Scientists at Harvard University and the Marine Biological Laboratory (MBL) hope a new understanding of a natural nanoscale photonic device that enables a small marine animal to change its colors will also inspire cosmetic applications.
In a paper published this week in the Journal of the Royal Society Interface, the Harvard-MBL team reports new details on the sophisticated biomolecular nanophotonic system, specifically in regards to the underlying color-changing ways in cuttlefish.
Cuttlefish, known as the "chameleon of the sea," can rapidly alter both the color and pattern of its' skin, helping it to blend in with its surroundings and avoid predators.
According to Kevin Kit Parker, Harvard Professor of Bioengineering and Applied Physics, deciphering the relative roles of pigments and reflectors in the fish's skin with this device is a key step to translating the principles of actuation to materials science and engineering.
"This project expanded our breadth of inquiry and uncovered several useful surprises, such as the tether system that connects the individual pigment granules and now the challenge is to reverse-engineer this system in a cost-efficient, synthetic system that is amenable to other applications," he explains.
The device allows scientists to determine pigment granules
The cuttlefish's controlled, pigmented organs called chromatophores allow it to change its appearance in response to visual clues, but scientists have had an incomplete understanding of the biological, chemical, and optical functions that make this adaptive coloration possible.
The scientists showed that within the chromatophore, tethered pigment granules regulate light through absorbance, reflection, and fluorescence, in effect functioning as nanoscale photonic elements, even as the chromatophore changes in size.
To regulate its color, the fish relies on a vertically arranged assembly of three optical components: the leucophore, a near-perfect light scatterer that reflects light uniformly over the entire visible spectrum; the iridophore, a reflector comprising a stack of thin films; and the chromatophore.
This layering enables the skin of the animal to selectively absorb or reflect light of different colors, says co-author Leila F. Deravi, a research associate in bioengineering at Harvard SEAS.
"Chromatophores were previously considered to be pigmentary organs that acted simply as selective color filters,” Deravi said. “But our results suggest that they play a more complex role; they contain luminescent protein nanostructures that enable the cuttlefish to make quick and elaborate changes in its skin pigmentation."