Engineering gold nanorods for photothermal application

At the moment, cancer therapies involve harmful side effects on patients. Therefore, it is necessary to create safer cancer treatment strategies that can significantly enhance treatment experience. Using near-infrared-absorbent gold nanorods (AuNRs), which have the ideal optical and thermal properties to be used in methods like photothermal therapy, is one way to accomplish this goal. However, the challenges associated to using AuNRs such as the CTAB toxicity, instability under pulsed laser irradiation need to be met. This thesis aims to develop AuNRs in order to make them biocompatible, thermally stable, well-controlled, reproducible and efficient in NIR absorption for effective photothermal applications. In this thesis, this is discussed in three main areas: Firstly, the reduction of the toxicity of CTAB bilayer of bare CTAB@AuNRs through a direct coating method with the inorganic silica shell. Followed by different techniques to confirm the silica coating, such as UV-Vis spectroscopy, Zeta potential, TEM, and EDX elemental mapping. The In-situ TEM heating study showed that the silica shells enhanced the thermal stability of AuNRs, with maintaining their rod shape and protected them from turning into nanospheres even up to 1200 °C. Secondly, the surface of the silica coated-AuNRs were functionalised with DPPC + DSPE-PEG2000 phospholipids to enhance their colloidal stability and biocompability in vitro tests in human colorectal cancer cell lines such as SW620 and HT29. Thirdly, the influence of the silica coating on AuNRs reshaping behaviour under nanosecond pulsed laser irradiation as a function of irradiation time, fluence, and porosity degree was explored and analysed by UV-Vis spectroscopy and Transmission electron microscopic (TEM). In this thesis, it was found that when the AuNR@mSiO2 is off resonance of the nanosecond pulsed laser, the thermal reshaping is more controllable for AuNR@mSiO2. The slight blue shift helped to form sealed cavities. After pulsed laser irradiation, the gap size of AuNRs@mSiO2 was found to be controlled by tunning the LSPR band positions to the wavelength of pulsed laser either (on resonance) or (off resonance). Finally, I introduce a new route for fabrication an advantageous dual AuNR@Cavity@mSiO2 of well-controlled and reproducible cavity and high efficiency for photothermal therapy in the near-infrared biological window (700-800 nm) with high porosity for potential drug uploading without influencing the absorption spectra.