Scientists unlock the light-bending secrets of squid skin

Squid are famous for flashing from glass-clear to kaleidoscopic in the blink of an eye, but biologists have long puzzled over the physical trick behind the act.

A research team led by the University of California, Irvine, joined by cephalopod experts at the Marine Biological Laboratory in Woods Hole, took that mystery head-on.

By peering into squid skin in three dimensions, they uncovered a hidden forest of nano-columns built from an uncommon protein called reflectin.

How squid skin bends light

These columns act much like tiny mirrors, bouncing or passing light depending on how close together they sit.

Alon Gorodetsky, an expert in chemical and biomolecular engineering at UC Irvine, is the senior author of the research.

“In nature, many animals use Bragg reflectors [which selectively transmit and reflect light at specific wavelengths] for structural coloration,” he said. “A squid’s ability to rapidly and reversibly transition from transparent to colored is remarkable.”

“We found that cells containing specialized subcellular columnar structures with sinusoidal refractive index distributions enable the squid to achieve such feats.”

Studying the master shapeshifter

The animals under study were longfin inshore squid, Doryteuthis pealeii. “These are longfin inshore squids – Doryteuthis pealeii – that are native to the Atlantic Ocean,” Gorodetsky said.

“Marine Biological Laboratory has been famous for studying this squid and other cephalopods for more than a century. We were fortunate to be able to leverage their world-class expertise with properly collecting, handling, and studying these biological specimens.”

Inside the squid mantle, shimmering cells known as iridophores – or iridocytes – hold the secret.

To visualize them without disturbing their delicate innards, the team used holotomography, a form of quantitative phase microscopy that maps how light bends through a sample.

Georgii Bogdanov, a postdoctoral researcher in chemical and biomolecular engineering at UC Irvine, is another lead author of the study.

“Holotomography used the high refractive index of reflectin proteins to reveal the presence of sinusoidal refractive index distributions within squid iridophore cells,” he said.

Reflectin platelets form spiral columns inside iridophores, enabling cephalopods to control how their skin transmits and reflects light.

Borrowing nature’s blueprint

Once the researchers understood the architecture – the stacked, spiraling Bragg reflectors – they wondered whether they could engineer something similar.

Studying squid color change inspired flexible materials that shift appearance using tiny, wavy Bragg reflector columns. They added nanostructured metal films, enabling the materials to also shift appearance in the infrared spectrum.

Using a mixture of polymer chemistry, nanofabrication, and metal coatings, the group built thin films that shift color when stretched, pressed, or heated.

They went a step further by tailoring the same films to tune their infrared emission. This allows the material to hide or reveal heat signatures as well as visible hues.

“These bioinspired materials go beyond simple static color control, as they can dynamically adjust both their appearances in the visible and infrared wavelengths in response to stimuli,” said co-author Aleksandra Strzelecka, a PhD student at UC Irvine.

“Part of what makes this technology truly exciting is its inherent scalability,” she said. “We have demonstrated large-area and arrayed composites that mimic and even go beyond the squid’s natural optical capabilities.”

This opens the door to many applications ranging from adaptive camouflage to responsive fabrics to multispectral displays to advanced sensors.

Future optics from squid skin

The implications stretch far beyond a novelty coating. The same Bragg-style stacks could sharpen laser output, filter signals in fiber-optic lines, and boost solar-cell efficiency. They could also enable real-time structural health monitoring in bridges and aircraft.

“This study is an exciting demonstration of the power of coupling basic and applied research,” Gorodetsky said. “We have likely just started to scratch the surface of what is possible for cephalopod-inspired tunable optical materials in our laboratory.”

Every advance stemmed from squid skin cells with tiny winding columns just hundreds of nanometers wide. Despite their size, these structures could orchestrate a light show visible from meters away.

The team’s work shows how decoding those natural nanostructures can lead to devices that humans manufacture by the meter rather than by the molecule.

Squid-inspired tech evolves

Researchers aim to speed up film response and develop biodegradable versions for sensors and medical patches.

Meanwhile, the discovery reaffirms why cephalopods remain a favorite subject for materials scientists: they are masters of manipulating light without a single pigment or battery.

In the lab, that mastery is starting to take shape as fabrics that cool soldiers in the desert by day, buildings that shimmer to reduce air-conditioning loads, and flexible screens that display both artwork and thermal data.

The next chapter, as Gorodetsky’s group sees it, will be written where biology and engineering merge.

The squid’s split-second shape-shifting trick has journeyed from the Atlantic deep to a microscope slide and into a polymer film.

Soon, it may appear on your jacket sleeve or smartphone case, blending vivid color with invisible infrared control just like in cephalopods.

The study is published in the journal Science.

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