A rapid, sensitive and label-free sensor for Hg(II) ion detection based on blocking of cysteine-quenching of fluorescent poly(thymine)-templated copper nanoparticles

A simple, rapid, sensitive and label-free fluorescence sensor has been developed for Hg(II) ion detection on the basis of blocking of cysteine-quenching of fluorescent poly(thymine) (poly T)-templated copper nanoparticles (Cu NPs). Fluorescent Cu NPs as fluorescence probe were formed within 5 minutes under mild conditions by using T30 DNA as template. In the presence of cysteine, the fluorescence intensity of T30-templated Cu NPs was found to be quenched effectively, due to the formation of a coordination complex by the Cu-S metal-ligand bond between the Cu NPs and the cysteine. However, when Hg2+ was added, the more stable Hg-S bond was formed through the strong binding preference of cysteine toward Hg2+, causing the cysteine to be far away from the surface of T30-templated fluorescent Cu NPs and hence the fluorescence intensity recovered. Under the optimized conditions, the sensor achieved highly sensitive and selective detection of Hg2+ in the range from 0.5 nM to 100 nM and the detection limit was 0.1 nM. Furthermore, the label-free method was successfully applied in the detection of Hg2+ in lake water samples. Besides, the developed sensor also showed high selectivity, low cost, and simplified operation. Thus, it would hold considerable potential to construct a simple, selective and sensitive fluorescence platform for the detection of Hg(II) ions.