Samples of suspended gold nanoparticles in the diameter range 10 nm to 100 nm were subjected to a single 7 ns pulse from a 532 nm laser to determine the effects of laser power on particle size distribution, mean size, and morphology. The experimental techniques used were dynamic light scattering (DLS), electrospray-dynamic mass analysis (ES-DMA) which provides particle size distributions, ultraviolet-visible absorption spectroscopy (UV-VIS), and transmission electron microscopy (TEM). For 60 nm particles, a laser pulse of 10 mJ/cm2 was sufficient to produce observable changes. In the range 10 mJ/cm2 72 mJ/cm2 DLS indicated very little change in mean particle size, but a more than threefold reduction in the polydispersity index (significantly tightened distribution) and a decrease in scattering intensity. TEM showed that the particles became highly spherical and that there was a growing population of particles < 10 nm in size that could not be detected by the other methods. Fused dimers were also observed. At higher power, the mean particle size decreased until all particles were < 10 nm in size. The threshold for observable changes decreased with increasing particle size in the range 10 nm to 60 nm, but increased for 100 nm particles. These results will be useful for potential therapeutic applications for pulse-heated nanoparticles and demonstrate the use of a simple laser treatment for modifying and improving nanoparticle properties.
Citation: Journal of Physical Chemistry C
Pub Type: Journals
nanoparticles, gold, laser ablation, transmission electron microscopy, dynamic light scattering, differential mobility analysis, ultraviolet-visible absorption spectroscopy