Synthesis, Characterisation and Biological Activity of Silicon Nanoparticles Functionalised by Anticancer Compounds

Abstract Silicon Nanoparticles (SiNPs) are non-toxic materials particularly suitable for various biomedical applications. They exhibit unique optical properties for use in bioimaging and diagnostic applications. To exploit these aspects, this thesis explores the synthesis, characterisation and biological activity of SiNPs functionalised by anticancer compounds. Thiourea-based compounds have been shown to represent one of the most promising classes of anticancer agents due to their strong inhibitory activity against Epidermal Growth Factor Receptor (EGFR), overexpression of which is observed in common types of cancer cells. Conjugation of thiourea compounds in nanosystems presents one potential approach to target such cells. In this thesis, successful synthesis of novel thiourea-functionalised SiNPs was undertaken and their physiochemical properties were investigated by photoluminescence emission and elemental analysis. In vitro cytotoxicity assay was employed to evaluate the effect of SiNPs. Confocal microscopy images demonstrate SiNP internalisation and flow cytometry data confirms receptor-mediated targeting in cancer cells. Isothiocyanates (ITCs) can prevent the onset of carcinogenesis and act as chemopreventive compounds. ITC-functionalised SiNPs were synthesised using two different methods, initiated from two different types of SiNPs. The surface chemistry of these particles were characterised and their optical properties examined to assess both synthesis approaches. The samples produced from the precursor Br SiNPs exhibit strong photoluminescence and therefore are suitable for uptake studies. The cytotoxicity of ITC SiNPs was evaluated by MTT and their internalisation confirmed using confocal microscopy and flow cytometry assay. Synchrotron-based FTIR microspectroscopy was used as a novel approach to investigate ITC SiNP cell internalisation. Spectral comparison between treated and control cells shows the effect of ITCs, leading to an increase both in protein level in the nuclei, and also in the chance of apoptosis, which increases phospholipid contents. Considering the obtained results, such multifunctional nanosystems have the potential to be applied for further diagnostic and therapeutic applications

Hydrogen-terminated mesoporous silicon monoliths with huge surface area as alternative Si-based visible light-active photocatalysts

Silicon-based nanostructures and their related composites have drawn tremendous research interests in solar energy storage and conversion. Mesoporous silicon with huge surface area of 400 - 900 m2g-1 developed by electrochemical etching exhibits excellent photocatalytic ability and stablility after 10 cycles in degrading methyl orange under visible light irradiation, owing to the unique mesoporous network, abundant surface hydrides and efficient light harvesting. This work showcases the profound effects of surface area, crystallinity, pore topology on charge igration/recombination and mass transportation. Therein the ordered 1D channel array has outperformed the interconnected 3D porous network by greatly accelerating the mass diffusion and enhancing the accessibility of the active sites on the extensive surfaces

Synthesis and characterisation of isothiocyanate functionalised silicon nanoparticles and their uptake in cultured colonic cells

Isothiocyanate functionalised silicon nanoparticles were successfully synthesised for monitored drug delivery.</p

Synthesis of diagnostic silicon nanoparticles for targeted delivery of thiourea to epidermal growth factor receptor-expressing cancer cells

The novel thiourea-functionalized silicon nanoparticles (SiNPs) have been successfully synthesized using allylamine and sulforaphane, an important anticancer drug, followed by a hydrosilylation reaction on the surface of hydrogen terminated SiNPs. Their physiochemical properties have been investigated by photoluminescence emission, FTIR and elemental analysis. MTT assay has been employed to evaluate in vitro toxicity in colorectal cancer cells (Caco-2) and primary normal cells (CCD). The results show significant toxicity of thiourea SiNPs after 72 h incubation in the cancer cell line and the toxicity is concentration dependent and saturated for concentrations above 100 µg/mL. Confocal microscopy images have demon-strated the internalization of thiourea-functionalized SiNPs inside the cells. Flow cytometry data has confirmed receptor-mediated targeting in cancer cells. This nanocomposite takes advantage of the EGFR active targeting of the ligand in addi-tion to the photoluminescence properties of SiNPs for bioimaging purposes. The results suggest that this novel nanosystem can be extrapolated for active targeting of the receptors that are overexpressed in cancer cells such as EGFR using the targeting characteristics of thiourea-functionalized SiNPs and therefore encourage further investigation and development of anticancer agents specifically exploiting the EGFR inhibitory activity of such nanoparticles

Synthesis and characterisation of isothiocyanate functionalised silicon nanoparticles and their uptake in cultured colonic cells.

The functionalisation of silicon nanoparticles with a terminal thiocyanate group, producing isothiocyanate-capped silicon nanoparticles (ITC-capped SiNPs) has been successfully attained. The procedure for the synthesis is a two-step process that occurs via thermally induced hydrosilylation of hydrogen terminated silicon nanoparticles (H-SiNPs) and further reaction with potassium thiocyanate (KSCN). The synthesis was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-Ray photoelectron spectroscopy (XPS). At the same time, the internalisation and the cytotoxicity of the ITC-capped SiNPs in vitro were assessed in two cell lines: Caco-2, human colorectal cancer cells and CCD-841, human colon "normal" cells. The results showed that above concentrations of 15 µg ml-1, the cell viability of both cell lines was depleted significantly when treated with ITC SiNPs, particularly over a 48 hour period, to approximately 20% cell viability at the highest treatment concentration (70 µg ml-1). Flow cytometry was employed to determine cellular uptake in Caco-2 cells treated with ITC SiNPs. It was observed that at lower SiNP concentrations, uptake efficiency was significantly improved for time periods under 12 hours; overall it was noted that cellular uptake was positively dependent on the period of incubation and the temperature of incubation. As such, it was concluded that the mechanism of uptake of ITC SiNPs was through endocytosis. Synchrotron FTIR spectroscopy, by means of line spectral analysis and IR imaging, provided further evidence to suggest the internalisation of ITC SiNPs displays a strong localisation, with an affinity for the nucleus of treated Caco-2 cells