Surface Modification and Self-Assembly of Gold Nanostructures
Doctor of Philosophy
This thesis describes self-assembly and surface modification of gold nanoparticles and nanorods. It begins with an efficient surface functionalization of gold nanoparticles with a liquid crystalline ligand that structurally resembles liquid crystal 5CB. Functionalized gold nanoparticles show increased solubility in liquid crystal compared to their alkanethiolated analogues. Surface modification technique was also applied to detoxify gold nanorods for biological applications. The process involves a ligand exchange step where cytotoxic CT AB bilayer of gold nanorods was replaced by thiolated CTAB. Covalent nature of gold-sulfur bond allows for the complete removal of CTAB via centrifugation. Functionalized gold nanorods are virtually non-toxic and they show efficient cellular uptake by cancer cells. This thesis also describes self-assembly of gold nanoparticles and nanorods into well organized colloidal crystals. Slow precipitation technique was implemented to prepare three dimensional colloidal crystals of alkanethiolated gold nanoparticles. Colloidal crystals of gold nanorods were prepared by evaporation induced self -assembly technique. Additionally, orientation of nanorods in a colloidal crystal can be altered from side-on to tip-on by controlling the hydrophobicity of the underlying substrate. Our investigation showed that the presence of excess surfactant (CTAB) strongly influences the crystallization process. The shape and size of self assembled structures were also controlled by creating patterned hydrophobic and hydrophilic areas on a substrate. A variety of self assembled structures can be prepared by controlling the dimensions of the patterns. Finally, an efficient synthesis of hybrid cadmium sulfide-gold nanowires was described.
Applied sciences; Chemistry