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Synthesis and Manipulation of Nanoparticles

Leech, R; (2014) Synthesis and Manipulation of Nanoparticles. Doctoral thesis , UCL (University College London).

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This thesis investigated the synthesis of a series of water-­‐soluble metal and semiconductor nanoparticles followed by an investigation into their applications as non-­‐antibiotic based antimicrobial agents and to plasmonic structures. Nanoparticles exhibit unique chemical, physical and optical properties unseen in bulk material. These properties can be tuned with the particle dimensions and surface groups to be exploited in biological, chemical, optical and electronic applications. Before the properties can be used however, robust and reliable synthetic procedures must be developed to produce nanoparticles with the desired properties. Initially, water-­‐soluble silver nanoparticles were synthesized stabilized with a series of capping thiols with varying chain length and functional groups. The stability and solubility of the particles was evaluated. Nanoparticles stabilized with tiopronin proved to be the most stable and versatile. These particles were synthesized in diameters from 5.6 to 11.4 nm and proved to be sufficiently stable to be purified and characterized as conventional inorganic materials. The stability and versatility of the tiopronin ligand was demonstrated by its application to produce analogous copper nanoparticles with a diameter of 2.6 nm and by the conjugation of the molecular dye toluidine blue O to the surface of silver particles without their aggregation. The emergence of antibiotic resistant strains of bacteria has created the demand for non-­‐antibiotic based antimicrobials. Silver and copper metals have a proven antimicrobial activity and by producing water soluble nanoparticles the delivery of the metal to and into the bacteria is improved. The tiopronin stabilized silver and copper particles were tested for antimicrobial activity against a range of bacteria including E.coli and S.aureus. Effective bactericidal action was achieved with silver and copper particle concentrations of 50 μg ml-­‐1 and 1000 μg ml-­‐1 respectively. Toluidine blue O (TBO) is an effective photosensitizer for antimicrobial applications. Testing the TBO functionalised silver particles for a light activated antimicrobial activity against MRSA showed the activity of the dye to be enhanced by conjugation to the particle surface. The strong interaction of metallic nanoparticles with light has allowed the development of the new field of plasmonics. In these applications, the surface plasmon is used to guide light energy akin to electrical current in electronics. To produce waveguides, nanoparticles must be assembled into ordered structures. Inter-­‐particle attractions such as hydrogen bonding can be used to hold nanoparticles together. A protocol was developed where tiopronin stabilized silver nanoparticles were assembled into ultra-­‐high aspect ratio arrays. The assembly was initiated by sonication and self-­‐templated by excess ligands in the solution. Adjusting the concentration during sonication allowed chains over a micron in length to be assembled with widths ranging from a single particle to ribbons several particles wide. Having demonstrated tiopronin stabilized metal nanoparticles to be very stable, biologically compatible and capable of assembly the ligand system was applied to semiconductor quantum dots. Organic soluble cadmium selenide quantum dots were synthesized with diameters from 3.4 to 4.9 nm and their surfaces passivated with the overgrowth of a zinc sulphide shell. The ligands were then exchanged with tiopronin to give hydrophilic quantum dots with a fluorescent profile to match the absorption maximum of toluidine blue O. Interactions between the quantum dots and dye molecules in solution together were investigated optically.

Type: Thesis (Doctoral)
Title: Synthesis and Manipulation of Nanoparticles
Language: English
Keywords: Nanoparticles, Silver, Copper, Quantum Dots, Antimicrobial
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1425278
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