Inspired by the way the colorful feathers of colorful birds react with light, scientists have succeeded in creating thin layers of an innovative material in a variety of pure colors - from red to green - where the color is determined by the physical structure of the material and not by the chemical dyes inside it.
![Tiny bundles of melanin bound between keratin found in the feathers of this African starling react with light to produce the iridescent colors on its back. [Courtesy of Liliana D'Alba]](https://www.hayadan.org.il/images/content3/2015/06/nano-starling-15001-500x239.jpg)
Chemists have succeeded in synthesizing and isolating nanoparticles that are the synthetic version of melanin - the substance found in the natural structures of bird feathers and giving them their bright color. Basic color is obtained from the interrelationships between light and materials with structural patterns at the microscopic level, patterns that deflect and reflect the light rays while amplifying some of the wavelengths and omitting another part of them. Melanosomes, tiny packages of melanin found in the feathers, skin and fur of many species of bees, are able to produce structural color when compressed into solid layers, as seen in the feathers of birds.
"We synthesized and assembled nanoparticles of the synthetic version of melanin designed to mimic the natural structures found in bird feathers," said Nathan Gianneschi, professor of chemistry and biochemistry at the University of California, San Diego. "We wanted to understand how nature uses such materials and then develop new materials that will be more effective than those that exist in nature."
The researchers focused on nanoparticles capable of sensing the environment and reacting to it. The lead researcher came to this project after hearing a lecture from a biology professor about structural color in bird feathers. The research findings have long been published in the scientific journal ACS Nano.
In order to mimic the melanosomes, the researchers attached a similar molecule, dopamine, to a network structure. The resulting polymer, polydopamine, organized into spherical nanoparticles of uniform size. The researchers dried different concentrations from the particle solution to obtain thin layers of densely packed polydopamine particles. The layers reflected the light of pure colors: red, orange, yellow and green, with the hue determined by the thickness of the polydopamine layer and the degree of compactness of the packaging. The colors have an extraordinary uniformity throughout the entire layer, this according to exact measurements.
The properties of the material may contribute to its possible applications. Pure color is a valuable property in colorimetric (based on color change) detectors, and unlike dyes or dye-based dyes (pigments), structural colors do not fade over time. Polydopamine, like melanin, absorbs ultraviolet radiation, and therefore, coatings composed of this polymer will also be able to protect other materials from the radiation. Dopamine is also a biological molecule that is used to transmit information in the body, and therefore it can also be easily biodegradable.
"What fascinated me for 15 years was the idea that it is possible to produce shades in all the colors of the rainbow through minute changes (at the nanometer level) in the structure of the material," said the lead researcher. "This idea of biomimetics, i.e. imitating features from nature, is able to solve practical problems, but more than that, it also allows us to examine the mechanisms and results of theories we have developed," the researcher notes.
Natural melanosomes found in bird feathers vary in size and shape, and have rod and globule shapes that may be compressed or hollow. The researchers' next step is to change the shapes of the polydopamine nanoparticles in order to mimic this variety and to examine how the size and shape affect the interaction of the particle with light, that is, the color obtained from it. Ultimately, the researchers expect to produce a spectrum of biologically compatible structural colors.
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Tiny bundles of melanin bound between keratin found in the feathers of this African starling react with light to produce the iridescent colors on its back. [Courtesy of Liliana D'Alba]
One response
Dr. Nachmani, I'm sorry to write this, but such publications have been known for decades. Thus, for example, changes in the size of nanoparticles produce different colors, even for the exact same material (for example gold nanoparticles can be blue, red, etc.). The use of melanin is not new either. In conclusion, in this article the researchers simply repeated and described known phenomena in chemistry and biochemistry.