Surface Enhanced Circular Dichroism by Quadrilateral Arranged Nanoholes

TL;DR

This paper introduces quadrilateral nanohole arrays to significantly enhance molecular circular dichroism signals, enabling better detection of molecular chirality in the visible range through plasmonic interactions.

Contribution

The study proposes a novel nanostructure design (QAN) that achieves up to 200-fold enhancement of MCD and explains the underlying mechanisms involving symmetry breaking and resonance mode interactions.

Findings

Maximum 200-fold MCD enhancement achieved.

ICD is enhanced by overlapping electric and magnetic dipole resonances.

Surface structure parameters influence MCD enhancement effectiveness.

Abstract

Circular dichroism (CD) is absorption difference of right-hand and left-hand circularly polarized light by components. CD spectroscopy technique is an important tool for detecting molecular chirality, but the molecular circular dichroism (MCD) is weak and always appears in the ultraviolet (UV) region that is more noisy than visual range (VR). Induced circular dichroism (ICD) arisen from near-field interaction of plasmonic nanostructures and chiral molecules enhances the detection limit of molecular chirality and usually appears in VR. In this study, quadrilateral arranged nanoholes (QAN) are proposed for enhancing the MCD. The maximum enhancement achieved by the structure is about 200 folds of the MCD. Furthermore, we explained the mechanism of ICD which is generated by symmetry breaking of electric field QAN by molecular dipole. We investigated the effect of surface plasmon resonance (SPR) mode on ICD through analyzing the electric dipole (ED) and magnetic dipole (MD) resonance modes. ICD was found to get enhanced as a result of overlapping of ED and MD resonance around QAN. Besides this investigation, we probed the effects of thickness of structure, length of holes and length of periods on the MCD enhancement