Plasmonic Metasurfaces with Structural Chirality and Pseudo‐Chirality for Enhanced Circular Dichroism and Enantiomeric Recognition

Abstract The design and optical characterization of a plasmonic metasurface engineered to exhibit strong polarization anisotropy under both linearly and circularly polarized light is presented. The metasurface consists of geometrically asymmetric gold nanostructures arranged periodically on a glass substrate. Each nanostructure is formed by the fusion of three equilateral triangles. The nanostructures simultaneously break mirror and inversion symmetries, resulting in chiral and pseudo‐chiral optical responses that manifest as linear and circular polarization‐dependent spectral features. The numerical and experimental results reveal clear chiroptical effects in both near‐ and far‐field. Near‐field scanning optical microscopy confirms the excitation of polarization‐selective localized plasmonic modes, with spatially distinct hot‐spots lighting up under different incident polarizations. Furthermore, it is demonstrated that the metasurface exhibits a measurable enantiospecific optical response when coated with thin left‐ or right‐handed chiral overlayers. The differential circular dichroism signals observed in the presence of opposite enantiomers highlight the potential of the metasurface for label‐free chiral sensing. These findings provide new insights into the interplay between structural anisotropy, pseudo‐chirality, and enantioselective interactions in planar plasmonic systems, highlighting their ability to emulate chiral optical behavior without requiring volumetric 3D structures.