By placing squid pigments into a photovoltaic cell, researchers revealed the animals' incredible color-matching ability may be solar powered.
The dazzling shift of cephalopod colors, including those from octopus, cuttlefish, and squid, allow them to blend into their environments or visually communicate with each other. While researchers have long known pigment-filled chromatophores in their skin are involved in this process, we still do not fully understand how it works.
So biochemist Taehwan Kim and colleagues at Northeastern University in the US built a solar cell to see if the pigment granules inside the chromatophores from the longfin inshore squid (Doryteuthis pealeii) could facilitate the conversion of light into electricity.
Sure enough, on exposure to sunlight, the granules transferred a charge.
"We found that the more granules you put into there, the higher the photocurrent response is," Northeastern University biochemist Leila Deravi told Cody Mello-Klein at Northeastern Global News.
"It's a direct indication that the pieces of the chromatophore are actually converting the light from the sun-simulated light to the voltage, which can complete the circuit and then be harvested, potentially, for a power supply in the animal."
What's more, this system must be incredibly efficient, the researchers note, given squid can use this energy to change the appearance of their entire body under water where only low levels of light can reach.
"To have something sense the colors around it and distribute [them] within hundreds of milliseconds is really insane," says Deravi. "It's not something that's easy to do, especially in a living system that's under water."
Chromatophores, located across the skin of clever cephalopods, are filled with different colored pigments including red, yellow, and brown in the longfin inshore squid. This short-lived, planktonic feeder migrates across the North Atlantic, moving offshore in winters and back towards land as the waters warm, relying on their ink and camouflage to avoid their many predators from dolphins to flounder.
Each of their tiny pigment organs has nerves that can carry enough charge to cause the chromatophore muscles to contract and expand the organ up to 10 times its size, in synchrony with those around it. This allows them to create changing patterns of color.
"The remarkable large-scale resonance of chromatophores suggests electrical communication between chromatocytes," the researchers point out.
When exposed to light, the pigments release an electron in a redox reaction, creating a charge. This light 'sensing' signal may then spread to adjacent chromatophores, Kim and team suspect, possibly explaining how they can then synchronously shift pigment intensities to mimic the squid's surroundings.
Understanding more about these hyper-efficient light sensors could revolutionize fields like wearable electronics.
This research was published in the Journal of Materials Chemistry C.