Narband, N.; (2009) Nanoparticles and photosensitisers; their interactions and antibacterial properties. Doctoral thesis , UCL (University College London).

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Abstract

This work reports on the coupling of light activated antimicrobial (LAA) agents with gold nanoparticles to provide new materials that displayed enhanced antimicrobial properties. A versatile and robust approach to the synthesis of gold-thiol-photosensitiser light activated antimicrobials has been developed. In the synthetic approach the thiols attached to the gold nanoparticles were tiopronin and glutathione. The photosensitisers attached to the thiols were toluidine blue and tin chlorin e6 respectively. It was found gold-tiopronin-toluidine blue nanoparticles at 1 µM concentration were efficient as light activated antimicrobials, that had a reduction of colony forming units (cfu) of S. aureus by 4.5 log 10 compared with, 0.5 log 10 for toluidine blue at the same concentration. The attachment of photosensitisers to thiol protected gold nanoparticles enhanced the lethal photosensitisation of bacteria. The second approach was mixing of charge stabilised gold nanoparticles with various photosensitisers. When charge stabilised gold nanoparticles when mixed with toluidine blue (20 µM), showed a reduction in colony forming units (cfu) for S. aureus of 2.5 log 10 compared with 1.5 log 10 for only toluidine blue at the same concentration. This established that covalent attachment of the photosensitiser was not necessary for the enhancement in the lethal photosensitisation of bacteria. Also, it was discovered that certain dyes which have basic, cationic natures have different interactions with charge stabilised gold nanoparticles. A separate study focusing on semi-conductor quantum dots and the photosensitiser toluidine blue was undertaken to investigate any relationship between nanoparticles and photosensitisers. It was found that semi-conductor quantum dots enhance the effect of toluidine blue in the lethal photosensitisation of bacteria. An excess of a 1.7 log 10 enhancement in bacterial kill was observed with quantum dot concentration of 0.0075 µM and toluidine blue concentration of 20 µM. In summary, the efficacy of photosensitisers can be enhanced by the presence of nanoparticles of gold and CdSe.

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