Chameleons use nanocrystals to change colour

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  • Published: Mar 10, 2015
  • Author: Steve Down
  • Channels: UV/Vis Spectroscopy
thumbnail image: Chameleons use nanocrystals to change colour

Chameleons change colour by tuning a series of crystals in their skin, say scientists in Switzerland. Using a combination of histology, electron microscopy, photometry with an SLR camera and a video camera, supported by optical band gap calculations, Michel Milinkovitch and colleagues from the University of Geneva showed that the panther chameleon has a double layer of light-reflecting cells known as iridophores under its skin containing guanine nanocrystals of different size and shape and arrangement.

Writing in Nature Communications, the explained how the chameleon modifies the spacing between individual crystals in the upper layer to change the colour, as in photonic crystals. An increase in the distance results in a shift in reflectivity from short to long wavelengths, ie from blue to red or infrared. However, bearing in mind that the background skin colour is green containing yellow pigments, this results in a change of colour from green to orange-yellow.

The guanine crystals in the lower layer are larger, flatter and more disorganised than those in the upper layer and these probably act as thermal regulators for the animal, reflecting irradiation from the sun.

The two-layer organisation of the crystals "constitutes an evolutionary novelty for chameleons that allows some species to combine efficient camouflage with spectacular display," said the research team.

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