Light-emitting materials produced by the MIT team are shown under ultraviolet light, emitting different colors of light that can be modified by their environmental conditions. Image: Tara Fadenrecht.
Light-emitting materials produced by the MIT team are shown under ultraviolet light, emitting different colors of light that can be modified by their environmental conditions. Image: Tara Fadenrecht.

Researchers at the Massachusetts Institute of Technology (MIT) have developed a family of materials that can emit light of precisely controlled colors – even pure white light – and whose output can be tuned to respond to a wide variety of external conditions. This new material could prove useful for detecting specific chemical and biological compounds, or reporting mechanical and thermal conditions.

The material, a light-emitting lanthanide metallogel, can be chemically tuned to emit light in response to chemical, mechanical or thermal stimuli – potentially providing a visible output to indicate the presence of a particular substance or condition. It is described in a paper in the Journal of the American Chemical Society by assistant professor of materials science and engineering Niels Holten-Andersen, postdoc Pangkuan Chen, and graduate students Qiaochu Li and Scott Grindy.

The new material is inspired by nature. "My niche is biomimetics -- using nature's tricks to design bio-inspired polymers," Holten-Andersen explains. There are an amazing variety of "really funky" organisms in the oceans: "We've barely scratched the surface of trying to understand how they're put together, from a chemical and mechanical standpoint." Studying such natural materials, evolved over millions of years to adapt to challenging environmental conditions, "allows us as engineers to derive design principles" that can be applied to other kinds of materials, he adds.

Holten-Andersen's own research has involved examining a particular kind of chemical bond found in the threads used by mussels to anchor themselves to rocks. These bonds, known as metal-coordination bonds, also play an important role in many other biological functions, such as binding oxygen to hemoglobin in red blood cells.

The idea is not to copy natural materials, but to understand and apply some of the underlying design principles. In some cases, these principles can be applied to materials that are simpler in structure and easier to produce than their natural counterparts.

In this work, the use of a metal from the lanthanide group, also known as rare-earth elements, combined with a widely used polymer called polyethylene glycol (PEG) results in a material that produces tunable, multicolored light emissions. This light emission can reflect very subtle changes in the environment, providing a color-coded output that reveals details of those conditions.

"It's super-sensitive to external parameters," Holten-Andersen says. "Whatever you do will change the bond dynamics, which will change the color." So, for example, the materials could be engineered to detect specific pollutants, toxins or pathogens, with the results instantly visible just through color emission.

The material can also detect mechanical changes, and so could be used to detect stresses in mechanical systems, Holten-Andersen says. For example, it's difficult to measure forces in fluids, but this approach could provide a sensitive means of doing so. The material can be made as a gel, a thin film or a coating that could be applied to structures, allowing it to warn of a potential structural failure before it happens.

Metal-coordination bonds in polymers have been the subject of other work by Holten-Andersen. In a separate paper recently published in the journal Nature Materials, he reported making polymers with tunable mechanical properties, including stiffness. These materials are naturally self-assembling and self-healing and could be useful as energy-absorbing materials or in biological implants that need to be able to absorb impacts without breaking.

This story is adapted from material from MIT, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.