The Detection Of Metal Ions Based On The Fluorescence Quenching Of Quantum Dots

Quantum dot is a kind of semiconductor material,which the three dimensions are in nanometers, and the particle size in 1-100 nm.The unique features it owned are based on quantum effects. The size confinement will cause size effects, quantum confinement effects, macroscopic quantum tunneling effect and surface effects when the particle size to nanometer size. Compared to conventional mail dye,the optical properties of quantum dots has some advantages as follows: the emission spectrum can be controlled by particle size, good optical stability, wide excitation spectrum and narrow emission spectrum, symmetric emission spectrum, good biocompatible.In this paper, the main contents are summarized as follows:（1） Based on the quenching effect of the Cu²⁺ to the fluorescence of the CdS quantum dots, the analyzing method of the micro-quantity Cu²⁺ in water was established. The result shows that the relationship between the ΔF/F and the Cu²⁺ concentration was linearity according to the Stern-Volmer equation, while the Cu²⁺ concentrations were between the 1.00×10-5 and 3.00×10-4 mol·L-1. The linear correlation coefficient was 0.9952. The recovery of the method was between 95.5 % and 118.5 %, the RSD was 3.8 %, and the detection limit was 5.90×10-6 mol·L-1.The quenching mechanism of the fluorescence was discussed. The interferences of some materials were investigated, the result showed that the fluorescence of the quantum dots were quenched by some materials but enhanced by others. The fluorescence intensity of the CdS quantum dots had different corresponding to the different metal ions. The proper masking agents could be used to eliminate the strong interference of some ions.（2）Based on the quenching effect of the Co²⁺ to the fluorescence of the CdS quantum dots, the analyzing method of the micro-quantity Co²⁺ in the water was established. We studied the effects of pH to the fluorescence of the CdS quantum dots in the potassium dihydrogen phosphate and sodium borate buffer system. The result shows the analysis plays the best when the pH=7, so we chose the neutral environment of pH=7. The result also shows that the relationship between the ΔF/F and the Co²⁺ concentration was linearity according to the Stern-Volmer equation, while the Co²⁺ concentrations were between the 1.00×10-5 and 2.50×10-4 mol·L-1. The linear correlation coefficient was 0.9969. The detection limit of the method was 1.30×10-6 mol·L-1, and the recovery is between 94.5 % and 105.8 %.We study the interference of some metal irons and compounds to this method, the proper masking agents could be used to eliminate the strong interference of some ions. This method based on the quenching effect of the Cu²⁺ to the fluorescence of the CdS quantum dots is faster, more accurate, and easier, compared to the traditional method. And it shows very high selectivity and wide linear range, the result is satisfactory.