Abstract
Chiral near fields possessing enhanced asymmetry (superchirality), created by the interaction of light with (chiral) nanostructures, potentially provide a route to novel sensing and metrology technologies for biophysical applications. However, the mechanisms by which these near fields lead to the detection of chiral media is still poorly understood. Using a combination of numerical modeling and experimental measurements on an antibody–antigen exemplar system, important factors that influence the efficacy of chiral sensing are illustrated. It is demonstrated that localized and lattice chiral resonances display enantiomeric sensitivity. However, only the localized resonances show a strong dependency on the structure of the chiral media detected. This can be attributed to the ability of birefringent chiral layers to strongly modify the properties of near fields by acting as a sink/source of optical chirality, and hence alter inductive coupling between nanostructure elements. In addition, it is highlighted that surface morphology/defects may amplify sensing capabilities of localized chiral plasmonic modes by mediating inductive coupling.
Highlights
Optical Chirality (C) C ≡ ε0 2 E·∇ Â E þ B·∇ B (1)where E and B are electric an magnetic fields, is a conserved property of light,[4,22,23] like energy, and is equivalent to optical spin density
Metamaterials consisting of periodic arrays of gammadia display large levels of optical activity in the visible and near IR region of the spectrum.[29,30,31,32]
Gammadia-based metamaterials of both pure enantiomorphs and racemic structures have been used for the detection of chiral molecular materials.[8,30]
Summary
Where E and B are electric an magnetic fields, is a conserved property of light,[4,22,23] like energy, and is equivalent to optical spin density. The differential absorption of CPL (dissipation of optical chirality) by chiral media is the basis of the chiroptical technique circular dichroism. The central premise of this study is that chiral birefringent layers act as efficient sinks of near field optical chirality. This causes significant divergence in the reciprocity of the C and intensities of fields possessed by left- (LH) and right-handed (RH) nanostructures. This causes asymmetric changes in the chiroptical properties of LH and RH structures, measured in the far field, which enhances chiral sensing capabilities
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