Abstract

In this paper, for the first time, an electro-analytical method based on the direct adsorption of double-stranded deoxyribonucleic acid (dsDNA) at glassy carbon electrode modified with ethylendiamine (eda) functionalized multi-walled carbon nanotubes (eda-CNT) is reported. The carbon nanotubes were functionalized with ethylendiamine via chemical modification of the carboxyl groups, and the eda-CNTs were characterized by different techniques, including Fourier transform infrared (FT-IR) spectroscopy, thermo gravimetric analysis (TGA), elemental analysis and cyclic voltammetry, and compared with pristine (CNT) and oxidized (ox-CNT) MWCNTs. The presence of eda on the CNT surface allows them to disperse in a phosphate buffer solution at pH 7.0 and provides an environment that promotes the electrostatic adsorption of dsDNA. At eda-CNTs, the adsorption of dsDNA is improved and a linear correlation between the oxidation current of guanine bases and the accumulation time is observed. This result indicates that the presence of positive charges on the surface of the nanotube plays an important role in the attraction of the dsDNA molecule. A more sensitive detection of DNA was obtained compared with CNT and ox-CNT when eda-CNT where used with a linear range from 5 to 60 ppm, a sensitivity of 0.0315 +/- 0.0003 mu A mg(-1) L and a LOD of 0.971 ppm after a 10-min accumulation which is lower than that obtained previously using cationic dispersing agents. The analytical performance reported is comparable with that reported previously for cationic polymers in terms of linear range and LOD values. (C) 2013 Elsevier B.V. All rights reserved.