| The quantum dots(QDs),was generally called semiconductor nanocrystalline, with their various potential characteristics such as adjusted size, wide excitation wavelength, narrow emission wavelength, good stability, high quantum yield, and excellent biocompatibility, have been attracting wide interest owing to their various potential applications in biomarkers, tracer, imaging, etc,. The QDs can be prepared in organic phase or in aqueous phase. The traditional organic preparation methods have been more mature, and the prepared QDs have high dispersion, high quantity and high quantum yield. However,the QDs prepared in this method demands rigorous reaction conditions, and have some shortcomings of high cost, high toxicity, and weak biocompatibility. For that reason, here we prepared the QDs in aqueous solution with the advantages of low cost, mild and controllable reaction condition and obligation of environmentalist. We mainly included the following experiment works:(1) Preparation of TGA modified CdSe QDs and optical properties study in low temperature. Here we investigated the effects of reaction temperature, reaction time, the material ratio, pH value and so forth on QDs growth rate and fluorescence properties.The results showed that the QDs prepared in the ice bath have higher quantity and stability. Moreover, through the spectrum analysis we can see that the synthetic CdSe QDs in this condition has520nm emission peak, and the quantum yield can reach14%. Characterization the structure of CdSe QDs by using the fluorescence spectra, transmission electron microscopy and X-ray diffraction. The size of the CdSe QDs is3-10nm. (2) Preparation and characterization of type Ⅱ MPA-CdSe/ZnTe core-shell QDs. As we all know, the preparation of ZnTe in aqueous solution is so difficult that there is little breakthrough. We choosed the MPA as stabilizator, ZnCl2and Te power as precursor materials,initially created a new method of convenient and efficient obtaining type Ⅱ MPA-CdSe/ZnTe core-shell QDs in the water phase. From the experiment, we found that the light efficiency and chemical stability of QDs have significantly increased after coating ZnTe shell. And the optical properties of core-shell QDs will have obvious variation with the different reaction temperature, time, pH and ZnTe shell thickness. In the most optimal synthesis conditions, the prepared water-soluble type ⅡCdSe/ZnTe core-shell semiconductor quantum dot has a wide emission wavelength and high fluorescence optical properties, the fluorescence emission spectrum was continuously adjustable in the range of500-573nm, and the biggest fluorescence quantum yield can reach6.8%. The fluorescence spectrum,transmission electron microscope (TEM), X-ray diffraction (XRD) were performed in order to characterise the prepared QDs. And the results show that the QDs have3.2nm.(3) Preparation of fluorescence coding microsphere with quantum dots and polystyrene. Preparing the quantum dots-polystyrene(PS) microsphere by the swelling method refers that making the PS swell in the organic solvent, That is to say, making fluorescence materials(small organic molecular dyes or quantum dots) swell inside microsphere to form fluorescence microspheres through strong hydrophobic interaction between the surface of particles and the surface of microspheres. Here we adopted the swelling method to embed the QDs in the PS microsphere as the different fluorescence CdSe and CdSe/ZnTe for nucleus, and the synthetic QDs/polymers composite material has good biocompatibility. The optical coding of fluorescence microsphere can be achieved through changing the emission wavelength and luminous intensity of the core QDs. The fluorescence images were obtained using the fluorescence microscope, and we can clearly observe the luminous polystyrene fluorescence microsphere. The prepared QDs-PS coding microsphere has a lot of excellent performance, and will lay a good foundation for the following medical diagnosis and other biological applications. |
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