|
Optical tweezers have emerged as a powerful technique for non-invasive trapping and manipulation of microscopic objects. The diffraction limit precludes the low power trapping of nanoscale objects with optical tweezers. Plasmonic optical tweezers, which employ resonant plasmonic nanoantenna to confine electromagnetic fields to the nanoscale have been developed to enable the optical trapping of nanoscale objects. A peculiar advantage of plasmonic tweezers is the capability to not only trap nanoscale objects and biomolecules but also to perform spectroscopy on the trapped object. Such new capability would benefit from high throughput trapping and sorting of nanoscale objects on a plasmonic substrate. To meet this need, we present a thermoplasmonic nanohole metasurface platform for high throughput trapping and size-based sorting of nanoscale particles. The thermoplasmonic metasurface comprises of sub-wavelength nanoholes patterned on a gold film. A microfluidic channel is constructed over the nanohole metasurface region and another substrate is placed over it, to create a parallel plate capacitor configuration. The illumination of the thermoplasmonic nanohole metasurface causes photothermal heating and a thermal gradient in the fluid. The application of an AC electric field across the fluid element creates an electrothermoplasmonic microfluidic vortex. This vortex enables the long-range capture of the nanoparticles for rapid trapping and assembly. Additionally, the thermoplasmonic nanohole metasurface structure creates a distortion of the applied AC electric field. The tangential component of the AC electric field induces an AC electro-osmotic flow. By harnessing the interplay of these forces with the optical gradient force, we demonstrate several features including trapping, dynamic manipulation of nanoparticles, and size-dependent sorting of nanoscale particles.
|
