Integrating Cu₂O Colloidal Mie Resonators in Structurally Colored Butterfly Wings for Bio-Nanohybrid Photonic...

Colloidal Cu₂O nanoparticles can exhibit both photocatalytic activity under visible light illumination and resonant Mie scattering, but, for their practical application, they have to be immobilized on a substrate. Butterfly wings, with complex hierarchical photonic nanoarchitectures, constitute a promising substrate for the immobilization of nanoparticles and for the tuning of their optical properties. The native wax layer covering the wing scales of Polyommatus icarus butterflies was removed by simple ethanol pretreatment prior to the deposition of Cu₂O nanoparticles, which allowed reproducible deposition on the dorsal blue wing scale nanoarchitectures via drop casting. The samples were investigated by optical and electron microscopy, attenuated total reflectance infrared spectroscopy, UV-visible spectrophotometry, microspectrophotometry, and hyperspectral spectrophotometry. It was found that the Cu₂O nanoparticles integrated well into the photonic nanoarchitecture of the P. icarus wing scales, they exhibited Mie resonance on the glass slides, and the spectral signature of this resonance was absent on Si(100). A novel bio-nanohybrid photonic nanoarchitecture was produced in which the spectral properties of the butterfly wings were tuned by the Cu₂O nanoparticles and their backscattering due to the Mie resonance was suppressed despite the low refractive index of the chitinous substrate.