Functionalized gold nanostructures with well-defined geometry and controlled optical properties can potentially play an important role in healthcare applications such as biosensing, photocatalysis, drug delivery, photothermal therapy and imaging due to their unique properties. This thesis aims to develop a novel Au nanostructure for healthcare applications, using an effective synthesis protocol in order to produce a suitable Au nanostructure with NIR absorption, high thermal stability and low toxicity. Well-controlled, reproducible Au nanostructures with NIR absorption spectra, including gold nanoparticles (NPs), nanorods (NRs), nanobipyramids (NBPs) and nanotriangles (NTs) have been synthesised using a wet-chemical synthesis approach and characterized using dynamic light scattering and transmission electron microscopy.
The optical and plasmonic properties of the Au nanostructures were investigated using uv-vis spectroscopy, finite element modelling (FEM) and STEM/low-loss EELS analysis was employed. EELS results exhibited good agreement with uv-vis spectra and FEM modeling and revealed the size- and shape-dependent plasmonic properties and showed that NIR absorption can be altered by increasing the curvature of particles.
The thermal stability of Au nanostructures, which is important for photothermal therapy applications, was investigated using in-situ TEM heating. It was found that the thermal stability of Au nanostructures decreased in the order : AuNPs > AuNTs > AuNBPs > AuNRs. The proposed useful temperature ranges whereby heating does not significantly affect the optical properties were up to 100ºC, 200ºC, 800ºC, for CTAB-capped AuNRs, CTAB-capped AuNBPs and CTAC-stabilized AuNTs, respectively. The thermal stability of particles was increased by surface functionalization of the NPs from a CTAB coating, through a PSS coating and finally to a silica coating. Thermal deformation arose from curvature-driven surface diffusion.
Finally, the biocompatibility of Au nanostructures, in terms of the effect of size, morphology, and surface coating, was investigated by their electrochemical interaction with a model membrane based on DOPC on an Hg/Pt electrode. Only smaller Au nanostructures with a diameter of ca. 20 nm exhibited a significant interaction. However, the effect of the surface coating was found to be a more significant effect with the order of interaction with the model membrane ranging from CTAB > PSS > CTAC > citrate coated Au nanostructures.
Thus overall, potential biocompatible candidates for healthcare applications are proposed to be citrate-, PSS- or silica-coated gold nanostructures with NIR absorption and dimensions larger than approximately 20-25 nm.
