Self-assembly of amorphous biophotonic nanostructures by phase separation
- 30 March 2009
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Soft Matter
- Vol. 5 (9), 1792-1795
- https://doi.org/10.1039/b902775k
Abstract
Some of the most vivid colors in the animal kingdom are created not by pigments, but by wavelength-selective scattering of light from nanostructures. Here we investigate quasi-ordered nanostructures of avian feather barbs which produce vivid non-iridescent colors. These β-keratin and air nanostructures are found in two basic morphologies: tortuous channels and amorphous packings of spheres. Each class of nanostructure is isotropic and has a pronounced characteristic length scale of variation in composition. These local structural correlations lead to strong backscattering over a narrow range of optical frequencies and little variation with angle of incidence. Such optical properties play important roles in social and sexual communication. To be effective, birds need to precisely control the development of these nanoscale structures, yet little is known about how they grow. We hypothesize that multiple lineages of birds have convergently evolved to exploit phase separation and kinetic arrest to self-assemble spongy color-producing nanostructures in feather barbs. Observed avian nanostructures are strikingly similar to those self-assembled during the phase separation of fluid mixtures; the channel and sphere morphologies are characteristic of phase separation by spinodal decomposition and nucleation and growth, respectively. These unstable structures are locked-in by the kinetic arrest of the β-keratin matrix, likely through the entanglement or cross-linking of supermolecular β-keratin fibers. Using the power of self-assembly, birds can robustly realize a diverse range of nanoscopic morphologies with relatively small physical and chemical changes during feather development.Keywords
This publication has 14 references indexed in Scilit:
- Structural colours from the feathers of the birdBostrychia hagedashJournal of Physics D: Applied Physics, 2004
- Photonic structures in biologyNature, 2003
- A Fourier Tool for the Analysis of Coherent Light Scattering by Bio-Optical NanostructuresIntegrative and Comparative Biology, 2003
- Nano-Optics in the Biological World: Beetles, Butterflies, Birds, and MothsChemical Reviews, 1999
- Two-dimensional Fourier analysis of the spongy medullary keratin of structurally coloured feather barbsProceedings Of The Royal Society B-Biological Sciences, 1999
- Coherent light scattering by blue feather barbsNature, 1998
- Experimental modelling of exine self-assemblyBotanical Journal of the Linnean Society, 1996
- The role of self-assembly in biological systems: evidence from iridescent colloidal sporopollenin inSelaginellamegaspore wallsPhilosophical Transactions Of The Royal Society B-Biological Sciences, 1994
- Structure and development of iridescent butterfly scales: Lattices and laminaeJournal of Morphology, 1989
- Self-assembly of avian φ-keratinsProtein Journal, 1983