Kitching, Hazel; (2017) The synthesis and characterisation of noble metal nanoparticles and their uses in antimicrobial surfaces. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Herein is presented the synthesis and characterization of a range of gold silver and bimetallic nanoparticles using a variety of synthetic routes. Particles of different sizes and shapes were fabricated by using different reaction conditions and capping agents. Mesoscale linear arrangements of tiopronin-capped silver nanoparticles were fabricated using a sonication step. The interaction of all synthesised particles with a range of cationic and anionic dyes was investigated and yielded mixed results. Enhanced absorption of the dye maxima was seen in some cases when combined with citrate-capped gold nanoparticles, with novel dyenanoparticle combinations which exhibit this behaviour reported. Aggregation of these particles was also observed at high concentrations of cationic dyes. It was established that aggregation was not due to increasing ionic strength of the solution as previously postulated but an attractive charge-charge mechanism between the dye molecules and citrate shell. It is well known that dye molecules can act as antimicrobial agents. Literature has shown that conjugation of these dyes with a nanoparticle can enhance the bacterial kill rate. The antibacterial capabilities of citrate-stabilised gold and silver nanoparticles were therefore evaluated against gram positive and gram negative organisms. Excellent kill rates were observed for several novel combinations of dye and nanoparticle. Acridine orange with silver nanoparticles, a previously unreported conjugate, delivered complete kill of both E. coli and S. aureus in five hours both under a white light source and in the dark. This shows potential for further use as a self-sterilising surface due to the potency and rapidity of the bactericidal response. Novelty of the work:: Novel combinations of dyes and nanoparticles that exhibit enhanced optical absorption of the dye maxima were found. Additionally a pre-existing theory concerning the cause of nanoparticle aggregation at high dye concentrations was proven to be incomplete and a new 3 theory proposed. The new dye-nanoparticle combinations were used for antimicrobial testing with excellent results attained for both gram positive and gram negative organisms. Silver nanoparticles were used in conjunction with dyes to make antimicrobial surfaces for the first time. Light and dark kill rates for acridine orange combined with citrate-capped silver nanoparticles show potential for commercialization as antimicrobial surfaces.

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