Optical radiation forces of focused Gaussian beams on the three-layered microgel particles with near-infrared responses

Wei Ju, Jie Yao, He-Ping Ding, Da-Jian Wu

Optical manipulation of three-layered microgel particles with near-infrared responses is important for drug delivery and release in vivo. In this work, we investigate the optical radiation force (ORF) on a three-layered SiO2–Au–pNIPAM particle in a focused Gaussian beam (FGB) based on Mie scattering theory. As the radius of inner SiO2 core increases to 43 nm, the dipole plasmon resonance of the SiO2–Au–pNIPAM particle moves to ~ 800 nm. In the vicinity of this wavelength, the ORF of the FGB on the SiO2–Au–pNIPAM is always positive due to the strong scattering. As the working wavelength is larger than ~ 1100 nm, the gradient force on the particle becomes stronger than the scattering force, and thus the negative ORF is realized. We focus on negative ORF on the SiO2–Au–pNIPAM, and find that the beam waist radius, the outer gel shell, and the embedding medium all influence the ORF on the SiO2–Au–pNIPAM particle. The present work may be helpful for manipulating three-layered microgel particles, with the negative ORF being particularly important for particle trapping.

DOI