Bio-inspired photonics

Molecular biomimetics involves the design of optical materials based on specific molecules and/or macromolecules to induce coloration.[1] Pigment-inspired materials aiming for specific molecular light absorption have been developed as for example melanin-inspired films prepared by polymerization of melanin precursors such as dopamine and 5,6-dihydroxyindole to provoke color saturation.[3][4][5] Materials based on the multi-layer stacking of guanine molecular crystals found in living organisms (e.g. fish[6] and chameleons[7]) have been proposed as potential reflective coatings and solar reflectors. Protein-based optical materials, for instance self-assembling reflectin proteins found in cephalopods [8][9] and silk,[10] have incited interest in artificial materials for camouflage systems,[11] electronic paper (e-paper)[12] and biomedical applications.[13] Non-protein biological macromolecules such as DNA have also been utilized for bio-inspired optics.[14] The most abundant biopolymer on earth, cellulose, has been also utilized as a principal component for bio-optics.[15][1] Modification of wood or other cellulose sources can mitigate scattering and absorption of light leading to optically interesting materials such as transparent wood and paper.[16][17]

Structural color is a type of coloration that arises from the interaction of light with nano-sized structures.[18] This interaction is possible because these photonic structures are of the same size as the wavelength of light. Through a mechanism of constructive and destructive interference, certain colors get amplified, while others diminish.

Photonic structures are abundant in nature, existing in a wide range of organisms. Different organisms use different structures, each with a different morphology designed to obtain the desired effect. Examples of this are the photonic crystal underlying the bright colors in peacock feathers[19] or the tree-like structures responsible for the bright blue in some Morpho butterflies.[20]

An example of bio-inspired photonics using structures is the so-called moth eye. Moths have a structure of ordered cylinders in their eyes that do not produce color, but instead reduce reflectivity.[21] This concept has led to creation of antireflective coatings.[22]