title: Fano resonant Ge2Sb2Te5 nanoparticles realize switchable lateral optical force.
abstract: Sophisticated optical micromanipulation of small biomolecules usually relies on complex light, e.g., structured light, highly non-paraxial light, or chiral light. One emerging technique is to employ chiral light to drive the chiral nanoparticle along the direction perpendicular to the propagation of the light, i.e., the lateral optical force. Here, we theoretically study the lateral optical force exerted by a entirely Gaussian beam. For the very first time we demonstrate that the Fano resonances (FRs) of the Ge2Sb2Te5 (GST) phase-change nanoparticles encapsulated with Au shells could enable a conventional Gaussian laser to exert a lateral force on such a dielectric GST nanoparticle, attributed to the strongly asymmetric energy flow around the sphere in the dipole-quadrupole FRs. More interestingly, the direction of this lateral force could be reversible during the state transition (i.e., from amorphous to crystalline). By bonding small biomolecules to the outer surface of the phase-change nanoparticle, the particle behaves as a direction-selective vehicle to transport biomolecules along opposite directions, at pre-assessed states of the Ge2Sb2Te5 core correspondingly. Importantly, the origin of the reversal of the lateral optical force is further unveiled by the optical singularity of the Poynting vector. Our mechanism of tailoring the FRs of phase-change nanoparticles, not just limited to GST, may bring a new twist to optical micromanipulation and biomedical applications.
authors.affiliation: Department of Biomedical Engineering, Dalian University of Technology, Dalian 116024, China. caotun1806@dlut.edu.cn.
authors.forename: Tun
authors.initials: T
authors.lastname: Cao
authors.affiliation: Department of Biomedical Engineering, Dalian University of Technology, Dalian 116024, China. caotun1806@dlut.edu.cn.
authors.forename: Libang
authors.initials: L
authors.lastname: Mao
authors.affiliation: College of Physics, Optoelectronics and Energy & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006, China.
authors.forename: Dongliang
authors.initials: D
authors.lastname: Gao
authors.affiliation: Department of Physics, Harbin Institute of Technology, Harbin 150001, China.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Ding
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Republic of Singapore. eleqc@nus.edu.sg.
authors.forename: Cheng-Wei
authors.initials: CW
authors.lastname: Qiu