Silver ion modulated CdS quantum dots for highly selective detection of trace Hg2+

In the present work, water-soluble cysteamine capped-CdS quantum dots (Cys-CdS QDs) modulated with Ag+ were employed as fluorescence sensors for the determination of Hg2+ ion. The synthesized Cys-CdS QDs exhibit relatively weak fluorescence emission, however, the emission was enhanced exclusively in the presence of Ag+ compared to other metal ions. Moreover, the fluorescence intensity of the Ag+ modulated Cys-CdS QDs (Ag+@Cys-CdS QDs) was significantly quenched in the presence of trace amounts of Hg2+ due to high-affinity metallophilic interactions between Hg2+ and Ag+. Based on this specific interaction, good selectivity towards the detection of Hg2+ over other metal ions was achieved. To gain the best sensing performance, parameters affecting the Hg2+ detection sensitivity were studied and optimized in detail. Under the optimized conditions, the fluorescence intensity of Ag+@Cys-CdS QDs decreased linearly with Hg2+ concentration in the range of 0.1-3.5 μM, with a limit of detection of around 0.09 μM. The applicability of this sensor was demonstrated by the determination of Hg2+ in drinking water samples, corresponding well with results of cold-vapor atomic absorption spectrometry.