Study on the chirality of gyroid photonic crystals in butterfly wing scales.

Some brilliantly colored butterflies are known to possess gyroid photonic crystals in the wing scale. As the gyroid structure is inherently chiral, it is an intriguing question whether the structure has enantiomeric purity or not, considering that biomolecules exhibit homochirality. It has been previously reported for a few lycaenid species that both enantiomeric forms of the gyroid structure are found in multidomain photonic crystals. In this study, we evaluated the chirality of gyroid crystals in the wing scales of the papilionid butterfly Teinopalpus imperialis and found only one enantiomeric form (LH-type) in more than 200 gyroid crystals examined. In another papilionid butterfly, Parides sesostris, the populations of the two enantiomeric forms were found to be highly unbalanced. Because the gyroid crystals of these two butterflies are known to have a strong orientation preference along the surface normal of the scale, we suggest that crystal orientation-controlled development is related to chirality selection. Our findings provide insights into chirality-selected gyroid synthesis in self-organization processes.