A simple electrochemical DNA- based biosensor was designed for determination of Cd2+ using ethyl green (EG) as a DNA hybridization indicator on the surface of carbon paste electrode (CPE). The interaction of Cd2+ with double strand DNA (dsDNA) led to the destabilizing of dsDNA and the increase in the reduction peak currents of EG. The difference in the values of electrochemical responses of EG before and after DNA helix destabilization in the presence of Cd2+ (∆I) was used for Cd2+ determination and was linearly related to the concentration of Cd2+ over the ranges of 1.0 pM to 1.0 nM and 10.0 nM to 1.0 µM. Detection limit was achieved as low as 0.3 pM using simple and low cost working electrode and without applying any materials for modification of electrode or DNA. The proposed biosensor was utilized successfully to real sample analysis of Cd2+.
