Ben-Gurion University-led research reveals how spiders produce a saturated blue-green color from imperfect nanoscale structures. The mechanism may aid in the development of sustainable structural dyes
How do animals in nature manage to produce bright, stable, and sometimes almost unfading colors, without relying on chemical dyes like those used in industry? New research led by Ben-Gurion University of the Negev offers a surprising answer: Spiders do not “overcome” the disorder in the tiny structures on their bodies, but rather use it in a controlled manner.
The study, published in the journal (PNAS), dealt with blue-tailed spiders and the optical mechanisms that allow them to produce saturated blue and green colors. The study was led by Prof. Ben Palmer from the Department of Chemistry at Ben-Gurion University and doctoral student Tali Lamkoff, in collaboration with researchers from the Weizmann Institute of Science, Lund University in Sweden, and Aalto University in Finland. (pnas.org)
Color that comes from structure, not color
Most of the colors we know from everyday life are created from pigments: substances that absorb some wavelengths and reflect others. In nature, there is another way – structural color. In this case, the color is created not because of a specific dye molecule, but because of the way light scatters, refracts and interferes in tiny nanometer-sized structures.
The problem is that such natural structures are not completely uniform. When the particles differ slightly in size or arrangement, the color can be weak, faded, or dependent on the viewing angle. This makes it especially difficult to get saturated color from structures that do not change much with angle. In the new study, the researchers showed that spiders solve the problem by using biological “photonic glass” – a collection of nanospheres that are not perfectly ordered, but optically well-aligned.
Two optical tricks of nature
The researchers identified two main mechanisms. The first is related to the relationship between the size of the nanoparticles and their refractive index. When the nanoparticles are larger, their refractive index is lower. Thus, even though the particles are not the same size, they reflect light in a way that produces a more consistent hue. In other words, the biological body compensates for the variation in size by changing the properties of the material.
The second mechanism is the incorporation of a yellow pigment into the semi-transparent spheres. The pigment does not “color” the sapphire in the usual sense, but rather filters out unwanted wavelengths and sharpens the reflection in the blue-green range. The result is a more saturated color, which does not depend only on light scattering but also on internal optical filtering.
The study also found that color changes during the maturation of the spider: young males appear greener, and mature males become more blue. This change is related to controlled changes in the size, density, and crystallinity of the nanoparticles in the pigment cells.
No more “green color” as a slogan
The importance of the finding is not that tomorrow the paint industry will replace all its coloring agents with superfine ones, but that the research reveals a biological engineering principle: it is possible to produce strong structural colors even from imperfect and even completely disordered systems. This is an important direction for the development of new optical materials, for example for paints, coatings, textiles, cosmetics, printing and anti-counterfeiting measures.
“Nature has found a remarkably elegant way to produce perfect colors using imperfect components,” said Prof. Palmer. He said the strategies revealed in the experiment could help in the future to produce efficient and sustainable optical materials, replacing some of the chemicals currently used in industry.
Lamkoff added that the mechanism could open a way to produce stable structural dyes that do not fade easily in the sun. However, this is a basic research stage: the path from superbug biology to commercial dyes is broad, and will require the development of appropriate materials and manufacturing processes.
The study also included Lotem Elus and Prof. Dan Oron from the Weizmann Institute of Science; Dr. Albert Batushansky, Yahel Fishman, Nila Theodore, Keshet Shavit and Lehav Heitner from Ben-Gurion University; Dr. Elmot Kalber from Lund University; and Dr. Johannes Haateja from Aalto University.
Short FAQ:
What is structural color? Color created by the interaction of light with tiny structures, not just from a chemical pigment.
What did the researchers discover? The spiders combine a change in the refractive index of nanoparticles with a yellow pigment that filters unwanted light.
why is it important? The mechanism may help develop stable and sustainable paints and coatings, if translated into industrial materials in the future.
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The sphaerit is a sphaerit, it's a shame about the incorrect literal translation from English when the animal's name appears in the Hebrew Language Academy, and even on Wikipedia. What's more, it's customary to state the scientific name.