Synthesis And Properties Of Novel CdSe Nanocrystals

Generally, nanocrystals as luminescent probe for biological labeling should be water-soluble, biocompatible and covalently coupled to biomolecules. Current methods are mainly focusing on the transfer of the nanocrystals synthesized in organic phase from hydrophobic surface to hydrophilic and biocompatible surface. The methods to prepare nanocrystals in aqueous medium using thiols as stabilizing agents were also reported. However, the biocompatibility of the nanocrystals is not well enough. In this thesis, a new method to synthesize required CdSe nanocrystals in aqueous solution using polyethyleneglycol derivatives as stabilizing agents was developed. Furthermore, preparation of hybrid polymer using above prepared functional CdSe nanocrystal assembly as building blocks was also investigated to satisfy various applications. The detail is as follows:(1) We designed and synthesized functional organic molecules of mercapto-polyethyleneglycol, polyethyleneglycol terminated with mercapto and ethenyl groups, etc. These functional organic molecules were used as stabilizing agents for synthesis of CdSe nanocrystals. ¹H-NMR, mass spectrum, elemental analysis, etc. were used to characterize the functional organic molecules.(2) Synthesis of CdSe nanocrystals in aqueous medium using mercaptoacetic acid as stabilizing agents was investigated in detail. Reaction condition such as nucleation temperature, charging ratio of CdCl₂/Na₂SSeO₃/HSCH₂COOH, ripening time and so on, was optimized. Preparation of powder sample of CdSe nanocrystals was also investigated and got succeeded. The work of this part laid the foundation for synthesizing novel functional CdSe nanocrystals.(3) Under the optimized condition above, we got succeeded in synthesis of series CdSe nanocrystals with different size in aqueous solution by using mercapto polyethyleneglycol as surfactant. We characterized them by X-ray diffraction (XRD), transmission electronic microscope (TEM), Uv-vis absorption spectrum, and fluorescence spectrum (PL), etc. The experimental results showed that the CdSe nanocrystals were uniform in radius, had good crystal structure and good property in fluorescence.We also got succeeded in synthesis of CdSe nanocrystals in aqueous solution by using mercapto polyethyleneglycol and 11 -mercaptoundecanoic acid as stabilizing agents. By adjusting the charging ratio of the two surfactants, we synthesized CdSe nanocrystals modified with different functional organic molecules to satisfy various applications. The hydroxyl and the carboxyl groups on the surface of CdSe nanocrystals make them possible to couple with biomolecules. The structure units of polyethyleneglycol on the surface of CdSe nanocrystals make them water-soluble, biocompatible. We studied the structure, size and distribution of the CdSe nanocrystals by TEM, Uv-vis absorption spectrum, etc. We defined the ratio of the hydroxyl and the carboxyl groups on the surface of CdSe nanocrystals by NMR and IR spectra. Fluorescence spectrum showed that CdSe nanocrystals had good fluorescence.(4) Under the optimized condition above, CdSe nanocrystals modified with mercapto polyethyleneglycol and mercapto polyethyleneglycol with ethenyl groups were prepared. We defined the ratio of the hydroxyl and the carboxyl groups on the surface of CdSe nanocrystals by NMR spectrum. We investigated the free fadical homopolymerization of CdSe nanocrystal assembly modified with ethylene groups and succeeded in preparation of molecular hybrid polymers with CdSe nanocrystal assembly as building blocks. We characterized the structure, size and distribution of the CdSe nanocrystals and the polymers by TEM, Uv-vis absorption spectrum, etc. We studied the luminescence of the CdSe nanocrystals and the polymers by fluorescence spectrum. The experimental results showed that the CdSe nanocrystal assembly and the molecular hybrid polymer are good in dispersity and in fluorescence.In summary, three kinds of novel functional CdSe nanocrystals and a molecular hybrid polymer using the CdSe nanocrystal assembly as building blocks were prepared. They show good solubility in water and excellent photoluminescence suggesting their potential application in bio-labeling.