With ever increasing technological advances, the demand for smart materials is always on the upswing. We define smart materials as those which can exhibit shape and appearance changes or self-heal upon wear and tear or damage. Importantly, if such materials can be made reusable and recyclable, this can lead to sustainability without losing the technological edge. For example, smart textiles that can change their color based on the temperature or windows that selectively allow light based on the environment.
Figure 1. Photo credit. Nature Communications, Michel C. Milinkovitch
To be able to create such technologies, scientists and engineers often look up to nature for inspiration. While human beings, do not have the ability to dynamically change their skin or hair color, nature, on the other hand, displays remarkable ability to showcase color changes. For example, certain animals like chameleons change their color based on the surroundings they are in, sea creatures like octopus can camouflage, (1) to attack prey or defend themselves from predators. The underlying process involves expansion and contraction of skin. Such natural phenomena have inspired material scientists to fabricate materials that can dynamically change colors in response to environmental stimuli.
In this Nanopinion, we aim to introduce our recent research work conducted at Aalto University in Finland, on adaptable materials. In particular, we wish to highlight through our work the need to bring together diverse set of materials to achieve cutting edge sustainable technological innovations.
In our quest to develop dynamic and adaptable materials, we investigated the use of gold nanoparticles, DNA molecules and polymers to create materials that adapt to light stimulus to generate colors. Gold (Au) as an element is particularly interesting for its ability to generate color when it is reduced into its nano form. The usage of gold to generate colors is not new, and it has been used since ancient roman times. Romans knew the art of coating glass with silver and gold metal to obtain vibrant colors. Moreover, gold can be easily recovered with existing recyclable methods. (2)
DNA has long been known as the genetic information carrier, and DNA based material fabrication technologies have been on the rise. DNA as a programmable element has revolutionized the way materials are built on the nanoscale. The inherent simplicity associated with its sequence and its responsiveness to salt and temperature makes DNA an excellent ingredient to build and modify materials. Finally, the use of water-soluble polymers, can aid in the recyclability of the materials.
Our strategy relied on bringing together diverse materials such as water-soluble polymers, gold nanoparticles and DNA molecules in a symbiotic manner to create materials that are responsive to mechanical and light stimuli. (3) To do this, we first attached two strands of DNA to gold nanorods with varying temperature responsive features. Here, gold nanorods are of the size that is equal to 1/10 thickness of a human hair. Next, we polymerized temperature responsive acrylamide-based polymers along with DNA attached gold nanorods, that led to the formation of a DNA engineered hydrogel with light adaptive color responses. In our design, gold nanorods are utilized as nano heaters and as color forming elements. When the hydrogel sample was illuminated with visible light, gold nanorods absorb the light and release the heat in the vicinity.
Figure 2. Photo credit, Advanced Functional Materials, Joonas Ryssy
The temperature rise leads to the melting of DNA strands thereby influencing the orientation of gold nanorods. The hydrogel transmits green or red light based on the orientation of gold nanorods mediated by DNA strands and it works nicely in the temperature range of 30°C – 70°C. Furthermore, the color responses are reversible and can be easily cycled multiple times. By bringing together a diverse set of materials, we thus demonstrated that color control can be easily achieved by simple visible light.
We are currently trying to extend the usage of these materials in developing three dimensional (3D) colors. 3D colors can provide compelling depth sensation to the viewer thereby providing an enhanced experience. (4) Our strategy involves using chiral nanoparticles templated by 3D engineered DNA structures. Chiral nanoparticle assemblies owing to their geometric configuration can result in the manipulation of light in three dimensions.
We believe that the science developed here is simple and relies on materials that are not toxic to living organisms and most importantly they can be easily recycled. We also anticipate that light-based control of colors can potentially spin-off applications in the domain of intelligent textiles that can change color based on the environment or smart windows that can transmit light selectively.
For example, a company by the name LLumar a polymer based films that can be attached to any glass surface, which lets only visible light to pass through and filtering out heat. This helps to keep the cool indoor spaces, potentially eliminating the use of air conditioners.
(1) Teyssier, J.; Saenko, S. V.; van der Marel, D.; Milinkovitch, M. C. Photonic Crystals Cause Active Colour Change in Chameleons. Nat Commun 2015, 6 (1), 6368.
(2) Gold Recycling – the Environmentally-Friendly Alternative | Gold.Info, 2013.
(3) Ryssy, J.; Lehtonen, A. J.; Loo, J.; Nguyen, M.-K.; Seitsonen, J.; Huang, Y.; Narasimhan, B. N.; Pokki, J.; Kuzyk, A.; Manuguri, S. DNA-Engineered Hydrogels with Light-Adaptive Plasmonic Responses. Advanced Functional Materials n/a (n/a), 2201249.
(4) Zhan, X.; Xu, F.-F.; Zhou, Z.; Yan, Y.; Yao, J.; Zhao, Y. S. 3D Laser Displays Based on Circularly Polarized Lasing from Cholesteric Liquid Crystal Arrays. Advanced Materials n/a (n/a), 2104418.
Sesha Manuguri is a postdoctoral researcher in the Molecular Nanoengineering group at the Department of Neuroscience and Biomedical Engineering, Aalto university. He completed his PhD in chemistry in 2020 from the University of Auckland (New Zealand). He is currently interested in developing nanocomposite materials for integrating functional optical structures towards fabricating ‘green’ devices for display applications.
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