In this work, novel electrochemical biosensors for Ag+ determination based on Ag+-induced DNA hybridization, using Ethyl green (EG) as an electroactive label on the surface of bare carbon paste electrode (CPE) and gold nanoparticles-modified carbon paste electrode (GN-CPE) are reported. Two single-strand poly-C (100% cytosine bases) DNAs are used as oligonucleotide probe and target. In the presence of Ag+, the target DNA with full cytosine-cytosine (C-C) mismatches could hybridize with the probe DNA by forming C-Ag+-C complex. The induced hybridization of the two oligonucleotides leads to the decrease in the reduction peak currents of EG, which could be used for electrochemical determination of Ag+. This difference in the values of the reduction peak current of EG before and after DNA hybridization (∆I) was linear with the concentration of Ag+ in the ranges from 3.0×10-10 to 1.0×10-9 mol L-1 and 9.0×10-11 to 1.0×10-9 mol L-1, for the biosensor and nanoparticles modified-biosensor, respectively. Calculated detection limits were 1.04×10-10 and 2.64×10-11 mol L-1 for biosensor and nanoparticles modified-biosensor, respectively. The biosensors demonstrated good selectivity towards Ag+ ions in the presence of some metal ions such as Pb2+, Cu2+, Ca2+, Zn2+, Fe2+ and Hg2+. The proposed biosensors were applied successfully to the voltammetric determination of Ag+ in real samples.
