Optical Gradient Force on Gold Chiral Nanoparticles

The chiro-optical effects are measured through the spectroscopic methods typified by optical rotation (OR) and circular dichroism (CD). The chiro-optical effect can also appear as the motion of the chiral particles illuminated by the circularly polarized light. When a chiral nanoparticle is optically trapped using a circularly polarized laser beam, the circular polarization (CP) dependent gradient force is expected to be induced on the particle. We investigated the CP-dependent gradient force for the three-dimensionally chiral nanoparticles. The experimental result showed that the gradient force depended on the handedness of CP (left- or right-handed) of the trapping light as well as on the handedness of the particle chirality. The extended aspect of the chiral optical force obtained here can give us novel methodologies for the researches of chirality sensing, manipulation, separation, enantio-selective biological reaction.N