Plasmonic optical trapping of nanoparticles using T-shaped copper nanoantennas.

We demonstrate the optical trapping of single dielectric nanoparticles in a microfluidic chamber using a coupled T-shaped copper plasmonic nanoantenna for studying light-matter interaction. The nanoantenna is composed of two identical copper elements separated by a 50 nm gap and each element is designed with two nanoblocks. Our nanoantenna inherits three different advantages compared to previous plasmonic nanoantennas, which are usually made of gold. First, copper is a very promising plasmonic material with its very similar optical properties as gold. Second, copper is comparably cheap, which is compatible with industry-standard fabrication processes and has been widely used in microelectronics. Third, the trapping area of tweezers is expanded due to the intrinsic Fabry-Perot cavity with two parallel surfaces. We present finite element method simulations of the near-field distribution and photothermal effects. And we perform Maxwell stress tensor simulations of optical forces exerted on an individual nanoparticle in the vicinity of the nanoantenna. In addition, we examine how the existence of an oxide layer of cupric oxide and the heat sink substrate influence the optical trapping properties of copper nanoantennas. This work demonstrates that the coupled T-shaped copper nanoantennas are a promising means as optical nanotweezers to trap single nanoparticles in solution, opening up a new route for nanophotonic devices in optical information processing and on-chip biological sensing.