IntroductionQuantum dots (QDs), due to their variety of size-and shape-dependent optical and electrical properties [1,2], have been attracting extensive attention for numerous applications such as in biological labels, photovoltaic devices, and optoelectronic devices [3 5]. In particular, they are very attractive as QD-based optical sensors for detecting biomolecules, small molecules, and cations or anions due to their high fluorescence quantum yields, good photostability, and negligible photobleaching in comparison with dyes [6 10]. CdTe is an important semiconductor material and CdTe QDs show increasing promise due to their large exciton Bohr radius (7.3 nm) and narrow ABSTRACTA facile one-pot microwave irradiation reduction route has been developed for the synthesis of highly luminescent CdTe quantum dots using Na 2 TeO 3 as the Te source in an aqueous environment. The synthesis parameters of this simple and rapid approach, including the reaction temperature and time, the pH of the reaction solution and the molar ratio of the 3-mercaptopropionic acid (MPA) stabilizer to Cd 2+ , have considerable infl uence on the particle size and photoluminescence quantum yield of the CdTe quantum dots. The photoluminescence quantum yield of CdTe quantum dots prepared using relatively short reaction times (10 40 min) reached 40% 60% (emission peaks at 550 640 nm). Furthermore, the resulting products could be used as fl uorescent probes to detect Hg 2+ ions in aqueous media. The response was linearly proportional to the concentration of Hg 2+ ion in the range 8.0×10 9 mol/L to 2.0×10 6 mol/L with a detection limit of 2.7×10 9 mol/L.

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Mercuric ion (Hg 2+ ), released from both natural and industrial sources, has severe adverse effects on human health and the environment even at very low concentrations. It is very important to develop a rapid and economical method for the detection of Hg 2+ with high sensitivity and selectivity. Nanomaterials with unique size and shape-dependent optical properties are attractive sensing materials. The application of nanomaterials to design optical sensors for Hg 2+ provides a powerful method for the trace detection of Hg 2+ in the environment, because these optical sensors are simple, rapidly responsive, cost-effective and highly sensitive. This review summarizes the recent advances on the development of optical assays for Hg 2+ in aqueous solution by using functionalized nanomaterials (including noble metal nanoparticles, fluorescent metal nanoclusters, semiconductor quantum dots and carbon nanodots). Detection strategies based on the Hg 2+ -induced changes in spectral absorbance, fluorescence intensity and surface-enhanced Raman scattering signals were described. And the design principles for each optical assay were presented. In addition, the future challenge and the prospect of the development of nanomaterial optical sensors for Hg 2+ detection were also discussed.

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