Synergistic effect in two-phase laser procedure for production of silver nanoparticles colloids applicable in ophthalmology
This work reports on the production of Ag nanoparticles (AgNPs) in water solution based upon two-phase pulsed laser procedure for ophthalmological therapeutic approaches. In this case, the AgNPs should be less then 10 nm and have a narrow size distribution. Nanoparticles of this sized-scale are capable to penetrate the complex ocular barriers, ensuring effective non-invasive drug delivery to retina. In the first phase, AgNPs larger than 20 nm were fabricated via laser ablation of a Ag target under water by irradiation with a fundamental wavelength of 1064 nm generated by a Nd:YAG laser. During the second phase, to reduce the mean size of the as-obtained nanoparticles and properly adjust the size distribution, the water colloids were additionally irradiated by ultraviolet harmonics (355 nm and 266 nm) from the same laser source. The effect of the key laser parameters - wavelength, fluence and laser exposure time - upon the nanoparticles morphology was studied. The most suitable post-ablation treatment of initial colloids was obtained by consecutive irradiation with the third (355 nm) and the fourth (266 nm) harmonics of the fundamental laser wavelength. By using this approach synergistic effect between two mechanisms of light absorption by AgNPs was induced. As a result contaminant-free colloids of AgNPs with a size inferior to 10 nm and a quite narrow size distribution with a standard deviation of 1.6 nm were fabricated. The toxic effect of the as-produced AgNPs on Gram-positive and Gram-negative bacteria and Candida albicans was explored. The most efficient action was reached against Pseudomonas aeruginosa and Escherichia coli. Potential application of the synthesized AgNPs colloidal aqueous solutions with antimicrobial action as a non-invasive method for ocular infections prevention and treatment was proposed.