Nanostructures in Nature

Nanostructures – objects with nanometer scale features – are not new nor were they first created by man. There are many examples of nanostructures in nature in the way that plants and animals have evolved.

On the surface of a butterfly’s wings are multilayer nanoscale patterns. These structures filter light and reflect mostly one wavelength, so we see a single bright colour. For instance the wings of the male Morpho Rhetenor appear bright blue. But the wing material is not, in fact, blue; it just appears blue because of particular nanostructures on the surface. The nanostructures on the butterfly’s wings are about the same size as the wavelength of visible light and because of the multiple layers in these structures optical interferences are created. There is constructive interference for a given wavelength (around 450nm for the Morpho Rhetenor) and destructive interferences for the other wavelengths, so we see a very bright blue colour. In the laboratory, many scientific instruments use this same phenomena to analyze the colour of light.

A moth’s eye has very small bumps on its surface. They have a hexagonal shape and are a few hundred nanometers tall and apart. Because these patterns are smaller than the wavelength of visible light (350-800nm), the eye surface has a very low reflectance for the visible light so the moth’s eye can absorb more light. The moth can see much better than humans in dim or dark conditions because these nanostructures absorb light very efficiently. In the lab, scientists have used similar man-made nanostructures to enhance the absorption of infra-red light (heat) in a type of power source (a thermo-voltaic cell) to make them more efficient!

The edelweiss (Leontopodium nivale) is an alpine flower which lives at high altitudes, up to 3000m / 10,000 ft, where UV radiation is strong. The flowers are covered with thin hollow filaments that have nanoscale structures (100-200nm) on their periphery. They will absorb ultraviolet light, which wavelength is around the same dimension as the filaments, but reflect all visible light. This explains the white colour of the flower. Because the layer of filaments absorbs UV light, it also protects the flower’s cells from possible damage due to this high-energy radiation.

(From www.nnin.org)