Surface Enhanced Circular Dichroism by Electric and Magnetic Dipole Resonance of Cross Shaped Nanoholes

TL;DR

This paper demonstrates that cross-shaped nanoholes can significantly enhance circular dichroism signals, reaching up to 450 times the molecular inherent CD, by overlapping electric and magnetic dipole resonances for improved detection of molecular chirality.

Contribution

The study introduces a novel nanostructure, the cross-shaped nanohole, for surface-enhanced circular dichroism, with tunable parameters to optimize CD signal enhancement.

Findings

Maximum enhancement of 450-fold of molecular CD.

Overlapping electric and magnetic dipole resonances is crucial for enhancement.

Structural parameters can tune the enhancement factor and peak location.

Abstract

The near-field interaction of plasmonic nanostructures and chiral molecules induces circular dichroism in achiral nanostructure. The induced circular dichroism (ICD) strength is several orders greater than the molecular inherent CD (MCD), and it generally appears at visual range (VR) where the CD signal is easily detectable. Therefore, the ICD is considered as a potential method to detect single molecular chirality. In this study, cross shaped nanohole (CSN) is proposed for enhancing the MCD signal. The maximum enhancement of the structure reached 450 folds of molecular inherent MCD. Through analysis of the surface plasmon resonance mode, it is found that overlapping of the electric dipole (ED) and magnetic dipole (MD) surface plasmon resonance (SPR) in CSN is essential for the CD enhancement. Furthermore, we investigated the effects of the thickness of structure, length of longer and shorter arms of nanohole, the displacement of shorter arm of the nanohole and x period of CSN on the circular dichroism enhancement, and found the enhancement factor and location of CD enhancement peak to be tunable by the structural parameters