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Division of Microbial Diseases, UCL Eastman Dental Institute, University College London, 256 Gray’s Inn Road, London, UK
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Phys. Chem. Chem. Phys., 2009,11, 10513-10518
15 May 2009,
09 Sep 2009
First published online
14 Oct 2009
The interactions of charge stabilised gold nanoparticles with cationic and anionic dyes are reported. The nanoparticles were synthesised by the Turkevich citratereduction method. It was found that when a solution of thiazine dye is titrated against gold citrate hydrosol, at a critical concentration of dye there is an enhanced maximum absorption in the dye. The extinction coefficient is increased up to ten-fold. This enhancement was observed for a number of cationic thiazinedyes, of which methylene blue and toluidine blue are established light-activated antimicrobial agents. The same enhancement was not observed for anionic, acidic dyes such as rose bengal which showed no communication with the gold nanoparticles and showed UV-visibletitration experiments with well formed isosbestic points. By studying the interaction of the dye and gold nanoparticles under conditions of different ionic strength and by using a zetasizer and TEM to measure the gold nanoparticle size it was demonstrated that the cause of enhancement was not due to nanoparticle aggregation. It is proposed that thiazine cationic dyes coordinate around a gold nanoparticle and give significantly enhanced UV-visible absorptions.
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