Imaging Circular Dichroism of Single Nanoparticles Using Photothermal Microscopy

Chiral nanoparticles are those nanostructures whose mirror image cannot be superimposed onto each other. Enantiomers of a chiral nanoparticle interact differently with left- and right-circularly polarized light. Circular dichroism (CD) is the differential absorption of left- and right-circularly polarized light. Circular birefringence (CB) or optical rotatory dispersion (ORD) is the rotation of the polarization direction of the linearly polarized light through a chiral medium. CD and CB are respectively related to the imaginary and real part of the dielectric function. Standard detection of CD of single nanoparticles is based on extinction or scattering and thus cannot measure a true CD signal. To detect a true CD signal of a single nanoobject, an absorption-based method is needed.