In a groundbreaking advancement that merges biology with cutting-edge materials science, researchers at the University of California, Irvine have unveiled the intricate structural mechanisms that allow squids to perform their mesmerizing rapid color transformations. This discovery opens new frontiers not only in understanding cephalopod biology but also in designing dynamic, multispectral materials inspired by nature’s engineering. By harnessing advanced three-dimensional imaging techniques, the team decoded how specialized skin cells modulate light to shift from transparency to a spectrum of iridescent hues—a process that until now eluded comprehensive scientific explanation.
Squids, particularly the longfin inshore species Doryteuthis pealeii, possess an extraordinary ability to transition their skin appearance fluidly and reversibly, cycling through transparent, blue, green, yellow, orange, and red states. Central to this phenomenon are iridophores—cells densely packed with stacked, undulating columns of platelets composed predominantly of a unique protein called reflectin. These platelet structures operate akin to natural Bragg reflectors. They manipulate light waves by reflecting and transmitting selective wavelengths, thereby engineering the squid’s dazzling display of structural colors in a highly tunable manner.
The investigative breakthrough came through the application of holotomography, a novel microscopy technique combining low-intensity light with quantitative phase imaging. This approach enabled the scientists to construct highly detailed 3D refractive index maps of the squid’s iridophores. Notably, holotomography illuminated subtle sinusoidal variations in the refractive index within the platelet columns, which are critical for the selective optical filtering properties of these cells. The sinusoidal modulation in refractive index is a unique optical design that provides precise control over reflected and transmitted light wavelengths, allowing squids to adapt their coloration for camouflage or communication.
Reflectin proteins organize themselves into complex, helical nanocolumns that fill the cellular interior of the iridophores. This intricate architecture underpins the squid’s aquatic camouflage abilities by enabling a dynamic interplay of light interference effects. Rather than relying on chemical pigments alone, these structural colors originate from physical manipulation of light itself, offering rapid reversibility and remarkable durability. Such fundamentally physical coloration mechanisms are distinct from traditional color production in animals and provide exceptional flexibility in situational appearance.
The team’s insight into the squid’s optical machinery led directly to the innovation of synthetic composites with tunable multispectral appearances. By mimicking the sinusoidal Bragg reflector architecture discovered in iridophore platelets, researchers engineered flexible, stretchable materials that can dynamically alter both visible spectrum colors and infrared signatures. This bioinspired design leverages nanocolumnar structures fabricated using advanced materials engineering techniques and integrates nanostructured metal films to extend responsive capabilities into infrared wavelengths, which are crucial for applications involving thermal stealth and multispectral detection.
Extensive microscopy and spectroscopic analyses validated that these engineered composites could perform a variety of complex optical functions. The materials demonstrate versatility for adaptive camouflage, signaling, and environmental sensing—capabilities vastly surpassing current static color technologies. These dynamic composites respond swiftly to mechanical deformation or environmental stimuli, adjusting their spectral reflectance in real time across multiple bandwidths. Such multifunctionality reveals the transformative potential for wearable technologies, responsive textiles, and next-generation optical devices.
One of the most exciting aspects of this research is its scalability. The materials developed can be produced in large-area arrays without compromising the uniformity or functionality of their optical properties. This paves the way for practical deployment in fields ranging from military stealth fabrics to colorimetric sensors and multispectral display systems. Unlike traditional pigment-based or dye-based coloration methods, these structurally tuned materials hold promise for long-term stability and environmental sustainability due to their physical rather than chemical color generation.
The scientific team credits access to the Marine Biological Laboratory at Woods Hole—an epicenter for cephalopod research—as instrumental in securing high-quality biological specimens essential for their detailed investigation. This collaboration brought together expertise in marine biology, chemical and biomolecular engineering, and advanced optics, underscoring the multidisciplinarity required to tackle such a complex biological phenomenon. The academic synergy facilitated comprehensive analyses from molecular scales up to whole tissue observations, bridging biology and materials innovation seamlessly.
Reflecting on the broader implications, the co-lead authors emphasized that their work represents an exemplary convergence of basic and applied research with potential to revolutionize photonic technologies. Fundamental insights into squid skin’s refractive index gradation could be extrapolated to enhance laser systems, fiber optic components, and photovoltaic devices by introducing tunable optical elements inspired by nature’s evolutionary solutions. This cross-pollination of biology and engineering heralds a new era of biomimetic materials whose design principles are rooted deeply in evolutionary mastery.
The profound ability of squids to fine-tune their appearance emerges from exquisitely orchestrated subcellular architectures rarely observed in other organisms. These internal columnar structures with sinusoidal refractive index profiles constitute an optical nanostructure of extraordinary precision and adaptability. Understanding and replicating these biological templates unlocks opportunities for creating artificial materials that are not only visually stunning but also functionally superior for multispectral manipulation.
Financing from the Defense Advanced Research Projects Agency (DARPA) and the Air Force Office of Scientific Research reflects the strategic importance of these discoveries, particularly in developing stealth materials and advanced sensors. The intersection of biological inspiration and materials science meets critical national interests by delivering novel optical devices with potential battlefield and civilian security applications. This funding support catalyzed the translation of squid biology into real-world technological innovations with practical deployment horizons.
Looking ahead, the research team envisions further exploration into tunable optical materials that leverage cephalopod-inspired designs. Continued advancements in nanoscale fabrication and compositional tuning hold promise for creating multispectral materials with programmable responses to complex external triggers. Such developments could redefine how humans interact with visual information, enabling adaptive environments and technologies that seamlessly blend into nature’s optical context.
The convergence of a biological marvel and human ingenuity demonstrated in this research heralds an exciting frontier where living systems inspire material platforms far beyond their original biological roles. Squid iridophores exemplify dynamic control over light that can be directly translated into scalable, multifunctional materials for a wide array of future applications. By deciphering and emulating these natural optical nanostructures, scientists are just beginning to unlock the vast design space nature perfected over millions of years.
Subject of Research: Cells
Article Title: Gradient refractive indices enable squid structural color and inspire multispectral materials
News Publication Date: 26-Jun-2025
Web References:
https://www.science.org/doi/10.1126/science.adn1570
References:
Science, Volume and issue as per publication date (details available via DOI)
Image Credits:
Alon Gorodetsky Lab, UC Irvine
Keywords:
squid, iridophores, reflectin, structural coloration, Bragg reflectors, holotomography, biomimetic materials, multispectral composites, dynamic camouflage, nanocolumnar structures, optical nanostructures, bioinspiration
