Differential SERS Enhancement Factors in Chiral Plasmonic Nanostructures

The surface-enhanced Raman scattering-chiral anisotropy (SERS-ChA) effect is a pioneering technique in enantioselective sensing, utilizing the enhanced Raman properties of chiral plasmonic nanostructures. This effect allows for highly sensitive and selective detection of chiral molecules, making it valuable for pharmaceuticals, environmental monitoring, and food safety, where distinguishing enantiomers is essential. However, systemic design rules for chiral plasmonic nanostructures that amplify their Raman signals based on chirality remain underexplored. In this study, we newly define the differential SERS-ChA enhancement factor (SERS-ChA EFs) by calculating the difference between SERS enhancement factors (EFs) under left- and right-circularly polarized light. By simulating the effects of various geometrical parameters of chiral plasmonic nanostructure arrays on their optical dissymmetry and differential SERS-ChA EFs, we provide critical insights for designing efficient SERS-ChA-based sensors. We modeled 3D chiral helicoid arrays with different sizes, intermolecular gaps, and materials under left and right circular polarized light extinction ports. By solving Maxwell's equations for finite element analysis, we calculated theoretical spectra for their chiroptical activities such as circular dichroism and their g-factors over a wavelength range of 400-800 nm while analyzing SERS-ChA EFs across different lines and surfaces to identify array regions with the highest enhancement effects. Our methods revealed varying minimum interparticle distances required to observe collective behavior and anisotropies in effective hot spots, based on helicoid size and material. Our findings advance theoretical frameworks for chiral effects in SERS and enhance the practical application of chiral metasurfaces in SERS-ChA spectroscopy, paving the way for advanced enantioselective sensing technologies.