  Circular dichroism (CD), induced by chirality, is an important tool for
manipulating light or for characterizing morphology of molecules, proteins,
crystals and nano-structures. CD is manifested over a wide size-range, from
molecules to crystals or large nanostructures. Being a weak phenomenon (small
fraction of absorption), CD is routinely measured on macroscopic amount of
matter in solution, crystals, or arrays of fabricated meta-particles. These
measurements mask the sensitivity of CD to small structural variation in
nano-objects. Recently, several groups reported on chiroptical effects in
individual nanoscale objects: Some, using near-field microscopy, where the
tip-object interaction requires consideration. Some, using dark field
scattering on large objects, and others by monitoring the fluorescence of
individual chiral molecules. Here, we report on the direct observation of CD in
individual nano-objects by far field extinction microscopy. CD measurements of
both chiral shaped nanostructures (Gammadions) and nanocrystals (HgS) with
chiral lattice structure are reported.
