Quantum dot-based "turn-on" fluorescent probe for detection of zinc and cadmium ions in aqueous media

Health or environmental issue caused by abnormal level of metal ions like Zn(2+) or Cd(2+) is a worldwide concern. Developing an inexpensive and facile detection method for Zn(2+) and Cd(2+) is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn(2+) and Cd(2+) in aqueous media was reported. The proposed probe worked in fluorescence "turn-on" mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S(2-)). The presence of Zn(2+) (or Cd(2+)) can "turn-on" the weak fluorescence of QDs quenched by S(2-) due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn(2+) (or Cd(2+)) could be obtained in the range from 1.6 to 35 μM (1.3-25 μM for Cd(2+)). The limit of detection (LOD) for Zn(2+) and Cd(2+) were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn(2+) and Cd(2+) over other metal ions and was successfully used in the detection of Zn(2+) or Cd(2+) in real water samples.