Numerical Simulations of Double-Well Optical Potentials in All-Dielectric Nanostructures for Manipulation of Small Nanoparticles in Aqueous Media

The manipulation of molecules placed in close proximity to a liquid is crucial for understanding their interactions, as in the study of antibiotics against bacteria. This can, in principle, be realized with plasmonic optical tweezers, but the heating of metals leads to the denaturing of biomolecules. In this work, we demonstrate that slotted all-dielectric nanodisks made of amorphous silicon (a-Si) exhibit double-well optical potentials, which can be used to stably trap dielectric nanoparticles with radii as small as 15 nm using infrared wavelengths where there is no optical loss (no heating) for a-Si. The latter is important to avoid heating the surrounding environment, which in turn, generates fluid convection currents that would compromise optical trapping. The trapping of one and two nanoparticles (even with different morphologies) in water is demonstrated in numerical results for an all-dielectric nanostructure, which can be obtained with standard materials and nanofabrication methods. The trapping forces are only slightly affected by the morphology of the small dielectric nanoparticles, thus indicating that the trapping approach may be applied to a variety of biomolecules.