Have you ever wondered how a peacock's tail shimmers with brilliant blues and greens, or why a butterfly's wings flash colors that never fade? These are not paints or dyes, but "structural colors" — hues created entirely by microscopic structures that trap, bend and scatter light.

For years, scientists have tried to copy nature's approach to create vivid, long-lasting colors for uses that range from anti-counterfeiting labels to flexible displays. Now, researchers have taken a major step forward by developing a new type of optical metamaterial that gives them more precise control over microscopic structures, along with a production method that is as fast and inexpensive as printing a newspaper. Their findings were published in the journal Nature on April 22.

An optical metamaterial is a man-made material engineered to control light in unusual ways. Instead of relying on the natural properties of ordinary materials, scientists build tiny patterns smaller than a human hair that can bend, reflect and guide light with extreme precision.

One important use is structural coloration, whereby microscopic patterns create colors without pigments or dyes. The technology could lead to fade-resistant paints, secure holograms and energy-efficient displays. Scientists also see optical metamaterials as an important technology for future advances in optics, communications, high-end manufacturing and defense.

However, most earlier studies focused on structures built at only one scale, limiting scientists' ability to control light. Manufacturing also depended on highly specialized, but slow and expensive equipment. As a result, producing a sample as small as a fingernail could take days, keeping the technology largely confined to laboratories.

Now, a research team from the Chinese Academy of Sciences and the National University of Singapore says it has overcome the longstanding challenge of balancing quality, customization and low cost.

The team designed a new multiscale structure made of tiny dome-shaped surfaces combined with nanoscale crystal-like patterns. The researchers likened the design to a symphony orchestra, where different parts work together to control different properties of light. This gives scientists a multitude of ways to fine-tune how light behaves.

The researchers also developed a roll-to-roll nanoprinting system. It works much like newspaper printing: a flexible plastic sheet moves continuously through a high-precision printer that stamps nanoscale patterns onto the surface before rolling up as a finished product.

Using the method, the team expanded production from millimeter-sized test samples to sheets measuring meters wide — a thousandfold increase — without sacrificing quality.

Reviewers at Nature praised the breakthrough, saying the printing strategy is both novel and attractive.

Song Yanlin, the study's corresponding author and researcher at the Chinese Academy of Sciences' Institute of Chemistry, said the work combines materials science, optics and advanced manufacturing.

"Our roll-to-roll nanoprinting technology makes producing optical metamaterials as simple and efficient as printing a newspaper or a book," Song said. "It not only lowers costs and improves production efficiency, but also allows us to customize the optical properties of each metamaterial pixel on demand, opening new possibilities for micronano optics research."

Li Kaixuan, the study's first author and a doctoral graduate of the Institute of Chemistry, said a metamaterial film measuring 1 meter long and 30 centimeters wide can be printed in just 10 minutes. The process requires only 1 milliliter of a special nanoparticle ink, costing no more than 10 yuan ($1.5) per ml.

Li also highlighted the technology's broad potential applications. These include highly sensitive biosensors that can strengthen optical signals from viruses, helping detect infections that are otherwise difficult to identify, as well as photonic chips for VR and AR devices that could improve data transmission efficiency.

limenghan@chinadaily.com.cn