An ′On-off-on′ Fluorescence Sensor Based on CdSe Quantum Dots for the Selective Detection of Cd2+

Graphical An “on-off-on” nanoprobe for detecting Cd 2+ was developed using CdSe QDs. Based on the formation of CdSe/CdS QDs, Cd 2+ could restore the fluorescence of CdSe QDs quenched by S 2− . The fluorescence increased with increasing concentration of Cd 2+ in the range of 0.2–9 μM with low detection limit of 27 nM. In this work, an “on-off-on” nanoprobe for specific detection of Cd 2+ was constructed using N -acetyl- l -cysteine (NAC)-modified CdSe quantum dots (QDs). The prepared CdSe QDs exhibit characteristic green fluorescence. The adsorbed S 2− on the surface of CdSe QDs leads to dangling bonds and causes the fluorescence quenching of QDs, where the fluorescence of the system turns “off“. When Cd 2+ exists, it can react with the adsorbed S 2− to form CdS shell, resulting in the fluorescence enhancement of CdSe QDs, where the fluorescence of the system turns “on”. Due to the similar lattice structure between CdSe and CdS, CdSe/CdS can be produced by shell deposition, while self-nucleation of metal sulfide is observed in the presence of other metal ions. Thus, the developed nanoprobe shows high selectivity for Cd 2+ . Under the optimum sensing conditions, the fluorescence sensing signal of CdSe QDs depends linearly on the Cd 2+ in the range of 0.2–9 μM. The limit of detection (LOD) and limit of quantification (LOQ) of this nanoprobe is 27 nM and 90 nM, respectively. Furthermore, the proposed nanoprobe can monitor Cd 2+ in drinking water with a recovery rate between 95.82 % and 102.00 %, indicating its good practicability and applicability for real sample analysis.