Carminic Acid Based Red Dye from Scale Insects Detected in Red Ruby-Crowned Kinglet Feathers by Surface-Enhanced Raman Scattering.

In most birds, red feather color is linked to diet and attributed to carotenoids contained in plants and fruits. In the red crown feathers of the Ruby-crowned Kinglet (Regulus calendula), a new biopigment was identified based on carminic acid, the main coloring compound of cochineal (Dactylopius coccus) and other scale insects. This has revealed a potential new class of carminic acid-based biopigments, not previously identified in feathers. In this research, red crown feathers of a Ruby-crowned Kinglet were analyzed by surface-enhanced Raman scattering (SERS) employing synthesized silver star-shaped colloids as the nanoplasmonic platform. Results indicated peaks at 450, 670, 1290-1312, 1355, 1410, 1570, 1620 cm in the feather SERS spectra characteristic of carminic acid. SERS has proven to be an extremely sensitive, non-destructive technique for the identification of different feather biopigments, even at trace quantities and in the presence of other predominant coloring substances.