Novel electrochemical DNA hybridization biosensors for selective determination of silver ions.

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 Pb(2+), Cu(2+), Ca(2+), Zn(2+), Fe(2+) and Hg(2+). The proposed biosensors were applied successfully to the voltammetric determination of Ag(+) in real samples.