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Iridescent photonic cellulose, which mimics the structural color of insects, with optical applications

A study developed at the ICMAB-CSIC and published in Nature Photonics describes the technique to provide structural coloration on a cellulose derivative through its nanostructuration. The colors obtained do not depend on pigments but on nanostructures that interact differently with the incident light. Applications include ecofriendly production of color in packaging systems or decorative paper, anti-counterfeiting technology, or biocompatible, biodegradable, washable and edible and low cost detectors, sensors or labels.

Sample of the photonic cellulose with structural colour (Agustín Mihi/ICMAB-CSIC).The bright colors of some butterflies, beetles or birds are not due to the presence of pigments that selectively absorb light, but due to the so-called structural coloration. Structural coloration occurs on surfaces with a nanostructure with dimensions similar to those of the wavelength of the incident light (typically below the micron).

These ordered nanostructures are known as photonic crystals. There is a great interest in providing cellulose, the most abundant polymer in earth, biocompatible and biogradable, with these structures, which can offer new optical and electric functionalities.

The study published today in Nature Photonics, led by Agustín Mihi, scientist of the Institute of Materials Science of Barcelona (ICMAB-CSIC), creates for the first time photonic crystals and plasmonic structures of a cellulose derivative through its nanostructuring with the soft lithography technique. By periodically nanostructuring the cellulose film, it is no longer transparent and begins to reflect intense colors, depending on the pattern with which it has been molded.

With this new, fully scalable and low cost technique, alternative to the traditional self-assembly of cellulose nanocrystals, a high quality and reproducible nanostructure is created on this polymer in a very short time, and achieving a wide range of iridescent colors, only depending on the size and morphology of the created structures.

These photonic crystals can be nanoimprinted on different substrates to provide photonic properties on surfaces that do not present this property, such as paper, demonstrating the potential of this technology as photonic ink, for applications in anti-counterfeiting technology, packaging, decorative paper, labels or sensors, among others.

With the new,  scalable and low cost technique, a high quality and reproducible nanostructure is created, with a

wide range of

iridiscent colors

When these structures are covered with a thin metal layer, they acquire plasmonic properties while maintaining their flexibility, achieving brighter colors. Furthermore, depending on the type of cellulose derivative used, its degree of biodegradability and solubility in water can be tuned. These plasmonic structures can be used as disposable sensors for Raman emission or to increase the light emitted by a dye.

Photonic crystals and plasmonic architectures are used in optics for their ability to manipulate light. In this work, these interesting optical properties are obtained in a biocompatible and biodegradable material, which can open up new fields of application. The study has been funded by the European Research Council (ERC Sarting Grant) through the the ENLIGHTMENT project, and by the Severo Ochoa project of the ICMAB.

Reference article:
Hydroxypropyl cellulose photonic architectures by soft nanoimprinting lithography. André Espinha, Camilla Dore, Cristiano Matricardi, Maria Isabel Alonso, Alejandro R. Goñi, and Agustín Mihi. Nature Photonics.