A novel fabrication method that precisely controls the fabrication of 3D microstructures allows structural color to be produced at multiple wavelengths [Image: Colm Delaney, Trinity College Dublin and AMBER]
Some of the most dazzling displays in the natural world are created by structural color, where micrometer-scale surface structures create shifting patterns of brilliantly colored light. Now, researchers in Ireland have devised a single-step process for fabricating microstructures that can produce structural color of any visible wavelength (Adv. Mater., doi: 10.1002/adma.202504116). The technique enables multicolored images to be produced with high precision, opening up diverse applications in photonics, sensing and biomedical engineering.
Structural-color-producing microstructures
Previous research has shown that bright structural color can be produced by colloidal particles that spontaneously arrange themselves into three-dimensional lattices. However, the wavelength of the reflected light depends on the spacing between the particles in the self-assembled lattice, which is difficult to control and cannot be altered with any precision once the colloidal crystal has formed.
In this new work, the researchers combine direct laser writing with self-assembly to create intricate microstructures that can produce structural color across the visible range. Polymer nanoparticles are first dispersed in a solvent to create a colloidal crystal, which forms a film of photoresist when cooled in a glass cell. A focused laser beam then drives localized chemical reactions within the photoresist, allowing the fabrication of complex 3D structures with high fidelity.
The researchers believe that the technique could be adapted to work with different types of nanoparticles, which would make it possible to create color-changing sensors that respond to external stimuli such as light, temperature or magnetic fields.
In this dry state the microstructures exhibit no structural color, but once hydrated they reflect light across all visible wavelengths. Altering the fabrication parameters allowed the researchers to precisely control the spacing between the particles, with smaller separations shifting the reflected spectra toward lower wavelengths. Simulations of the 3D ordering within the microstructures confirm that the combined fabrication process enables the inter-particle spacing to be varied in all three dimensions, with the vertical separation between the lattice layers having most influence on the structural color.
Brilliant, programmable colors
As a proof of concept, the researchers programmed their direct laser writer to create a 3D microstructure of a hummingbird extracting nectar from a flower. By varying the fabrication parameters across the design, the team created a bright and multicolored representation of the scene. “We now have a way to fine-tune nanostructures to reflect brilliant, programmable colors,” said team leader Colm Delaney of Trinity College Dublin and AMBER (the Research Ireland Centre for Advanced Materials and Bioengineering Research).
The researchers believe that the technique could be adapted to work with different types of nanoparticles, which would make it possible to create color-changing sensors that respond to external stimuli such as light, temperature or magnetic fields. The team is now investigating whether such responsive devices could be used to track biochemical changes inside the body.