Circular Dichroism: A Tool for Characterizing Nanoparticles and Bio-Molecules

Circular dichroism (CD) is the differential absorption of left- and right-handed circularly polarized light. This phenomenon is exhibited in the absorption bands of optically active molecules and nanoparticles. Magnetic CD spectroscopy serves as an excellent tool to track and control the distribution of ions within the spinel lattice of ferrite nanoparticles assisting in the development of general preparation schemes of stoichiometrically controlled multi-cation oxide nanocrystals. The correlation between natural circular dichroism and plasmonics gives rise to two different phenomena. An enhanced CD signal is obtained when chiral molecules are adsorbed onto noble metal nanoparticles, enabling the development of a highly sensitive semi-analytical technique similar to other enhanced spectroscopic techniques (e.g. SERS, SEIRA, SEF, SEMO). The growth of silver nanoparticles in a DNA scaffold resulted in a rather surprising discovery that the nanoparticles were, in fact, chiral.