overpotential for the oxidation of NADH was to use carbon nanotubes (CNTs), since CNTs could significantly reduce the NADH overpotential, 5-10 although the decrease was not adequate.Another conventional approach to lower the oxidation potential of NADH is to apply redox mediators with low formal potentials. 11 Phenothiazine derivatives, such as azure (AZU) dyes, were usually utilized in this respect, because they are chemically reactive and display negative formal potentials (vs. SCE) at neutral pH. NADH detectors were developed based on AZU dyes that have been either adsorbed, 12 electropolymerized 13,14 or covalently attached 15 to the electrode surface. However, such modified surfaces displayed a rather limited stable ability and redox mediation capacity. The integration of phenothiazine derivatives and MWNTs in a polymeric matrix 16,17 for the determination of NADH with enhanced electrocatalytic characteristics was also reported, but the reported method was somewhat complicated. Hence, pursuing a simpler approach and new electrode materials to further decrease the overpotential for NADH oxidation and to minimize surface passivation effects to improve the detection sensitivity and redox mediation capacity is still an obvious challenge.In recent years, increasing interests have been focused on the rational functionalization of CNTs to fabricate functional nanostructures with novel properties. Some creative methods were used for the functionalization of CNTs with polymers, 18,19 biomolecules, 20,21 metal nanoparticles 22,23 and polynuclear aromatic compounds 24,25 through a covalent or noncovalent interaction. These functionalization strategies have generated many new materials with excellent functions, which are very attractive for practical applications. 26,27We describe here a simple method for constructing a new electrochemical functional nanostructure of TBO-MWNTs, which is based on a redox mediator, TBO assembled onto the surface of a MWNTs modified glassy carbon electrode. In this case the MWNTs act as a support of the redox mediator as well as a catalyst. The experimental results showed that the TBOMWNTs modified GC electrodes exhibited excellent electrocatalytic activity toward the oxidation of NADH. To the...

A Simple and Effective Way to Integrate Nile Blue Covalently onto Functionalized SWCNTs Modified GC Electrodes for Sensitive and Selective Electroanalysis of NADH

“…The LOD and dynamic range of our NADH biosensor are superior to those reported so far with the GC electrodes modified with redox mediators and CNTs [32,39]. The operational potential (À 0.1 V) is also very low and is comparable with that in literatures [25,40]. An excellent selectivity of the present modified electrode for NADH is demonstrated in Figure 5B, in which amperometric responses are given typically for the relevant physiological levels (0.1 mM) of NADH, ascorbic acid (AA), dopamine (DA) and uric acid (UA).…”

Antigout Effects of Plantago asiatica: Xanthine Oxidase Inhibitory Activities Assessed by Electrochemical Biosensing Method

“…The XOD casted onto the surface of DCNTs (right) did not change the morphology of DCNTs except that the brightness was slightly weakened, which may have been caused by XOD. Such small bundles and single nanotubes homogeneously distributed on GCE and twisted with XOD were expected to be very attractive for detecting electron transfer signal from the enzymatic and electrochemical reaction, yielding a high signal-to-noise ratio [ 18 ] for the evaluation of the XOD inhibitory effect of natural products.…”

“…Xanthine oxidase (XOD) (EC1.17.3.2, 12.1 U/mg) was obtained from the Nanjing Jiancheng Bioengineering Institute (Nanjing, China). Shorted double-wall carbon nanotubes (DCNTs) with 95% purity were purchased from Shenzhen Nanotech Port Co. (Shenzhen, China) and purified by refluxing the as-received DCNTs in 2.6 M HNO 3 for 10 h [ 18 ]. Xanthine and allopurinol were purchased from Sigma (St. Louis, MO, USA).…”

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

“…This mediator was demonstrated to shuttle the electron transfer between the immobilized diaphorase and the CNTP electrode, thus, showing a good electrocatalytic activity towards NADH oxidation at potentials around +0.2 V versus Ag|AgCl, where interfering reactions are less prone to occur. Zeng et al [50] described a glassy carbon electrode modified with Toluidine Blue O functionalised multiwall carbon nanotubes for lowpotential detection of NADH, with a wide linear range (from 2.0 M to 3.5 mM). Also, Chakraborty and Retna Raj [51] proposed a composite electrode, based on chitosan and Meldola Blue, which applied working potential was 630 mV less positive than that on an unmodified glassy carbon (GC) electrode.…”