Low overpotential detection of NADH and ethanol based on thionine single-walled carbon nanotube composite

A nanocomposite of thionine with single-walled carbon nanotubes (Th-SWNTs) was fabricated and the electrocatalytic oxidation of beta-nicotinamide adenine dinucleotide (NADH) by the nanocomposite was demonstrated. Th-SWNTs showed high electrocatalytic activity toward the oxidation of NADH, leading to a substantial decrease in the overpotential by more than 640 mV. The high electrocatalytic activity of Th-SWNTs resulted from the synergistic effects of SWNTs and a small amount of thionine polymer present on the nanocomposite. The electrocatalytic characteristics were described for biosensing application. The Th-SWNT-coated electrode allowed highly sensitive amperometric detection of NADH with a low limit of detection (2 mu M), low applied potential (50 mV vs saturated calomel electrode), and minimization of surface fouling. The ability of Th-SWNTs to promote electron transfer between NADH and the electrode suggests that the nanocomposite can be used as a biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model, a biosensor, ADH-Th-SWNT/glassy carbon, was constructed by a simple casting process. The biosensor showed rapid and highly sensitive response to ethanol with good stability, acceptable reproducibility, and higher biological affinity. Moreover, this biosensor can be used to determine ethanol concentration in real samples. The results presented in this work will promote the development of electrochemical research for enzymes, biosensors, biofuel cells, and other related bioelectronic devices. (C) 2008 The Electrochemical Society.