Optically assisted diffusophoretic tweezers using resonant plasmonic bowtie nano-antennas

Abstract: Plasmonic antennas, leveraging localized surface plasmon resonance (LSPR), hold significant promise for efficiently trapping nanoscale particles at low power levels. However, their effectiveness is hindered by photothermal effects in metallic nanoparticles, leading to repulsive thermophoretic forces. To address this limitation, we propose a novel hybrid approach that combines depletion attraction and photothermal effects inherent in plasmonic structures, capitalizing on thermally induced concentration gradients. Through the thermophoretic depletion of polyethylene glycol (PEG) molecules around plasmonic hotspots, we create sharp concentration gradients, enabling precise localization of nanoscopic particles through a synergistic effect with diffusophoretic forces. In our experiments, we successfully demonstrate the trapping and dynamic 2D manipulation of 100 nm polystyrene beads, showcasing the platform's potential for colloidal assembly at the nanoscale. Remarkably, this method maintains highly stable trapping performance even at an incredibly low 2.5 mW laser power, rendering it particularly appealing for applications involving biological species. Our study introduces a promising avenue for the precise and efficient manipulation of sub-nanoscale particles, with wide-ranging implications in nanotechnology, biophysics, and nanomedicine. This research opens up new opportunities for advancing nanoscale particle studies and applications, ushering in a new era of nanoscale manipulation techniques.