Controllable Synthesis And Biological Effects Of Water-soluble Quantum Dots

Currently, there are many functional nanomaterials used in biomedicine, semiconductor fluorescent quantum dots (QDs) is one of the most popular nanomaterials. As the quantum size effect and dielectric confinement effects, QDs have unique optical properties, which making QDs have tremendous potential not only in the optical field but also in the biomedical field. In recent years, the biological effects and toxicological studies of QDs and other nanomaterials have attracted much attention of the world. Results of various studies to date show that the toxicity of QDs has some connection with the particle size, concentration, surface modification group, aggregation, the release of heavy metals ion Cd2+, surface charge, cell endocytosis, oxidation of reactive oxygen generation and reactive oxygen species-mediated oxidative stress and other factors. Until now, all studies are limited to a certain point of view of its toxicity. No one has systematically investigated and clarified the biological effects mechanisms of QDs from ecological environment, individual (embryo), cells and biological macromolecules.This thesis is focused on developing novel and facile synthesis approach of quantum dots, and comprehensively comparing the toxic effect of CdSe and CdTe QDs on embryonic development (zebra fish, cooperation), protozoa (Tetrahymena) metabolism, fungal and bacterial metabolism, and activity of biological macromolecules (serum protein and enzyme), then proposing a possible mechanism of action.This thesis consists of six chaptersChapter 1:This chapter introduced a more comprehensive overview of quantum dots, progress in synthesis, surface chemical modification, application in biomedical areas and toxicity. Chapter 2:We used organic coordinating solvent methods to prepare high-quality CdSe core and CdSe/ZnS core/shell QDs, and then modified them with hydrophilic molecules and biological macromolecules. By taking NAC as the stabilizers, we synthesized high-quality CdTe core QDs rapidly and both excellent optical performance and biocompatibility of the CdTe/CdS/ZnS core/shell/shell QDs through the epitaxial growth of CdS and ZnS shell on the surface of CdTe core QDs.Chapter 3:By using microcalorimetry, we studied the biological activity of Tetrahymena thermophila BF5 affected by CdSe core and CdSe/ZnS core/shell QDs, and the corresponding half-inhibitory concentration is 1.14×10-6 mol L-1 and 1.18×10-6 mol L-1, respectively. Results show that the growth of ZnS shell can improve the stability, and effectively reduce its action on the growth process of Tetrahymena thermophila BF5. When the surface is modifed with biological molecules and PEG, QDs have much better biocompatibility. Furthermore, by using inverted fluorescence microscopy, we found that the toxicity take place within the cell. The results show that QDs is highly cytotoxic, and the possible mechanism could be related to its unique physical and chemical properties and release of toxic ions.Chapter 4:By using microcalorimetry, we studied the biological activity of E. coli and S. aureus affected by CdSe core and CdSe/ZnS core/shell QDs and the biological activity of the two types of bacteria (E. coli and S. aureus) and two fungi (S. cerevisiae and C. albicans) affected by CdSe/ZnS QDs with different types of surface modification (MAA and CA). The results showed that the ZnS shell can improve the stability, and effectively reduce the exposure of toxic metal ions to avoid the cytotoxicity. At the same conditions, Gram-negative bacteria is more sensitive to QDs, according to the obvious dose effect between growth rate constants and the concentrations of QDs, while Gram-positive bacteria do not have this effect. Under experimental conditions, CA-QDs with a positive charge have higher cytotoxicity, because they can be easily adsorbed to the cell surface through electrostatic interaction, while MAA-QDs with a negative charge are more difficult to interact with the cell.Chapter 5:We systematically investigated the interaction between CdSe/ZnS QDs with different surface modification (MAA and CA) and four different sizes of MPA-CdTe QDs and serum albumins under the approximatively physiological conditions. The possible mechanism of action arriving from surface modification and particle size of QDs is proposed at the same time.Chapter 6:We successfully synthesized monodisperse mercaptopropionic acid (MPA) modified CdTe core QDs. By using fluorescence spectroscopy, we investigated the interaction between MPA-CdTe and four kinds of enzymes (papain, pepsin, trypsin and lysozyme) under the approximatively physiological conditions. The fluorescence quenching mechanisms were discussed; the binding constants, thermodynamic parameters, binding distance, and the binding mode were calculated and discussed. In addition, three-dimensional fluorescence and circular dichroism spectroscopy methods were used to investigate the secondary structure change of enzymes affected by QDs.