Selective plasmonic trapping in periodic gold polygon tetramers

Highly bounding light at metal surface by localized surface plasmon resonance (LSPR) improves the optical trapping of nanoparticles, which is called plasmonic trapping. Since LSPR is high related to the geometry of metal structures, the construction of metal nanostructure is extremely significant in the nano-trapping. In this work, the plasmonic trapping of dielectric nanoparticles in periodic gold polygon tetramers is investigated through finite-difference time-domain (FDTD) method. The simulation results of electric field distribution and the corresponding optical force indicate the number of side is quite important to the trapping efficiency that the square tetramers is obviously superior to other ones with more sides. However, this efficiency difference is also related to the size of nanoparticle that it is more sensitive to the smaller nanoparticles. Furthermore, the results also figure out not only trapping efficiency but also the trapping position is greatly influenced by the wavelength of trapping light in the same gold polygon tetramers. All our results open a way to selectively trap nanoparticles with required size at appointed positions, which has extensive application prospects in manipulation of nanoparticles in solution.