Inspired by the way iridescent bird feathers play with light, UC San Diego scientists have created thin-film materials in a wide range of pure colors: red, orange, yellow, and green. The hues are determined by physical structure rather than pigments.

Melanosomes, tiny packets of melanin found in the feathers, skin, and fur of many animals, can produce structural color when packed into solid layers, as they are in the feathers of some birds.

The UC San Diego researchers assembled synthetic melanin nanoparticles to mimic the natural structures found in bird feathers. Structural color arises from the interaction of light with the materials that have patterns on a minute scale, which bend and reflect light to amplify some wavelengths and dampen others.

To mimic natural melanosomes, Yiwen Li, a postdoctoral fellow in Gianneschi's lab, chemically linked a similar molecule, dopamine, into meshes. The linked polydopamine balled up into spherical particles of near uniform size. Researchers then dried different concentrations of the particles to form thin films of tightly packed polydopamine particles.

The films reflect pure colors of light. The hue is determined by the thickness of the polydopamine layer and how tightly the particles packed.

Unlike pigment-based paints or dyes, the structural color of the material does not fade. The UV-absorbing coating protects materials, and the pure hues could become a valuable trait in colorimetric sensors.

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