Synthesis, Characterization Of Telluride Quantum Dots And Its Application In Biological Labeling

In recent years, quantum dots (QDs) have been widely investigated as a class of luminescent materials. When their size is comparable to the size of Bohr diameter for excitation, they exhibit special physical and chemical properties which include the quantum size effects, dielectric confinement effects, surface effects, macroscopic quantum tunneling effects and so on. And the above effects produce special optical properties for semiconductor quantum dots. So the quantum dots with these special optical characteristics applied in the biological, analytical, material, immune physical and quarantine applications have become a wide research focus. Compared to conventional organic dyes, QDs possess many advantages such as narrower emission spectra, tunable maximum emission wavelength with changeable sizes and compositions, photostability, high brightness, long fluorescence lifetime and biocompatibility, which have been successfully used as fluorescent probe or sensor in the imaging of biological samples and cells.Here, my research is mainly concentrated on the synthesis of CdTe QDs in the water phase and their biological labeling applications. The mainly research achievements are as follows:First, water-soluble CdTe QDs were synthesized with TGA or GSH as a ligand with a facile one-pot method. XRD, HRTEM, DLS, UV-vis absorption and photoluminescence spectra were utilized to characterize the as-synthesized QDs. The results show that the facile one-pot method can be used to prepare high luminescent(the quantum yield as high as 80%), cubic (Zinc blende) CdTe QDs, without the protection of inert gases. The size of CdTe QDs is lower than 5nm, but it increases gradually with the reacting time, which leads to the red shift of the emission and absorption peaks. Furthermore, we found that the ratio of GSH to Cd2+ played a negligible role in the enhancement of quantum yields. The as-prepared CdTe QDs are stable enough at room temperature for at least six months.Second, microwave-assisted method was widely focused on the synthesis of CdTe nanocrystal materials because of its advantage of high heating rate, energy saving and volume heating. Instead of traditional oil bath heating, the microwave-assisted method was used to acquire high quality thiol-capped CdTe quantum dots in aqueous phase in a relatively short time. The size of CdTe QDs also increases gradually with reacting time, and their emission and absorption peaks occur the red shift. However, the red shift decreases with the reacting time.Third, using one-pot method synthesized CdTe QDs as precursor, we prepared HgCdTe QDs by the partial substitution of Cd with Hg ions. Furthermore, we studied element composition ratios in this ternary system and the relationship between ratios and fluorescence spectra. The experimental results indicate that with the increase of Hg amount added the band gap of as-formed HgCdTe QDs narrowed and the wavelength of emitted light at excitation red shifted. The forbidden-band widths between CdTe and HgTe band gaps can be obtained through changing Hg amount in HgCdTe QDs, and therefore, the emission wavelength tuning is finally realized.Fourth, the as-prepared CdTe quantum dots can be used as biological labeling to label cells. After conjugation of CdTe quantum dots with biotin, the biotin-GSH-CdTe QDs probes were used to label the mouse fibroblast cells. The fluorescence images of stained cells show that they still remain very strong fluorescence after dilution, and the experimental results also indicate that the quantum yield of as-synthesized CdTe QDs is very high. It is noteworthy that the high quantum yield is the basics of biological imaging.