  We put forward an enantioselective method for chiral nanoparticles using
optical tweezers. We demonstrate that the optical trapping force in a typical,
realistic optical tweezing setup with circularly-polarized trapping beams is
sensitive to the chirality of core-shell nanoparticles, allowing for efficient
enantioselection. It turns out that the handedness of the trapped particles can
be selected by choosing the appropriate circular polarization of the trapping
beam. The chirality of each individual trapped nanoparticle can be
characterized by measuring the rotation of the equilibrium position under the
effect of a transverse Stokes drag force. We show that the chirality of the
shell gives rise to an additional twist, leading to a strong enhancement of the
optical torque driving the rotation. Both methods are shown to be robust
against variations of size and material parameters, demonstrating that they are
particularly useful in (but not restricted to) several situations of practical
interest in chiral plasmonics, where enantioselection and characterization of
single chiral nanoparticles, each and every with its unique handedness and
optical properties, are in order. In particular, our method could be employed
to unveil the chiral response arising from disorder in individual plasmonic
raspberries, synthesized by close-packing a large number of metallic
nanospheres around a dielectric core.
