Guanine-Based Photonic Crystals in Fish Scales Form from an Amorphous Precursor

摘要

A widespread material used by animals for producing structural colors is anhydrous guanine. A relatively well studied system is the anhydrous guanine crystal arrays that are responsible for the metallic luster of many fish, providing them with camouflage from a wide range of angles. Guanine may be the material of choice for this function because it is readily available in the cells as a nitrogenous metabolite, and anhydrous guanine has a very high refractive index, 1.83 in the reflecting direction. The fish control the crystal orientation and morphology, including forming the crystals as thin plates that expose the high refractive-index plane.