In this research, CdTe nanocrystals (NCs) of different sizes were synthesized through a chemical precipitation technique and used as the fluorescence probe of Cd ions in the fluorescence turn-on mode. Then, they were combined with various concentrations of Cd2+ ions as well as Na2S2O3 as a source of S. Na2S2O3 was applied to increase the sensing ability of the sensors in the range of 1 to 1000 μM. Different sizes of CdTe NCs from 1.3 to 3 nm and quantum yields from 11 to 19% were applied for the sensing. A sensitive and simple method was proposed for the detection of Cd ions. The morphology and the structure of the CdTe NCs were also investigated by transmission electron microscopy and X-ray diffraction analyses. Using Cd2+ ions and Na2S2O3 leads to the reduction of the surface trap states of the CdTe NCs. The fluorescence intensity of the CdTe NCs was thus increased with Cd2+ ions plus Na2S2O3, but the increase of fluorescence intensity did not occur in the samples without a source of S. Besides, smaller CdTe NCs proved to be more sensitive to Cd2+ in the solution. The reported method improves the possibilityof the selective determination of Cd2+, excluding the tangible influence of potential interfering ions such as Hg2+, Ca2+, Na+, K+, Cu2+, Co2+, Cr2+, and Mg2+. This method provides a simple tool to determine Cd ions in a wide range of Cd2+ concentrations.
