Plasmonic tweezers based on connected nanoring apertures

TL;DR

This paper demonstrates efficient trapping of single nanoparticles using plasmonic nanoring apertures, achieving high trap stiffness and rapid trapping times, with potential applications in nanoparticle delivery and nanofluidics.

Contribution

It introduces a novel plasmonic nanoring aperture design for nanoparticle trapping, combining experimental and theoretical analysis to optimize trap performance.

Findings

High trap stiffness of 3.50fN/nm/mW for 20nm particles

Trap capture time less than 8 seconds at high particle concentration

Enhanced electromagnetic near-field improves trapping efficiency

Abstract

The manipulation of microparticles using optical forces has led to many applications in the life and physical sciences. To extend optical trapping towards the nano-regime, in this work we demonstrate trapping of single nanoparticles in arrays of plasmonic coaxial nano-apertures with various inner disk configurations and theoretically estimate the associated forces. A high normalised experimental trap stiffness of 3.50fN/nm/mW for 20nm polystyrene particles is observed for an optimum design of 149nm for the nanodisk diameter at a trapping wavelength of 980nm. Theoretical simulations are used to interpret the enhancement of the observed trap stiffness. A quick particle trapping time of less than 8sec is obtained at a concentration of 14$\times$10$^{11}$ particles/ml with low incident laser intensity of 0.59mW/$\mu$m$^{2}$. This good trapping performance with fast delivery of nanoparticles to multiple trapping sites emerges from a combination of the enhanced electromagnetic near-field and spatial temperature increase. This work has applications in nanoparticle delivery and trapping with high accuracy, and bridges the gap between optical manipulation and nanofluidics.