Development of Laser-Induced Nano-Implosion for a Localized Reaction Field

Near-infrared dyes can convert photons from a 1064-nm YAG laser into heat with a high efficiency. Nanoparticles can also be utilized as a shock-wave source and a microscopic reactor via effective use of their infrared absorption, laser-induced breakdown, and optical near-field. Our 2-year research has aimed at the following two purposes: (1) By combining spherical molecular aggregates (such as liposomes and nanoparticles) with infrared dyes, we generate spherical shock-waves that are spatially localized in nano- and micrometer scales to achieve laser-induced nano-implosion; and (2) we utilize hot spots caused by implosion or near-field as a nano-reactor for application to photochemical reactions. We constructed a laser-triggered microscopy system with our CCD microscope and precision stages purchased with this grant, and conducted a series of experiments using liposomes, silver nanoparticles, silver-coated silica nanoparticles (nanoshells), silver microshells, poly-lactide nanoparticles, carbon nanotubes, and hydroxypropyl cellulose (HPC). We also performed structural analyses of metal complexes for future application to dyes and molecular probes. Laser-induced rupture dynamics of dye-doped liposomes was observed by microscopy, in which the process triggered by a single pulse was found to retain spherical symmetry. The possibility of nano-implosion was examined by the Mie-field calculation and photoacoustic simulations. When the clusters were irradiated with a laser pulse, hot spots were created via the localized electromagnetic field, from which breakdown emissions were observed. It suggests self-concentration of optical energy density, which is helpful in utilizing low-energy incident light. In HPC suspensions, enhancement of optical energy transfer and amplified spontaneous emission was observed, owing to the Mie near-field and multiple scattering. These findings are promising for future applications to a variety of chemical reactions.