Plasmonic nanotweezers based on Au bowtie nanoantenna arrays for manipulation of nano-to-macroscopic objects

Plasmonic optical traps, or plasmonic “nanotweezers”, have emerged as an attractive alternative for optical manipulation because they circumvent the diffraction limit, producing highly confined and enhanced fields that both relax constraints for microparticle manipulation and offer a route for improving nanoparticle trapping. Here, we present an overview of the use of Au bowtie nanoantenna arrays (BNAs) for plasmonic nanotweezers. We show that optical absorption by the BNAs creates convection currents that resemble a Rayleigh-B´enard pattern and that an absorptive substrate, e.g. Indium-Tin-Oxide, is crucial to achieve large convection velocities. Furthermore, we demonstrate phase-like behavior of trapped particles and that the adhesion layer material and nanostructure orientation strongly affect trapping behavior. In addition, we discuss the use of a femtosecond- pulsed source in plasmonic nanotweezers and demonstrate that the fs pulses (1) augment the near-field optical forces compared to comparable, continuous-wave nanotweezers, and (2) increase the diagnostic capabilities of plasmonic nanotweezers by providing access to the nonlinear optical response of trapped species. Finally, we show for the first time that plasmonic nanoantennas are an effective tool for manipulation objects up to at least 50 μm in diameter. Using low-numerical aperture illumination (0.25-0.6 NA), we show that manipulation of these “macroscopic” objects is facilitated by increasing the number of illuminated nanostructures participating in the trapping event. These results open up a new avenue for the usage of plasmonic nanotweezers and may have applications for manipulating Eukaryotic cells, studying self-organization/aggregation of cells, and micro-scale manufacturing.