Selective optical manipulation of nanoparticles according to their chirality is a challenge due to the relatively small size of the chirality-dependent optical force. Here, we introduce the evanescent field of optical nanofibres as a promising tool for such manipulation. Using circularly polarised fibre modes, we demonstrate strongly chirality-selective optical transport of a chiral nanoparticle. Our experiments, backed by simulations, show that right- and left-handed circularly polarised modes produce clearly distinct velocities of optically trapped chiral nanoparticles along the nanofibre. Furthermore, using a counterpropagating mode configuration, the non-chiral component of the optical force can be cancelled, yielding selective forward and backward transport. The chiral optical force was found to be significant even for particle ensembles with natural variations in size and form, implementing optical separation of chiral enantiomers at the scale of 100 nm. Further development towards waveguide-assisted enantioselective manipulation approaching the molecular scale can be envisaged. The authors demonstrate a method for the manipulation of the motion of chiral nanoparticles, which involves utilising circularly polarised light in an ultrathin optical fibre. The evanescent field of this fibre can both trap and propel particles near the fibre surface, with the direction of the particle motion depending on the circular polarisation state of the light.
Tkachenko et al. (Thu,) studied this question.