Enhancement of Optical Chirality Using Metasurfaces for Enantiomer-Selective Molecular Sensing

Sangtae Jeon,Soo Jin Kim

doi:10.3390/app11072989

Abstract

Circular dichroism (CD) is a physical property observed in chiral molecules by inducing the difference of absorption between left- and right-handed circularly polarized light (CPL). Circular dichroism spectroscopy is widely used in the field of chemistry and biology to distinguish the enantiomers, which typically show either positive or severe side effects in biological applications depending on the molecular structures’ chirality. To effectively detect the chirality of molecules, diverse designs of nanostructured platforms are proposed based on optical resonances that can enhance the optical chirality and amplify the signal of circular dichroism. However, the underlying physics between the optical chirality and the resonance in a nanostructure is largely unexplored, and thus designing rules for optimal chiral detection is still elusive. Here, we carry out an in-depth analysis of chiral enhancement (C enhancement) in nanostructured surfaces to find the relationship between optical resonances and chirality. Based on the relations, we optimize the nanostructured metasurface to induce effective chiral detection of enantiomers for diverse conditions of molecule distribution. We believe that the proposed designing rules and physics pave the important pathway to enhance the optical chirality for effective circular dichroism spectroscopy.

Highlights

Chirality refers to the property that an object cannot be superimposed with its mirror image [1,2]
Chirality is an observable property in diverse molecules and plays a crucial role in determining the molecules’ chemical and biological properties, which are important in the fields of life science, analytical chemistry, biochemistry, and medicine [3,4,5,6]
The need for developing technology to distinguish such chiral molecules has been noticed since the discovery that the enantiomer of thalidomide, which was sold as an anti-morning drug in the 1950s, caused birth defects and malformed babies

Summary

Introduction

Chirality refers to the property that an object cannot be superimposed with its mirror image [1,2]. Achiral nanostructures exhibiting mirror symmetry are exploited, which amplify the optical chirality of orthogonally polarized incident light The former approach helps the researchers to elucidate the mechanism and how the CPL interact differently in chiral nanostructures [9,10,11,12,13]; the intrinsic chiral geometry in such nanostructure severely distorts and eludes the detection of the target molecules’ chirality, which is not appropriate for the CD spectroscopy. We design a set of metasurfaces for effective chiral detection in the diverse conditions of molecular distribution, i.e., located in local hotspots or the overall surface area

Theory and Simulation Methods

Results and Discussion

44.. Conclusions