Mediated electrocatalytic oxidation of bioanalytes and biosensing of glutamate using functionalized multiwall carbon nanotubes-biopolymer nanocomposite

The electrochemical and electrocatalytic properties of functionalized multiwall carbon nanotubes (FCNTs)-biopolymer nanocomposite is described. The multiwall carbon nanotubes (MWCNTs) were functionalized by sonochemical treatment in acidic solution. Sonochemical treatment shortens the length of MWCNTs and generates quinone-like functional group on the tube ends. The FCNTs were characterized by FTIR, FESEM and electrochemical measurements. The nanocomposite was prepared by mixing FCNTs with the biopolymer chitosan (CHIT). The nanocomposite-modified electrode shows a well-defined redox peak at -0.05 V. The voltammetric peak shifts by -59 +/- 1 mV while changing the solution pH by one unit, suggesting that protons and electrons take part in the redox reaction in the ratio of 1:1. The redox response of the nanocomposite-modified electrode is ascribed to the quinone-like functional groups of FCNT. The surface coverage of the redox species was 1.3 x 10(-10) mol/cm(2). The existence of quinone-like functional groups on the FCNTs was confirmed by FTIR spectral measurement. The mediated electrocatalytic oxidation of NADH and ascorbate (AA) by the FCNT nanocomposite-modified electrode was observed for the first time at less positive potential (-0.05 V) in the absence of any additional redox mediators. The oxidation potential for NADH and AA on the FCNT nanocomposite-modified electrode is much less positive than that on the as-purchased MWCNT niodified-electrode. Compared with the as-purchased MWCNTs, the FCNTs exhibit very high catalytic activity toward oxidation of the bioanalytes. The high catalytic activity is attributed to the presence of mediating quinone-like functionalities. The FCNT nanocomposite electrode was successfully used for the development of dehydrogenase based glutamate biosensor. (C) 2007 Elsevier B.V. All rights reserved.