Optical trapping and tracking of nanoparticles using plasmonic nanoapertures and dielectric nanoantennas

© 2019 Dr. Zhe XuThis dissertation demonstrates the optical trapping and direct tracking of single nanoparticles using a plasmonic double nanohole aperture in a gold film and an all-silicon nanoantenna on a silicon substrate. For both structures, temperature rises that are modest have been predicted, especially for the all-silicon nanoantenna. Fluorescence microscopy is used to observe the optical trapping process during trap-and-release events and to track the position of, and fluorescent emission from, single trapped nanoparticles as a function of time. The nanoparticles consist of fluorescent polystyrene nanospheres with diameters of 20 nm and 100 nm and streptavidin-coated CdSe/ZnS quantum dots. By analysing the Brownian motion of the trapped nanoparticles using fluorescence imaging, we present a quantitative analysis of the dynamics of the trapped nanoparticles, determining quantities such as the effective trapping stiffness. Comprehensive simulations are also performed to gain insight into the trapping process, including of the distributions of the near fields, temperature increase, fluid velocity, optical force and potential energy. Optical forces exerted on nanoparticles are determined using the rigorous Maxwell stress tensor method. Langevin equation simulations are performed to model the particle trajectories with Brownian motion. Other experiments reported include the two-photon excitation of fluorescence from trapped nanoparticles, the transport of nanoparticles relative to an array of nanoantennas via software-controlled movement of the chip, and the trapping and transport of multiple nanoparticles simultaneously