Abstract
Abstract Surface-enhanced circular dichroism (SECD) of chiral molecules adsorbed on plasmonic nanostructures can substantially enhance chiroptical molecular signals by several orders, which is otherwise very weak to be directly measured. Several mechanisms were proposed to explain this extreme enhancement, but the exact mechanism is still controversial. We investigate strong higher-order multipole contribution to SECD near plasmonic nanostructures using the superposition T-matrix method and discuss how 3-dimensional full-field simulations implementing a homogeneous chiral medium have succeeded in the reconstruction of the extreme enhancement. We also discuss how theoretical studies modeling chiral molecules based on dipole approximation have failed to reconstruct the extreme enhancement and show that SECD enhancement of such chiral dipoles is directly governed by optical chirality enhancement. In addition, strong multipolar transitions in subwavelength chiral plasmonic nanoparticles are discussed based on the T-matrix. This work reviews theoretical frameworks describing chiral molecules, demonstrates significant contribution of a multipolar transition on the extreme SECD enhancement near plasmonic nanostructures, and emphasizes the importance of a multipolar transition in chiral nearfield interaction.
Highlights
Surface-enhanced spectroscopic techniques utilizing plasmonic nanostructures have succeeded in the sensitive measurement of molecular signatures, and practical applications include surface-enhanced Raman spectroscopy where extreme enhancement up to single or few molecule levels has been demonstrated [1]
We investigate strong higher-order multipole contribution to Surface-enhanced circular dichroism (SECD) near plasmonic nanostructures using the superposition T-matrix method and discuss how 3-dimensional full-field simulations implementing a homogeneous chiral medium have succeeded in the reconstruction of the extreme enhancement
We discuss how theoretical studies modeling chiral molecules based on dipole approximation have failed to reconstruct the extreme enhancement and show that SECD enhancement of such chiral dipoles is directly governed by optical chirality enhancement
Summary
Surface-enhanced spectroscopic techniques utilizing plasmonic nanostructures have succeeded in the sensitive measurement of molecular signatures, and practical applications include surface-enhanced Raman spectroscopy where extreme enhancement up to single or few molecule levels has been demonstrated [1]. This surface enhancement scheme has been applied to increase very weak intrinsic chiroptical signals of chiral molecules (CMs), which allows us to access extra information about handedness of CMs and structural conformation of biomolecules. In this paper, we use the superposition T-matrix method to account for multiple scattering between NP and CM in a numerically exact manner; see Section S2 in Supplementary Material for more details
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