Biologically inspired humidity sensor based on three-dimensional photonic crystals

This letter presents a biomimetic humidity sensor inspired by the humidity-dependent color change observed in the cuticle of the Hercules beetle. A thin-film-type humidity sensor with nanoporous structures (three-dimensional photonic crystals) mimicking the spongy multilayer in the beetles was designed and fabricated using the colloidal templating method and a hydrophilic 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. (c) 2010 American Institute of Physics. [doi:10.1063/1.3486115]