Gold nanorod surface functionalization: construction of dynamic surfaces and heterogeneous silica coating

Gold nanorods (GNRs) have been investigated due to their unique surface plasmon resonances (SPR) that are tunable in wavelength according to nanoparticle shape. The collective oscillation of the electrons in the GNRs excited by incoming light leads to enhanced electromagnetic fields near the gold surface, and thus can enhance the photophysical properties of nearby molecules. It has been demonstrated that enhancement of optical properties such as fluorescence and Raman scattering are distance-dependent from the metal surface, which makes the control of distance between the optical probe and gold surface of crucial importance. Meanwhile, researchers have also demonstrated that the electromagnetic fields are anisotropic, with higher fields located at the end of the GNRs upon excitation into the long-axis SPR mode. Thus, controlling the position of molecules on GNR surfaces is a major challenge in the field. The first aim of this thesis is to build up dynamic surface coatings on GNRs that change their thickness and reversibly responsible to specific outside stimuli. Poly (N-isopropylacrylamide) (PNIPAM), with lower critical solution temperature around 32°C in water, was chosen as the thermal responsive coating on GNRs. The dynamic surface on GNRs could be achieved by a simple graft-to functionalization step. Plasmon enhanced fluorescence and surface enhanced Raman were both investigated to report on the dynamic distance change, and we found reversible enhancement of the Raman signals of attached bipyridine ethylene (BPE) molecules in solution. We also investigated polymer graft-from the GNR surface in situ so that the grafting density and polymer composition can be fine-tuned for further application. The second part of this thesis focuses on the heterogeneous silica coating of GNRs. A robust method has been developed for synthesis of side-specific silica coating and end-specific silica coating on GNRs with average rod diameter of around 15. The mechanism of the heterogeneous synthesis is investigated and GNRs with different aspect ratios was tested to illuminate the growth mechanism