An "off-on" fluorescent nanosensor for the detection of cadmium ions based on APDC-etched CdTe/CdS/SiO₂ quantum dots

In this study, we have developed a novel fluorescent "OFF-ON" quantum dots (QDs) sensor based on CdTe/CdS/SiO₂ cores. Ammonium pyrrolidine dithiocarbamate (APDC), ethylenediamine tetraacetic acid (EDTA), and 1,10-phenanthroline (Phen) served as potential chemical etchants. Among these three etchants, APDC exhibited the most pronounced quenching effect (94.06%). The APDC-etched CdTe/CdS/SiO₂ QDs demonstrated excellent optical properties: the fluorescence of the APDC-etched CdTe/CdS/SiO₂ QDs system (excitation wavelength: 365 nm and emission wavelength: 622 nm) was significantly and selectively restored upon the addition of cadmium ions (Cd²⁺) (89.22%), compared to 15 other metal ions. The linear response of the APDC-etched CdTe/CdS/SiO₂ QDs was observed within the cadmium ion (Cd²⁺) concentration ranges of 0-20 μmol L^-1 and 20-160 μmol L^-1 under optimized conditions (APDC: 300 μmol L^-1, pH: 7.0, reaction time: 10 min). The detection limit (LOD) of the APDC-etched CdTe/CdS/SiO₂ QDs for Cd²⁺ was 0.3451 μmol L^-1 in the range of 0-20 μmol L^-1. The LOD achieved by the QDs in this study surpasses that of the majority of previously reported nanomaterials. The feasibility of using APDC-etched CdTe/CdS/SiO₂ QDs for Cd²⁺ detection in seawater, freshwater, and milk samples was verified, with average recoveries of 95.27%-110.68%, 92%-106.47%, and 90.73%-111.60%, respectively, demonstrating satisfactory analytical precision (RSD ≤ 8.26).