Squid Magic? From Transparent to Rainbow - The Future of Light Unveiled by Squid's "Instant Transformation Cells"

1. Introduction: The Dress Code of the Deep Sea

Squids are particularly adept at "transforming" among marine creatures throughout history and across the globe. When sensing danger, they can become transparent in an instant, confusing predators. During communication with peers or courtship, waves of iridescent colors sweep across their skin, sending messages through color patterns. Behind the scenes, there are two types of coloration systems. One is the "chromatophore," which contains pigments like yellow, red, and black, and the other is the "iridophore," which uses light interference to produce color. This article delves into the latest research that has, for the first time in the world, unraveled the nanoscale structure hidden within iridophores in 3D, and based on these insights, a multifunctional photonic film was prototyped. We will also explore the reactions on social media.

2. Research Background: The Enigmatic Protein "Reflectin"

Inside iridophores, there is a high density of a special protein called "reflectin." Since its existence was reported in the 1950s, reflectin has been found only in certain cephalopods like squids, cuttlefish, and octopuses, making it a rare molecule. It possesses both positive and negative charges on its molecular surface, and its self-assembly state dynamically changes with phosphorylation and pH changes—this has been speculated to be involved in the mechanism of "instantaneous color change." However, how it actually forms a three-dimensional structure within cells and what physical laws it uses to manipulate light have long remained a "black box."

3. Approach: Capturing Cells in Their Entirety with 3D Holographic Tomography

In this study, a joint team from the University of California, Irvine (UCI) and Woods Hole Marine Biological Laboratory (MBL) adopted low-light quantitative phase microscopy (3D holographic tomography). This is a technology that can reconstruct internal structures at the nanoscale based on differences in refractive index, without the need for strong fluorescent dyes in live cells. The researchers extracted skin fragments from living California market squid (Doryteuthis pealeii) and acquired 3D datasets in just a few seconds per single volume. This allowed them to clearly understand how the "reflectin plates" are layered.

4. Discovery: Helically Layered "Movable Bragg Mirrors"

The analysis revealed that reflectin does not form plate-like structures but rather unprecedented structures where "nanocolumns" are stacked in a gentle helix. Each column is 200-400 nm wide, with an average pitch of 1.5 µm. The refractive index is high, with reflectin at 1.46 and water at 1.33, and this high contrast causes "Bragg reflection" through sinusoidal changes. When squids receive neural stimuli, the phosphorylation level of reflectin changes → the charge balance is disrupted → the osmotic pressure between columns changes → the distance between plates (d) contracts. The "d-value" can be reversibly varied in just a few milliseconds, shifting the reflection peak from the visible light range (blue to red) to the near-infrared range. It can truly be called a "movable Bragg mirror" created by living organisms.

5. Biomimetic Materialization: Films That Change Color and Infrared with Stretching

The intriguing aspect of this research is that it doesn't end with structural elucidation. The team mass-expressed the reflectin gene in E. coli, extracted the protein, and self-assembled it on a polyimide substrate to recreate nanocolumns. Additionally, they inserted ultra-thin metal layers of silver every 10 nm to provide infrared radiation control. The prototype film is 80 µm thick and flexible, showing a gradient change from green → orange → red when stretched, and reducing infrared emittance by up to 40% when the surface temperature is raised. Even after 2000 bending tests, the photonic properties were almost maintained.

6. Applications: Potential Expanding to Military, Environmental, and Medical Fields

Defense Camouflage
Since it can simultaneously control the three domains of visible light, near-infrared, and thermal radiation, it can achieve "color camouflage" and "thermal camouflage," which were previously covered by separate materials, with a single fabric. DARPA has already launched a pilot program, with field tests scheduled for 2027.

Wearable Temperature-Control Clothing
For outdoor workers and athletes, development is underway for "passive air-conditioning wear" that increases albedo and suppresses infrared radiation when temperatures rise, and conversely increases emissivity in cold conditions. Estimates suggest that it could reduce air conditioning energy use by 6-12% across entire cities.

Biological Sensors
Utilizing the property that the distance between reflectin columns changes with pressure and stretching, it can be used as a skin-adhered strain gauge to analyze blood pressure fluctuations and breathing patterns in real time. Being optical, it is less susceptible to electromagnetic noise.

Photonics Devices
Research has begun on applying variable Bragg reflection as resonant mirrors in microcavity lasers to construct maintenance-free tunable lasers. If coated inside optical fibers, "inline sensors" that change wavelength with external magnetic fields or temperature are also anticipated.

7. Social Media Reactions: "Science Fiction is Getting Closer to Reality"

As soon as the research was published in the U.S. journal Science, "#SquidSkinTech" trended on *X (formerly Twitter)*. A thread posted by tech influencer @The_Tradesman1 recorded 31,000 retweets and 12,000 likes in 48 hours. The comments ranged from jokes like "Elon Musk should stick this on Starship's outer wall" to concerns from the media world like "What will happen to reporting if optical camouflage uniforms become a reality?"

On Reddit's r/science, the top comment was a pun, "Reflectin? It's reflecting more than light; it's reflecting my insecurities about camouflage tech!" which received over 50,000 upvotes. In engineering-focused discussion threads, there were active deep discussions on implementation aspects, such as "How to increase throughput in roll-to-roll manufacturing processes" and "Can the self-assembly time be shortened from ms to µs?"

8. Expert Perspectives: The Intersection of Color Biology and Photonics

Associate Professor Leila Deravi from MIT Media Lab commented, "There are few precedents where animal coloration and materials science have come this close. The next step is to observe in real-time how chromatophores and iridophores coordinate in the nervous system to create dynamic patterns." Additionally, Professor Mario Aaron from Stanford University's Department of Applied Physics stated, "Reflectin, as a self-assembling polypeptide material, is sustainable without the need for rare metals. Combined with silicon photonics, it holds potential to function as an optical switch for next-generation data communication while significantly reducing CO₂ emissions."

9. Roadmap to Commercialization: Mass Production, Cost, and Regulation

In the current research prototype line, it is expensive at about $120 per square meter, but with funding from DARPA and the U.S. Air Force, a roll-to-roll production facility combining stencil printing + plasma polymerization is scheduled to be operational by the end of 2026. It is estimated that mass production could reduce the cost to $15/m² by 2028. On the regulatory side, since it contains biologically derived proteins, supply chain certification that clears biohazard levels is necessary. Additionally, export regulations (ITAR) may apply, and licenses and transparency are essential in domestic and international joint development.

10. Conclusion: The Future of Light Woven by the "Magic of the Sea"

Hidden in the skin of squids was a "movable Bragg mirror" akin to a living micromachine. The serendipity of basic science in animal behavior opens up a wide range of applications, from military camouflage and energy efficiency to medical sensors and even communication photonics. The survival technique of "instantaneous color change," evolved by marine organisms over tens of millions of years, may indeed provide a hint for the future for humanity facing climate crisis and resource depletion. Perhaps the next change will not be the color of squids, but our entire way of life.

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