Hydrophilic ionic liquid-passivated CdTe quantum dots for mercury ion detection

A hydrophilic ionic liquid, 1-ethyl-3-methylimidazolium dicyanamide (EMIDCA), was used as a medium for the synthesis of highly luminescent CdTe nanocrystals (NCs) capped with thioglycolic acid (TGA). The synthesis was performed for 8h at 130°C, was similar to nanocrystal preparation in an aqueous medium, and used safe, low-cost inorganic salts as precursors. After the reaction, the photoluminescence quantum yield of the CdTe NCs (NCIL-130) prepared in EMIDCA was significantly higher than that of the nanocrystals prepared in water (NCw) at 100°C (86% vs. 35%). Moreover, the emission wavelength and particle size of NCIL-130 were smaller than NCw (450nm vs. 540nm and 4.0nm vs. 5.2nm, respectively). The activation of NCIL-130 was successful due to the coordinated action of two ligands, EMIDCA and TGA, in the primary steps of the NC formation pathway. An increase or decrease in the synthesis temperature, to 160°C or 100°C, respectively, was detrimental to the luminescence quality. However, the quenching effect of Hg2+ on the fluorescence signals of the NCIL-130 was distinctively unique, whereas certain interfering ions, such as Pb2+, Fe3+, Co2+, Ni2+, Ag+, and Cu2+, could also quench the emission of the NCw. Based on the Perrin model, the quenching signals of NCw and NCIL-130 were well correlated with the Hg2+ concentrations in the phosphate buffer (pH 7.5, 50mM). In comparison with the NCw, the NCIL-130 had a high tolerance of the interfering ions coexisting with the Hg2+ analyte, high recovery of Hg2+ spiked in the BSA- or FBS-containing medium, and high stability of fluorescence quenching signals between trials and days. The NCIL-130 nanocrystals can potentially be used to develop a probe system for the determination of Hg2+ in physiological samples.