Preparation and Applications of Functionalized Quantum Dots and Mesoporous Silica Nanoparticles

This thesis reports the preparation and characterization of a series of cadmium telluride (CdTe) quantum dots (QDs), and the use of these nanoparticles as highly emissive fluorescent probes and catalyzer for photodegradation of pollutants. In addition, functionalized mesoporous silica nanoparticles (MSN) are also described, including their preparation and applications in photodynamic therapy of cancer cells.;Chapter 1 presents an overview of QDs and MSN, including the general preparation procedure, properties, and applications. Special emphasis is placed on those systems conjugated with photo sensitizers.;Chapter 2 describes the preparation, spectroscopic characteristics, and photophysical properties of three CdTe QDs, which emit at 555, 600, and 646 nm. Their conjugation with two silicon(IV) phthalocyanines (SiPcs) is also reported. Upon linking to the QDs, the SiPcs show a higher photostability and efficiency in generating singlet oxygen. The efficiency can be optimized by changing the size of the QDs. The use of these conjugates as photo sensitizers for degradation of 2,4,6-trichlorophenol, which is a major pollutant in paper industry, has also been investigated. The degradation efficiency as monitored by HPLC is significant higher for the conjugates compared with that ofQDs and SiPcs alone.;Chapter 3 reports a novel hybrid approach to prepare highly luminescent CdTelzinc sulfide (ZnS) core/shell QDs. Firstly, the water-soluble CdTe cores are prepared in aqueous media using thioglycolic acid as a surface-modifying agent. Then through ligand exchange, the terminal thioglycolic acid groups are replaced by hexadecanethiol molecules, which allow the QDs to be soluble in organic solvents such as toluene. Lastly, a ZnS shell layer is coated on each CdTe core using zinc(II) diethyldithiocarbamate (Zn(Et2NCS 2)2) as a single-molecular ZnS source to form CdTe/ZnS core-shell nanocrystals. The CdTe/ZnS core-shell structure has been confirmed by X-ray powder diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The hydrophobic hexadecanethiol-coated CdTe/ZnS QDs can also be transferred into aqueous media by using the surfactant cetyltriethylammnonium bromide (CTAB). The resulting CTAB-modified CdTe/ZnS QDs are potentially useful for bioimaging.;Chapter 4 reports an improved procedure for the preparation of highly emissive CdTe QDs. The use of a mixture of ammonia and sodium hydroxide instead of the traditional sodium hydroxide to adjust the pH of the reaction media can lead to great enhancement of the photo-luminescent quantum yield of the QDs. While these QDs can be taken up by human colon adenocarcinoma HT29 cells, they show a cytotoxicity. To circumvent this problem, nontoxic silica has been coated on the surface of CdTe nanocrystals to form highly luminescent, nontoxic, and biocompatible CdTe/SiO2 core/shell nanoparticles which can be applied in biological imaging.;Chapter 5 describes the preparation, photophysical properties, and photodynamic activity of phthalocyanine-encapsulated MSN. In this study, MSN have been used as a carrier for two zinc (II) phthalocyanines (ZnPc 1 and ZnPc 2). The silica framework prevents photo degradation of the phthalocyanines. MSN-phthalocyanine composites show a very high photocytotoxicity toward HT29 cells. These functionalized MSN are also biocompatible showing a great potential as a photosensitizing system for photodynamic therapy.;An extension of this study is reported in Chapter 6. We have modified the surface of the phthalocyanine-entrapped MSN with folic acid groups via the click chemistry with a view to enhancing the active targeting property of this photosensitizing system. The photophysical properties of these multifunctional MSN have been examined.