Photoluminescence Quenching Based Visual and Spectroscopic Method for Mercury Sensing by Surface-Modified Cadmium Sulphide Quantum Dots.

Abstract

Here we present a simple yet efficient analytical method for sensing ultratrace levels of Hg2+ ions by highly water soluble CdS quantum dots functionalized with thiourea as a probe. The bluish photoluminescence emission of the probe responded to a systematic linear photoluminescence quenching in the presence of increasing concentration of Hg2+ ions. The photoluminescence quenching by Hg2+ ions was attributed to agglomeration of the quantum dots, which has been confirmed by zeta potential measurements. The sensitivity (31.38 L/mg) and LoD (0.11 μg/L) of Hg2+ ion detection by our method are two folds improved with respect to the existing data of CdS as sensor. The improved detection is attributable to synthesis of less than 3 nm diameter CdS quantum dots which rendered very high water solubility and hence facilitated better interaction with Hg2+ ions. The detection of Hg2+ ion was free from most interfering cations and anions, except for minor interference from Cu2+ and Pb2+ corresponding their concentrations expected in ground water. Further, the scope for visual detection of Hg2+ was explored, which revealed naked eye recognizable photoluminescence quenching of the probe treated 0.3 mg/L of Hg2+ ion when excited by a light source of 365 nm. The suitability of our probe to analyze Hg2+ in real samples has been demonstrated by Hg2+ spike analysis in groundwater and river water samples.