1. Department of Analytical Chemistry, China Pharmaceutical University, Nanjing 210009, China 2. School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
Abstract：The quantum dots (QDs) synthesized in aqueous solution have more advantages than those synthesized in organic solution, for drugs always act on the biological systems. In addition, the CdTe QDs surface-bound TGA molecules can not only enhance the fluorescence intensity, but also improve the stability of quantum dots, which makes the integrate of quantum dots and the organism easier. The present paper studied on the interaction of CdTe quantum dots, which were synthesized in aqueous solution with pazufloxacin, the forth generation of quinoloines drugs by fluorescence spectrum and absorption spectrum. The results showed that the fluorescence intensity of CdTe quantum dots decreased regularly with increasing concentration of pazufloxacin. No absorption band was observed in the 400-700 nm wavelength range for pazufloxacin, so the quenching effect of pazufloxacin on the fluorescence of CdTe QDs was not due to an inner filter resulting from the absorption of the emission wavelength by pazufloxacin. No obvious change was observed for the CdTe QDs absorption spectra before and after adding pazufloxacin, and a blue-shift or red-shift of the fluorescence emission spectra was also not seen when the concentration of pazufloxacin was changed from 10.0 to 850 μg·mL-1, which also meant that CdTe QDs had not aggregated or become smaller after adding pazufloxacin. And the CdTe QDs, which had a good dispersion characteristic, uniform shape and centralized distribution whether in or out of pazufloxacin solution, were observed by the images of transmission electron microscopy. This indicated that the mechanism of the reaction was likely to be that the changes of surface-bound organic molecules of QDs, the —COOH chemical bond, were induced by pazufloxacin, and the Te-oxygen complex was formed at the Cd surface vacancies. Based on the quenching of the fluorescence of CdTe QDs by pazufloxacin, a rapid, novel and specific method for pazufloxacin determination was proposed. In the optimum conditions, pazufloxacin concentration versus quantum dots fluorescence gave a linear response with an excellent 0.995 4 correlation coefficient, between 10.0 and 850 μg·mL-1. The limit of detection (S/N=3) was 3.254×10－3 μg·mL-1. And the quenching constant could be obtained, which was 2.188×104 L·mol-1. The RSD value about fluorescence quenching of CdTe QDs by 5 groups of 50 μg·mL-1 concentration of pazufloxacin was 0.3%. The contents of pazufloxacin in freeze-dried powder injection and sodium chloride injection were determined by the proposed method and the results agreed with the claimed values. The proposed method is much more convenient, rapid, sensitive and has a much broader linear range than other methods, such as HPLC, HPCE and UV etc. It is hopeful to contribute to the development of the studies of pharmacal imaging and the reaction mechanisms of medicines in vivo further.
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