This thesis describes a study of the synthesis and characterisation of a new family of cationic alkane-thiolate and -selenolate compounds bearing a phosphonium (or phosphine oxide) head group, and the applications as ligands for the stabilisation of gold nanoparticles. The ability of these cationic phosphonium gold nanoparticles as substrates for the detection of negatively charged biomolecules has also been explored. In chapter 1, topics concerning the synthesis of functionalised gold nanoparticles, their biorecognition properties, the application of these nanoparticles in the biomedical field and gold nanoparticles stabilised with phosphorus-containing ligands, are outlined in a literature review.Instrument details of the analytical methods employed to characterise all the compounds and nanoparticles obtained in the study are outlined in Chapter 2. The syntheses and structural characterisation by NMR, ESMS and X-ray crystallography of cationic phosphonium-containing ligands are described in Chapters 3 to 5. Chapter 3 contains the description of the synthesis of phosphonioalkylthiosulfate zwitterions. The synthesis of related phosphonioalkylselenide compounds is presented in Chapter 4, and Chapter 5 is concerned with the synthesis of phosphonioalkylthioacetate and related phosphine oxide ligands. In Chapter 6, the preparation of the cationic phosphonium-functionalised gold nanoparticles using the phosphonium-containing compounds as protecting ligands, in a two-phase liquid-liquid (DCM-H[2]O) and one phase (ethanol) systems, is described. This chapter also contains details of characterisation of these nanoparticles by NMR, XPS and TEM. The ability of the cationic phosphonium gold nanoparticles to interact with RNA and cDNA, and the potential of using these nanoparticles as biorecognition systems was investigated by the Biacore Surface Plasmon Resonance technique and this work is described in Chapter 7. Finally, a summary of conclusions and some suggestions for future work are presented in Chapter 8
