Humidity sensors mimicking cuticle of Hercules beetles

This paper reports a biomimetic humidity sensor inspired by the humidity-dependent color change observed in the cuticle of the Hercules beetle. A film-type humidity sensor with nanoporous structures based on 3D photonic crystals was designed and fabricated using the colloidal templating method and a surface treatment. The visible color of the fabricated humidity sensor changes from blue-green to red as the environmental humidity increases. The wavelength of reflected light that is predicted by Bragg´s equation considering the effect of water absorption shows a good agreement with experimental results.