Fano resonant Ge2Sb2Te5 nanoparticles realize switchable lateral optical force

Tun Cao, Libang Mao, Dongliang Gao, Weiqiang Ding and Cheng Wei Qiu

Sophisticated optical micromanipulation of small biomolecules usually relies on complex light, e.g., structured light, highly non-paraxial light, or chiral light. One emerging manipulation is to employ chiral light to drive the chiral nanoparticle along the direction perpendicular to the light propagation, i.e., the lateral optical force. Here, we theoretically study the lateral optical force exerted by a merely Gaussian beam. We for the very first time demonstrate that the Fano resonances(FRs) of the Ge2Sb2Te5 (GST) phase-change nanoparticle encapsulated with Au shell could enable a conventional Gaussian laser to exert lateral force on such a dielectric GST nanoparticle, attributed to the strongly asymmetric energy flow around the spheres 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 biomolecule to the outer surface of the phase-change nanoparticle, the particle behaves as a direction-selective vehicle to transport biomolecule along opposite directions, at pre-assessed states of the Ge2Sb2Te5 core correspondingly. Importantly, the origin of reversal of lateral optical forceis further unveiled by the optical singularity of Poynting vector. Our mechanism by tailoring FRs of phase-change nanoparticles, not just limited to GST, may bring a new twist to optical micromanipulation and biomedical application.

DOI