Uniform Chirality Enhanced Optical Responses via Broadband Achiral Metasurfaces for Bio-Sensing Applications

Due to the recent advancement in metamaterials for bio-sensing applications, metasurfaces are designed to enhance the chirality of the incident CP light by creating chiral hotspots formed by the interaction of electric and magnetic fields. Most of the reported works focus on induced chirality in plasmonic structures operated by shifting the molecules' circular dichroism (CD) signal to plasmonic resonance frequencies, which results in a decrease in efficiency. Moreover, chiral structures like gammadions were also reported, which can enhance the chirality. Still, the inherent chirality of the structure is much larger than the chirality of the molecules and thus overshadows it. Therefore, highly efficient planar nanomaterials with broadband uniform chirality are needed to sort and detect natural and artificially-made chiral molecules. This work presents an aluminum-based dimer structure that confines the central gap's chiral field, leading to highly uniform volumetric chirality enhancement. The proposed achiral dimer structure enhances the chirality of the incident circularly polarized light without interfering with the circular dichroism (CD) of the molecules. As a result, we report high volumetric chirality and dissymmetry factor compared to the state-of-the-art, which is the figures of merit for CD spectroscopy and separation of enantiomers, respectively. This work can be applied to distinguish molecules with CD bands in the ultraviolet and visible wavelengths.