Biomimetic Bouligand Meta-Assembly Enhances Modulability of Chiroptical Cotton Effects

Hierarchical bioinspired nanostructures have garnered significant attention due to their ability to mimic natural phenomena in well-defined artificial systems. Specifically, bioinspired chiral metasurfaces demonstrate strong chiroptical interactions with circularly polarized light, setting the stage for their role in next-generation optical technologies. In this study, a nature-inspired approach mimicking the structure of the Protaetia scarab beetle exoskeleton was applied to fabricate Bouligand meta-assemblies of magnetoplasmonic gold/iron oxide nanowires. By sputter coating a thin metallic platinum layer with controlled thickness, the fabricated structure exhibits amplified and tunable circular dichroism (CD) in transmission, diffuse reflectance circular dichroism (DRCD), and magnetic circular dichroism (MCD) modes within the ultraviolet and visible wavelength range. A strong enhancement of bisignate Cotton effects in the transmission CD spectrum was observed by adding a 30-nm-thick platinum layer, while a thinner metallic coating layer of 10 nm provided the strongest enhancement effect in DRCD mode. Additionally, the MCD study and computational optical simulations revealed the unique interplay of plasmonic coupling, enhanced absorption/reflection, and conformal inheritance of chirality as the origin of the enhancement effect of the metallic coating layer. The facile biomimetic fabrication technique provides multimodal control of the chiroptical Cotton effects, holding promises for applications in structural coloration, camouflage photonics, anti-counterfeiting, chiral sensing, and asymmetric catalysis.