Anisotropy-enhanced optical pulling force on coated nanoparticles due to Fano resonance

Highlights: • There is anisotropy boundary for the reversal of the optical action between optical repulsion and optical attraction. • Maximal pulling force at Fano resonance could be enhanced by tuning anisotropy of nanoparticle. • The nanoparticles can be sorted with specified anisotropy at given incident wavelength. • Broad wavelength to achieve giant pulling force is obtained for the negative permittivity of anisotropic core. • The numerical results provide potential applications in optical trapping, sorting and transporting anisotropic nanoparticles. We investigate the effect of radial anisotropy on the optical force exerted on the anisotropic-core/plasmonic-shell nanoparticles under the illumination of the zeroth order Bessel beam based on extended Mie theory and Maxwell's stress tensor method. Optical pulling force on such core-shell nanoparticles at Fano resonance is found, and such pulling force could be enhanced when the radial permittivity is much larger than the tangential permittivity of the anisotropic core. Furthermore, much strong pulling force is easy to be achieved for the negative permittivity of the anisotropic core. The optical pulling force could be also tunable by adjusting the anisotropic parameter, which can be used as the implement of particle selection. Our results will offer future prospects of nano-manipulation and provide the freedom of optical sorting and selection of nanoparticles.