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No description available.

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The ability to grow materials in the nanometric size regime with controlled shape and size provide a fundamental synthetic challenge, while allowing for evaluation of such unique nanostructures in multiple applications. In this dissertation, colloidal sodium lanthanide fluoride (NaLnF4) nanocrystals are described with an overall emphasis on i) size control, ii) surface chemistry related towards their applications as nano-bioprobes, and iii) the synthesis and fundamental aspects of epitaxial layer growth generally referred as core-shell nanocrystals. Chapter 1 provides a brief overview on the basic aspects of colloidal nanocrystals. In Chapter 2, synthesis and surface modification of colloidal sodium lanthanide fluoride nanocrystals, epitaxial growth, and their applications in optical and magnetic resonance imaging is reviewed. Chapter 3 describes a phase transfer protocol utilizing polyvinylpyrrolidone and subsequent silica coating of initially hydrophobic upconverting nanocrystals. This protocol is extended in Chapter 4 using end-group functionalized polyvinylpyrrolidone and demonstrates tunability of surface charge and functional groups on upconverting nanocrystals for targeted labeling of human prostate cancer cells. The synthesis of size-tunable NaGdF4 nanocrystals below 10 nm is described in Chapter 5. These nanocrystals are evaluated for their efficacy in magnetic resonance imaging (MRI), and a fundamental insight into the effect of surface gadolinium ions in T1 MRI contrast enhancement is presented. Chapter 6 demonstrates the synthesis of tunable, epitaxial layers on upconverting (core) nanocrystals. A novel synthetic strategy is demonstrated, by deliberate defocusing and self-focusing of differently sized nanocrystals driven by the common physical phenomenon of Ostwald ripening. Utilizing the contraction of lanthanide ions along the series, a fundamental investigation on the effect of compressive/tensile strain epitaxial layer growth is presented in Chapter 7. The fundamental rule of minimal lattice mismatch for epitaxial growth takes into account only the magnitude of mismatch and not the sign of mismatch caused by a compressive/tensile strained layer. A strong asymmetric effect between the compressive/tensile layer growth given the same magnitude of lattice mismatch is observed, demonstrating the necessity of including the sign of mismatch to generate isotropic (conformal)/ pseudomorphic (coherent) epitaxial growth. Finally, in Chapter 8 conclusions and possible future work are discussed. / Graduate / 0494

Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. In this work, a combination of TEM (transmission electron microscopy), XRD (X-ray Powder Diffractometry), EDS (Energy disperse X-ray spectroscopy), SQUID (Superconducting Quantum Interference Device), TGA (Thermograviometric analysis), UV-visible absorption spectroscopy and Faraday rotation were employed to characterize the morphology, structure, composition and magnetic properties of the products. HRTEM images show clear core-shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Au-coated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And all the above characterizations show that in this sample, there are no Fe oxides inside the particle.

Colloidosomes are microcapsules whose shells consist of colloid particles, which are coagulated by a stabiliser or fused by sintering. In recent years, they have attracted considerable attention because of their potential applications in a range of industries, such as food, bioreactors and medicine. However, traditional particulate polymer shell colloidosomes leak low molecular weight encapsulated materials due to their intrinsic shell permeability, and this problem will limit their applications in pharmaceutical industries. In this thesis, we report aqueous core colloidosomes coated with a silver or gold shell, which make the capsules impermeable. The shells can be ruptured using ultrasound. The silver shells are prepared by making an aqueous core capsule with a particulate polymer shell and then adding AgNO3, surfactant and L-ascorbic acid to form a second shell. The gold coated colloidosomes are prepared by making an aqueous core capsule with a particulate polymer shell and then adding HAuCl4, surfactant and L-ascorbic acid. We propose to use the metal coated capsules as drug carriers to load an anticancer drug, doxorubicin. After triggering by ultrasound, encapsulated drug, broken fragments and possibly some drug attached on the surface of the capsules may all kill cancer cells. For silver coated colloidosomes, at 10 capsules/cell, they have a low cytotoxicity, showing a cell viability of more than 90% during the first 24 h and more than 60% after 72 h. Increasing the number of capsules, the cytotoxicity of the silver shells increases heavily. Compared with silver ones, the gold shells show less toxicity to cells. We also used the capsules to load an antibiotic kanamycin and triggered to release the drug and kill E.coli. In addition, we set up a targeting model by modifying the colloidosomes using 4,4'-dithiodibutyric acid and attaching them with proteins - rabbit Immunoglobulin G (IgG). Label-free Surface Plasmon Resonance biosensor was used to test the specific targeting of the functional silver or gold shells with rabbit antigen. The results demonstrate that a new type of functional metal coated colloidosome with non-permeability, ultrasound sensitivity and immunoassay targeting could be applied to many medical applications.

Thesis (M. Phil.)--University of Hong Kong, 1974.

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No description available.