Surface-Enhanced Circular Dichroism by Localized Superchiral Hotspots in a Dielectric Dimer Array Metasurface

Circular dichroism (CD) spectroscopy is an important technique in the fields of chemistry, biology, and life sciences and is a commonly used method to analyze the chirality of molecules. However, due to the weak chirality of natural materials, CD signals are usually very small; hence, high sample density is normally required. Here, we theoretically proposed the generation of superchiral light–matter interaction on a high-refractive-index dielectric metasurface, which consists of silicon nanocylinder dimer structures. Upon the illumination of off-axial linear polarization, the interplay of enhanced E- and H-fields gives rise to the generation of a superchiral localized hotspot in the gap of the dimer. By introducing chiral molecules into the gap region, the CD signals of the system can be enhanced significantly. The origin of the enhanced CD is attributed to the inherent CD signals of the chiral molecules, and the background absorption is negligible. By patterning an array of silicon nanocylinder dimers in a square lattice, the volume-averaged chirality of the localized hotspot can be further increased up to 180-fold, leading to an improved CD enhancement factor of 120-fold. Our findings could provide a scalable and miniaturized platform for broad applications in CD spectroscopy, enantioselective sensing, sorting, synthesis, and photolysis.