3D tomographic analysis of the order-disorder interplay in the Pachyrhynchus congestus mirabilis weevil

TL;DR

This study combines 3D FIB tomography and simulations to analyze the nanostructures responsible for coloration in Pachyrhynchus weevils, revealing both ordered and disordered photonic structures that influence their vibrant colors.

Contribution

It demonstrates that blue scales have locally ordered diamond-like nanostructures capable of partial photonic bandgap formation despite overall disorder, advancing understanding of biological photonic materials.

Findings

Red scales have ordered diamond nanostructures.

Blue scales exhibit local order with disorder on larger scales.

Local order can produce photonic bandgaps at low dielectric contrast.

Abstract

The bright colors of Pachyrhynchus weevils originate from complex dielectric nanostructures within their elytral scales. In contrast to previous work exhibiting highly ordered single-network diamond-type photonic crystals, we here show by combining optical microscopy and spectroscopy measurements with 3D FIB tomography that the blue scales of P. congestus mirabilis differ from that of an ordered diamond structure. Through the use of FIB tomography on elytral scales filled with Pt by electron beam-assisted deposition, we reveal that the red scales of this weevil possess a periodic diamond structure, while the network morphology of the blue scales exhibit diamond morphology only on the single scattering unit level with disorder on longer length scales. Full wave simulations performed on the reconstructed volumes indicate that this local order is sufficient to open a partial photonic bandgap even at low dielectric constant contrast between chitin and air in the absence of long-range or translational order. The observation of disordered and ordered photonic crystals within a single organism opens up interesting questions on the cellular origin of coloration and studies on bio-inspired replication of angle-independent colors.