Soluble Carbon Nanotubes Used as Building Blocks of Biosensores

D. ACEVEDO; J. BALACH; M. C. MIRAS; C. BARBERO

San Carlos de Bariloche

Workshop; PASI: Bioinspired Nanoscience and Molecular Machines; 2005

Since their discovery in 1991[1], carbon nanotubes (CNT), have attracted many scientist in the field of physics, chemistry and material science due to their unique properties as well as their promise in the area of material chemistry [2,3]. One promising application of CNTs is their use in chemical sensors and nanoscale electronic device. Such potential application would greatly benefit from the ability of CNT to promote the electron transfer reaction of important biomolecules, including cytochrome c [4], NADH [5] , catecholamine neurotransmitters [6], or ascorbic acid [7]. Other application is the reaction of CNT in homogeneous solution with biological species, for example, the immobilization of oligonucleotides, enzymes, and proteins on it. In principle, it seems possible to build an electrochemical nanobiosensor using one nanotube with and attached enzyme molecule. To build electrochemical devices, the nanotubes should be deposited onto conventional electrode materials (glassy carbon, ITO), from nanotube solutions or stable dispersions. We propose to functionalize CNTs using two different synthetic methods to improve solubility and make it suitable for a wide range of applications. One method involves covalent modification by Gomberg reaction of the aromatic rings of the CNT with diazonium salts [8]. The other imply the non-covalent wrapping of soluble conductive polymers [9]. In the later method we use combinatorially modified polyanilines where a wide variety of polymers is available. The CNTs were functionalized and their solubility in different solvents were tested. Thin films of CNTs were then deposited by evaporation of the solvent on ITO or glassy carbon electrodes. The electrochemical response hydrogen peroxide, a relevant redox analyte produced by various enzymes, is then tested. The products of the reaction were identified by Differential Electrochemical Mass Spectroscopy (DEMS). Since the functionalized CNTs bear charge, the self assembly of CNT/polyelectrolyte multilayers was also tried. It was found that it is possible to assemble multilayers where the faradaic current of H2O2 oxidation increase with the number of layers, indicating that the layers are connected and active.