Directed assembly and concentrating of micro/nanoparticles, cells, and vesicles via low-power near-infrared laser generated plasmonic microbubbles

Directed assembly and concentrating of micro- and nanoparticles via laser generated plasmonic microbubbles in a liquid environment is an emerging technology. For effective heating, visible light has been primarily employed in existing demonstrations. In this paper, we demonstrate a new plasmonic platform based on nanoporous gold disk (NPGD) array. Thanks to the highly tunable localized surface plasmon resonance of the NPGD array, microbubble of controlled size can be generated by near-infrared (NIR) light. Using NIR light provides several key advantages over visible light in less interference with standard microscopy and fluorescence imaging, preventing fluorescence photobleaching, less susceptible to absorption and scattering in turbid biological media, and much reduced photochemistry, phototoxicity and whatsoever. The large surface-to-volume ratio of NPGD further facilitates the heat transfer from these gold nanoheaters to the surroundings, achieving unprecedented low-power operation. While the microbubble is formed, the surrounding liquid circulates and direct microparticles randomly dispersed in the liquid to the bottom NPGD surface, yielding unique assemblies of microstructures. Such capability can also be employed in concentrating suspended colloidal nanoparticles at desirable sites and with preferred configuration, both enhancing the sensor performance. In addition to various micro- and nanoparticles, the plasmonic microbubbles are also shown to collect biological cells and nanovesicles. By using a spatial light modulator (SLM) to project the laser in arbitrary patterns, parallel assembly can be achieved to fabricate an array of clusters. These assemblies have been characterized using optical microscopy, scanning electron microscope, hyperspectral localized surface plasmon resonance imaging and hyperspectral Raman imaging.