Surface grafted polymers on metal nanospheres and ligand exchange reactions on metallic nanorods.

摘要

Gold and silver nanoparticles have attracted the interest of researchers due to their unique optical properties. These properties are attributed to localized surface plasmon resonance (LSPR). LSPR results from the collective oscillation of conduction electrons of metals with the incident light and is manifested as strong absorption bands in the visible regions of the electromagnetic spectrum. Due to these unique optical properties, nanoparticles can serve as the basis for new technologies and have been used extensively in variety of applications. Gold nanoparticles are particularly attractive since they are well suited to the human body and can find potential applications in drug delivery and sensing.;Surface modification of gold nanoparticles plays a critical role in determining their function. Nanospheres have the simplest particle geometry for performing modification techniques. On the other hand, nanorods with their anisotropic geometry present morphological advantages. This thesis delves into various surface modification techniques performed on gold nanospheres and discusses the ligand exchange reactions on gold nanorods.;Surface modification of gold nanospheres was carried out using "grafting to" and "grafting from" approaches. Two distinct detection platforms were developed using gold nanoparticles using the "grafting to" technique. Gold nanoparticles were stacked on a glass slide using a thermoresponsive polymer (poly-N-isopropyl acrylamide) as a linker between adjacent gold layers. Aggregation behavior of gold nanoparticles attached to the glass slide was studied under the influence of an external stimulus. The other detection platform comprised of a hybrid material that was synthesized by incorporating gold nanospheres onto biopolymer dextran. The interaction of the hybrid system was tested with bivalent metals such as tin. In another application, thermoresponsive polymer brushes of N-isopropylacrylamide (NIPAAm) were grown on gold nanospheres using Atom Transfer Free Radical Polymerization (ATRP).;To study the ligand exchange reactions on gold nanorods, surface modification of nanorods was systematically investigated; particularly, the adsorption and displacement of the cationic surfactant, cetyltrimethylammonium bromide (CTAB) on model crystalline gold surfaces representing crystal facets on gold nanorods were studied. Adsorption of CTAB from aqueous media onto gold surfaces of different crystal orientations was studied by water contact angle measurements, FT-IR spectroscopy and cyclic voltammetry. Displacement of adsorbed CTAB molecules with various alkanethiols from planar gold surfaces was performed using various incubation times with thiols. The displacement reaction was characterized by various analytical methods.