| Summary: | Gold nanoparticles (AuNPs) are considered to have significant potential as in photothermal therapy, drug delivery and antibiotic activities due to their optical properties, chemical stability and biocompatibility. AuNP surface functionalisation plays an important role in cellular uptake and producing cellular responses. For this reason, novel AuNPs (5-26 nm) functionalised by a new family of a phosphonioalkylthiosulfate/thioacetate in this thesis, and have been shown to be stable for a period up to 6 months with no obvious evidence for any aggregation. Production of novel cationic phosphonium AuNPs (8-11 nm) by borohydride reduction of a gold (III) salt, dispersed in water or dimethylsulfoxide (DMSO) for their potential use in biomedical applications is outlined in Chapter 2.The environment around cancer cells is known to be mildly acidic with pH of 6.0 to 7.2, which is lower than in healthy cells. Based on the pH factor, AuNPs have shown abilities to induce cancer cell death via a photothermal therapy after aggregation. For this reason, our cationic phosphonium AuNPs were subjected to investigate their stability over time and at a pH range of 3-11. This work is described in Chapter 3. The synthesised AuNPs were primarily characterised using both UV-visible spectra and Dynamic light scattering (DLS). The pH study suggested that the optimum pH range for the AuNP colloidal samples to remain stable ( without aggregation) is between pH 9.2 and pH 5.1. Within this range, the diameters recorded by the DLS were 9.6 ± 0.9 nm, and the aggregation (instability) was noted at pH ˂ 5 and ˃ 9. The structural characterisations of all ligands in this thesis were confirmed by using ATR, ESI-MS and NMR, while the influence of the ligands on the formation and stability of AuNPs was investigated by DLS, TEM and UV-Vis measurements, and described in Chapter 2 to 6.Green methods used to synthesis AuNPs using ascorbic acid, as bio-reducing agent was important nowadays, especially within the biological cells due to its low toxicity. Well-monodispersed AuNPs were prepared by the reduction of KAuCl4 using NaBH4 and ascorbic acid as reducing agents. Using different reducing agent power, obtained different results for AuNPs that functionalised with same conditions in Chapter 4. Small sizes with higher stability up to 6 months were generated when NaBH4 was used as reducing agent. Where AuNPs of different sizes are known to produce contradictory results sometimes in vivo and in vitro bio-application. AuNPs functionlised by di-phosphine oxide thiol ligand are considered to be very active against bacteria, and have broad bio-applications. The work on AuNPs functionlised by novel related phosphine oxide thiols ligands is discussed in Chapter 5.Due to antibiotic drug resistance to some kinds of bacterial infection, development of new antibacterial agents is necessary. This thesis describes a study of the efficiencies of different concentrations of AuNPs (8-17 nm) on non-pathogenic bacteria including, Escherichia coli NCIB 8277 and Staphylococcus aureus ATCC 6538P in (Chapter 6). AuNPs exhibited excellent antibacterial sensitivity to both kinds of bacteria especially at high concentration (30 μL) of AuNPs.
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