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Due to their excellent fluorescence property, quantum dots, as labels for biological tagging, have been used widely in the research of biomedicine nowadays. With the development of nano-technic, biology and testing technology, and the intensive research of quantum dots, we believe that multifunctional quantum dots would be obtained in the near future for biomedical application, with advantages such as good biocompatibility, high specificity, low biological toxicity and stable properties, which means the new era of quantum dots markers. In this paper, by direct aqueous synthetic method at low temperature, CdS quantum dots with excellent fluorescence property were obtained. This paper also discussed that the preparation conditions influence on crystal structures, morphologies, absorption spectrum and fluorescence properties of CdS nanocrystals, and provided the necessary theoretical basis for the development of CdS quantum dots as biological markers.First, yellow-green CdS quantum dots were successfully prepared at 300 K, using CdCl2 and TAA as the precursors, and trisodium citrate served both as a stabilizer to disperse QDs and a kind of catalyst of the reaction, the water-soluble nanoparticles were characterized by means of XRD, HRTEM and energy spectra on their crystal structures, morphologies, sizes and components. The results showed that the products had homogeneous size and good dispersion. CdS quantum dots with the size of 2.5~5.0 nm were obtained by changing reagent concentration, stabilizer concentration and reaction time.Second, in this experiment, the optical property of as-synthesized CdS quantum dots was characterized by UV-Vis absorption spectrum and photoluminescence spectrum. The results indicated that CdS nanoparticles synthesized showed quantum size effects with the blue shift of their absorption spectra, and they own small range of particle size distribution and excellent fluorescence property with the evidence of narrow-band emission in Photoluminescence spectra. In this part, synthesis conditions were changed to study their effect on the optical property of quantum dots. The conditions include reagent concentration, stabilizer concentration, reagent molar ratio, reaction time and regulating the pH of solution, and the mechanisms are discussed.
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