Brilliant biophotonics:physical properties, pigmentary tuning & biological implications

Fonkelende kleuren van vogels, kevers en vlinders onderzocht Miljoenen jaren van evolutionaire geschiedenis hebben tot de verbazingwekkende diversiteit van biologische organismen geleid, die tegenwoordig gebruik maken van verschillende kleurmechanismen om heldere, fonkelende kleuren te reflecteren. De meest briljante en schitterende kleuren, zoals het witste wit en het zwartste zwart van vele dier- soorten, zoals vogels, kevers en vlinders, ontstaan uit de fysieke interactie van licht met geordende, quasi-geordende en ongeordende materie, wat resulteert in structurele kleuren. Deze biofotonische nanostructuren kunnen variëren in complexiteit, gaande van 'eenvoudige' multilaag-structuren tot topologisch complexe, driedimensionale fotonische kristallen. Deze fotonische structuren veranderen de spectrale samenstelling van het invallende licht en creëren zo de fonkelende kleuren, die we iedere dag kunnen zien. Bodo Wilts onderzocht een waaier van fotonische structuren in vogels, kevers en vlinders en bekeek in detail hoe deze complexe structuren met het invallend licht wisselwerken. Hij bestudeerde hoe deze structuurkleuren afgestemd kunnen worden door de aanwezigheid van absorberende pigmentaire filters. Door een brede reeks van verschillende fysische technieken en rekenfysica te gebruiken, kreeg hij inzicht in de optische eigenschappen van deze complex gevormde composieten van structurele en pigmentaire kleuren. De biologische functies van deze structuren worden in het proefschrift besproken en kunnen variëren van interseksuele signalering tot camouflage

Living Light 2018: Conference Report

Living Light is a biennial conference focused on all aspects of light–matter interaction in biological organisms with a broad, interdisciplinary outlook. The 2018 edition was held at the Møller Centre in Cambridge, UK, from April 11th to April 14th, 2018. Living Light’s main goal is to bring together researchers from different backgrounds (e.g., biologists, physicists and engineers) in order to discuss the current state of the field and sparkle new collaborations and new interdisciplinary projects. With over 90 national and international attendees, the 2018 edition of the conference was strongly multidisciplinary: oral and poster presentations encompassed a wide range of topics ranging from the evolution and development of structural colors in living organisms and their genetic manipulation to the study of fossil photonic structures.S.V. thanks the Biotechnology and Biological Sciences Research Council (BBSRC) David Phillips fellowship (BB/K014617/1), the European Research Council (ERC-2014-STG H2020 639088), and the European Commission (Marie Curie Fellowship Looking Through Disorder (LODIS), 701455) for financial support. B.D.W. was financially supported through the National Center of Competence in Research Bio-Inspired Materials and the Ambizione program of the Swiss National Science Foundation (168223)

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

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.Comment: 13 pages, 10 figure

Ultra-dense, curved, grating optics determines peacock spider coloration

Controlling light through photonic nanostructures is important for everyday optical components, from spectrometers to data storage and readout. In nature, nanostructured materials produce wavelength-dependent colors that are key for visual communication across animals. Here, we investigate two Australian peacock spiders, which court females in complex dances with either iridescent color patterns (Maratus robinsoni) or an approximately angle-independent blue coloration (M. nigromaculatus). Using light microscopy, FIB-SEM imaging, imaging scatterometry, and optical modeling, we show that both color displays originate from nanogratings on structured 3D surfaces. The difference in angle-dependency of the coloration results from a combination of the local scale shape and the nanograting period. The iridescence of M. robinsoni arises from ordered gratings on locally flat substrates, while the more stable blue colors of M. nigromaculatus originate from ultra-dense, curved gratings with multiscale disorder. Our results shed light on the design principle of the peacock spiders' scales and could inspire novel dispersive components, e.g. used in spectroscopic applications

Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer

The iridescent plumage of many birds is structurally colored due to an orderly arrangement of melanosomes in their feather barbules. Here, we investigated the blue- to purple-colored feathers of the European starling (Sturnus vulgaris) and the blue and green feathers of the Cape starling (Lamprotornis nitens). In both cases, the barbules contain essentially a single layer of melanosomes, but in S. vulgaris they are solid and rod-shaped, and in L. nitens they are hollow and rod- as well as platelet-shaped. We analyzed the coloration of the feathers by applying imaging scatterometry, bifurcated-probe- and micro-spectrophotometry. The reflectance spectra of the feathers of the European starling showed multiple peaks and a distinct, single peak for the Cape starling feathers. Assuming that the barbules of the two starling species contain a simple multilayer, consisting locally only of a cortex plus a single layer of melanosomes, we interpret the experimental data by applying effective-medium-multilayer modeling. The optical modeling provides quantitative insight into the function of the keratin cortex thickness, being the principal factor to determine the peak wavelength of the reflectance bands; the melanosome layer only plays a minor role. The air cavity in the hollow melanosomes of the Cape starling creates a strongly enhanced refractive index contrast, thus very effectively causing a high reflectance

A literal elytral rainbow: tunable structural colors using single diamond biophotonic crystals in Pachyrrhynchus congestus weevils

The brilliant colors of many insects arise from the interference of incident light with complex nanostructured biomaterials that are present in their cuticle. Here, the rainbow‐colored spots on the elytra of a snout weevil, Pachyrrhynchus congestus pavonius (Coleoptera: Curculionidae), are investigated using synchrotron small‐angle X‐ray scattering, scanning electron microscopy, microspectrophotometry, and photonic bandgap modeling. It is shown that the iridescent scales present in the rainbow‐hued spots are due to a 3D photonic crystal network of chitin in air with a single diamond (Fd‐3m) symmetry. In many insects, different orientations of photonic crystal domains are used to create various hues. In this weevil, however, both the chitin volume fractions as well as the lattice parameters of the biologically self‐assembled single diamond nanostructure are varied to achieve the remarkable tuning of the structural colors across the visible light spectrum on a scale‐by‐scale basis. Uncovering the precise mechanism of color tuning employed by this weevil has important implications for further structural and developmental research on biophotonic nanostructures and may provide fresh impetus for bioinspired and biomimetic multifunctional applications, as synthesis of photonic crystals at visible length scales is currently challenging

Swelling and Softening of the Cowpea Chlorotic Mottle Virus in Response to pH Shifts

AbstractCowpea chlorotic mottle virus (CCMV) forms highly elastic icosahedral protein capsids that undergo a characteristic swelling transition when the pH is raised from 5 to 7. Here, we performed nano-indentation experiments using an atomic force microscope to track capsid swelling and measure the shells’ Young’s modulus at the same time. When we chelated Ca2+ ions and raised the pH, we observed a gradual swelling of the RNA-filled capsids accompanied by a softening of the shell. Control experiments with empty wild-type virus and a salt-stable mutant revealed that the softening was not strictly coupled to the swelling of the protein shells. Our data suggest that a pH increase and Ca2+ chelation lead primarily to a loosening of contacts within the protein shell, resulting in a softening of the capsid. This appears to render the shell metastable and make swelling possible when repulsive forces among the capsid proteins become large enough, which is known to be followed by capsid disassembly at even higher pH. Thus, softening and swelling are likely to play a role during inoculation