An Ultrasensitive Fluorescence Method for Mercury Ion Detection Based on Mercury Nanoladder Signal Amplification and Thiazole Orange

Of all the heavy metals that contaminate tobacco, divalent mercuric ion is one of the most dangerous. Thus, a novel label-free and enzyme-free fluorescent method, based on mercury nanoladders integrated with thiazole orange (TO), was developed for rapid, sensitive, and selective detection of Hg2+ in aqueous solutions. In this study, we have determined that, in the presence of mercury ions, the thymine bases in probe 1 (P1) and probe 2 (P2) interact with Hg2+ to form a stable T-Hg2+-T structure, then long double helices of Hg2+ nanoladders will eventually result. Subsequently, the fluorescence of the TO dye was strongly enhanced, due to the binding of TO dye to long dsDNA. The increase in fluorescence intensity was linear with Hg2+ concentration in the range of 0.02-5 nM, and the limit of detection for this method was 20 pM. In addition, this method exhibits high selectivity, and experiments with tobacco samples also showed good results. We believe that the proposed system accurately and efficiently detects mercury ions within different substrates.