Circular Differential Scattering Spectroscopy for the Characterization of Single Chiral Nanostructures: Fundamentals, Development, and Perspectives

Circular differential scattering (CDS) spectroscopy has been developed as a powerful method for the characterization of single chiral nanostructures and recently expanded with versatile capabilities. The core of CDS is a dark‐field microscope, which is modified by including left and right circular polarizations in either the excitation or detection optical path to measure the differential scattering spectra between both circular polarizations, from single nanostructures. Compared to traditional circular dichroism (CD) spectroscopy for ensemble samples, CDS spectroscopy offers single‐particle resolution, thereby resolving subtle chiral features of individual nanostructures and avoiding the averaging effect in racemic mixtures. CDS spectroscopy has evolved into a robust analytical method, recently achieving detection limits as low as 1.5%—a dramatic reduction from more common values of 10%. CDS has become a key technique in exploiting the chiroptical properties of intrinsic plasmonic chiral nanocrystals and their interactions with substrates, optical activity amplification of molecules by plasmon resonances, chiral assemblies of plasmonic particles, plasmonic nanocrystal growth, unidirectional scattering of chiral particles, enantiomeric switching of reconfigurable metamolecules, etc. In the future, CDS spectroscopy aims at pushing the limit of optical sensitivity to the identification of single molecule chirality. We review herein the fundamentals, development, and perspectives of CDS spectroscopy.