Study On Hyper Rayleigh Scattering Of Alkanethiol Capped Gold Nanorods

The gold nanorods(GNDs)have various applications in optical sensing,bimolecular imaging,medical diagnosis and tumor therapy,owning to their unique optical properties and good biocompatibility.However,GNDs are less stable and prone to aggregation because of the high specific surface energy.In order to take advantage of GNDs,their surface must be modified and coated.The suitable coating layer can give GNDs more stability as well as new functions.The thiol derivatives coating layer can form tight Au-sulfur coordination bone with GNDs and has high sensitivity in bio-imaging so it has receive a great deal of interest over the last years.Hyper-Rayleigh scattering(HRS)technique is a common method to investigate the characterization of second order nonlinear optical properties of materials.The primary aim of this thesis is to study the effect of alkyl-thiol coating layers of GNRs in a nonlinear optical view by using HRS theory.In this work cetyltrimethyl ammonium bromide(CTAB),dodecanethiol and octadecanethiol coated GNDs were synthesized respectively through silver ion assisted seed-growth method and were studied through Hyper-Rayleigh Scattering(HRS)technology combined with UV-Visible absorption spectroscopy and the Transmission Electron Microscopy(TEM).Additionally,polarized HRS intensity responses from centrosymmetric molecular aggregation were simulated.The results show that CTAB coating layer seems to enhance the hyperpolarizability whereas alkyl-thiol layers in the opposite tend to quench the response.Furthermore,it appears that the length of alkyl chain does not provide any effect on the hyperpolarizability but the alkyl chain plays an important role in preventing aggregation.Both experimental and simulated results show that HRS method is a sensitive way to detect the surface defects and aggregation of nanoparticles.