Circular Dichroism of Single Particles

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.