Thioglycerol-functionalized CdSe quantum dots detecting cadmium ions

Water-soluble CdSe quantum dots (QDs) were synthesized using thioglycerol (TG) as the surface capping agent through a one-step process at low temperature T (100 °C). The CdSe quantum dots were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, UV-visible absorption and fluorescence spectroscopies. These measurements revealed that the TG-capped CdSe QDs possess a high crystalline quality with an average diameter in the range 2.5-2.8 nm and exhibit particular optical properties. The UV-visible absorption of CdSe QDs is enhanced by the addition of cadmium ions, with a simultaneous shift of the edge band (400 nm), while seventeen other tested metal cations have no effect on the absorption of QDs. Moreover, the binding of Cd²⁺ ions induces a quenching of the fluorescence emission of TG-CdSe QDs. At particular absorption wavelengths, the response is linearly proportional to the cadmium ions concentration ranging from 1.0 to 22 μM with a detection limit of 0.32 μM (37 μg L^-1). Based on these optical properties, the TG-CdSe QDs could be used as a highly selective probe for the detection of Cd²⁺ ions in aqueous solutions, a species highly toxic for cells.