Label-free fluorescence platform based on SiO₂-coated CdTeS quantum dots for trace analysis of Ag⁺ in environmental water

In this study, a core-shell structural nano-composite material, namely CdTeS@SiO₂, is synthesized by a simple silanization of Te-doped CdS quantum dots (CdTeS QDs). Through SiO₂ capping, CdTeS QDs not only improve the fluorescence performance effectively, but also greatly enhance the anti-interference ability in the environment. Based on its excellent optical properties, a novel fluorescence sensor is constructed for the ultramicro detection of Ag⁺. The fluorescence of CdTeS@SiO₂ is strongly quenched in the presence of Ag⁺ and shows good linearity in the range of 0.005-5.0 μmol L^-1 with a detection limit as low as 1.6 nmol L^-1. This is mainly due to its unique quenching mechanism: Ag⁺ destroys the spherical structure of SiO₂ and promotes the formation of non-radiative electron-hole pairs through electron transfer, leading to fluorescence quenching. At the same time, it competes with Cd for Te, S and MPA on the CdTeS surface, forming Ag-Te, Ag-S and Ag-MPA complexes attached to the CdTeS surface leading to wavelength red-shift. The feasibility of the proposed sensor is demonstrated through spiking experiments, which confirmed the potential value of the constructed fluorescence probe for real-world applications in detecting Ag⁺ in environmental water.