Highly sensitive and selective detection of Hg2+ using mismatched DNA and a molecular light switch complex in aqueous solution

A novel “signal-on” assay for sensitive and selective detection of Hg2+ in aqueous solution based on mismatched DNA and a molecular light switch complex, [Ru(phen)2(dppz)]2+, was reported in the present work. This Hg2+ specific sensor system composed of two label-free DNA probes with eight T–T mismatches, which could form stable DNA duplexes by thymine–Hg2+–thymine (T–Hg2+–T) in the presence of Hg2+. The luminescence of [Ru(phen)2(dppz)]2+ is very weak in aqueous solution, and significant luminescence can be observed when intercalating into DNA duplexes. By monitoring Hg2+-dependent luminescence intensity enhancement, highly sensitive and selective determination of Hg2+ has been achieved. Under the optimum conditions, the luminescence intensity was proportional to the concentration of Hg2+ in the range of 1.0 × 10−9–1.5 × 10−7 M. A detection limit of 3.5 × 10−10 M Hg2+ was achieved using 3σ. The presence of other metal ions did not interfere with the detection of Hg2+ even at high concentrations. This approach is simple and rapid, which can be used to monitor the Hg2+ concentration in drinking water and natural media within 30 min.