The structural colors of the Blue butterflies: from sexual signaling to chemically selective vapor sensing

Day flying butterflies often use species-specific colors in sexual communication. Structural colors often can be found in polyommatine butterflies to accomplish this type of communication. The photonic nanoarchitectures of biological origin, for example in the wing scales of these butterflies, can be used as inexpensive sensor materials for vapor detection. These are nanocomposites of chitin and air, with structural elements typically 100 nm in size. The small dimensions of the air-filled pores facilitate the capillary condensation of the vapors into the nanostructure which results in the spectral shift of the structural color. In this work, we studied the photonic nanoarchitectures of the wing scales of blue polyommatine butterflies using different microscopic techniques and the optical properties of the generated structural color using spectrophotometry. It was shown that photonic nanoarchitectures and the structural colors of closely-related butterfly species living in the same habitat are species-specific. We applied the blue wings of polyommatine butterflies for optical vapor sensing. It was found that the spectral shift is vapor-specific and proportional with the vapor concentration. We showed that the conformal modification of the scale surface by ethanol pretreatment can significantly enhance the both optical response and the chemical selectivity.