In the present paper, we used single-stranded poly-T (100% thymine bases) and poly-C (100% cytosine bases) nucleic acids as DNA probes for selective and sensitive individual electrochemical determination of Hg2+ and Ag+, respectively on the multi-walled carbon nanotubes paste electrodes (MWCNTPEs) by using Fe(CN)6]3-/4- as electroactive labels. In the presence of Hg2+ and Ag+, the probe-Hg2+/Ag+ interactions through T-Hg2+-T and C-Ag+-C complexes formation could be formed a unimolecular hybridized probe. This structure of probe led to its partial depletion from electrode surface and facilitation of electron transfer between [Fe(CN)6]3-/4- redox couple and electrode surface, resulting in the enhanced differential pulse voltammetry (DPV) oxidation current of [Fe(CN)6]3-/4- at the probe modified electrode surface. We applied the difference in the oxidation peak currents of [Fe(CN)6]3-/4- before and after Hg2+/Ag+-DNA probe bonding (∆I) for electrochemical determination of these heavy metal ions. Detection limits were 8.0×10-12 M and 1.0×10-11 M for Hg2+ and Ag+ ions determination, respectively. The biosensors were utilized to determine the weight percent of toxic metals i.e., silver and mercury in dental amalgam filling composition. The results of their practical applicability in analysis of the amalgam sample were satisfactory.
