title: Mediatorless voltammetric oxidation of NADH and sensing of ethanol.
abstract: A simple, selective and sensitive method for the detection of NADH and ethanol is presented. Self-assembled monolayers (SAMs) of mercaptopyrimidine (MPM) and their derivatives, thiocytosine (TC) and 4,6-diamino-2-mercaptopyrimidine (DMP) on gold (Au) electrode are used for the voltammetric detection of NADH and ethanol in neutral aqueous solution. A decrease of 200-300 mV in the overpotential associated with an observable increase in the peak current was obtained for the oxidation of NADH on MPM and TC monolayer-modified electrodes without any redox mediator. The facilitated electron transfer for the oxidation of NADH at the TC monolayer is ascribed to the existence of stable cationic p-quinonoid form of TC. The electrode modified with DMP monolayer could not exhibit stable response for NADH owing to the fouling of electrode surface. The MPM and TC monolayer-modified electrodes show high selectivity and excellent sensitivity (MPM: 0.633+/-0.005 microA cm(-2) microM(-1); TC: 0.658+/-0.008 microA cm(-2) microM(-1)) towards NADH with detection limit (3sigma) of 2.5 and 0.5 microM, respectively. Presence of large excess of ascorbate (AA) does not interfere the detection of NADH and the monolayer-modified electrode shows individual voltammetric peaks for AA and NADH. Voltammetric sensing of ethanol using alcohol dehydrogenase on MPM and TC monolayer-modified electrode is successfully demonstrated and these electrode can detect as low as 0.5 mM ethanol in neutral pH. The sensitivity of the MPM and TC monolayer-modified electrodes toward ethanol was found to be 3.24+/-0.03 and 3.435+/-0.04 microA cm(-2) mM(-1), respectively.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, West Bengal, India. crraj@chem.iitkgp.ernet.in
authors.forename: C Retna
authors.initials: CR
authors.lastname: Raj
authors.forename: S
authors.initials: S
authors.lastname: Behera
mesh_terms: D000327:Adsorption; D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods*; D003432:Cross-Linking Reagents; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D004800:Enzymes, Immobilized / Q000737:chemistry; D000431:Ethanol / Q000032:analysis* / Q000737:chemistry*; D009243:NAD / Q000737:chemistry*; D010084:Oxidation-Reduction; D011485:Protein Binding; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D003432:Cross-Linking Reagents; D004800:Enzymes, Immobilized; D009243:NAD; D000431:Ethanol