Inspired by nature, researchers at the Pacific Northwest National Laboratory (PNNL), along with collaborators at Washington State University, have created a new material capable of capturing light energy. This material provides a highly efficient artificial light collection system with potential applications in photovoltaics and bioimaging.
The research provides a basis for overcoming the difficult challenges involved in creating hierarchical functional organic-inorganic hybrid materials. Nature provides beautiful examples of hierarchically structured hybrid materials such as bones and teeth. These materials generally exhibit a precise atomic arrangement which enables them to achieve many exceptional properties, such as increased strength and toughness.
PNNL Materials Specialist Chun-Long Chen, corresponding author of this study, and his collaborators created a new material that reflects the structural and functional complexity of natural hybrid materials. This material combines the programmability of a synthetic protein-like molecule with the complexity of a silicate-based nanocluster to create a new class of very robust nanocrystals. They then programmed this 2D hybrid material to create a highly efficient artificial light collecting system.
“The sun is the most important source of energy we have,” Chen said. “We wanted to see if we could program our hybrid nanocrystals to harvest light energy – just as natural plants and photosynthetic bacteria can – while achieving the high toughness and processibility seen in synthetic systems. The results of this study were published on May 14, 2021 in Scientific progress.
Big dreams, tiny crystals
Although these types of hierarchically structured materials are exceptionally difficult to create, Chen’s multidisciplinary team of scientists combined their expert knowledge to synthesize a sequence-defined molecule capable of forming such an arrangement. The researchers created a modified protein-like structure, called a peptoid, and attached a precise cage-like structure made from silicate (abbreviated POSS) to one end of it. They then discovered that, under the right conditions, they could induce these molecules to self-assemble into perfectly formed crystals of 2D nanosheets. This created another layer of cell membrane-like complexity similar to that seen in natural hierarchical structures while maintaining the high stability and improved mechanical properties of individual molecules.
“As a materials scientist, nature provides me with a lot of inspiration,” Chen said. “Anytime I want to design a molecule to do something specific, like act as a drug delivery vehicle, I can almost always find a natural example to model my designs on.
Design bio-inspired materials
Once the team succeeded in creating these POSS-peptoid nanocrystals and demonstrated their unique properties, including high programmability, they then set out to exploit these properties. They programmed the hardware to include special functional groups at specific locations and at intermolecular distances. Because these nanocrystals combine the strength and stability of POSS with the variability of the peptoid building block, the programming possibilities were endless.
Once again looking for inspiration in nature, scientists have created a system capable of capturing light energy in much the same way as pigments found in plants. They added special “donor” molecule pairs and cage-like structures that could bind an “acceptor” molecule to specific locations in the nanocrystal. Donor molecules absorb light at a specific wavelength and transfer light energy to acceptor molecules. The acceptor molecules then emit light at a different wavelength. This newly created system exhibited an energy transfer efficiency of over 96%, making it one of the most efficient aqueous light collection systems of its type ever reported.
Demonstration of the uses of POSS peptoids for light harvesting
To demonstrate the use of this system, the researchers then inserted the nanocrystals into living human cells as a biocompatible probe for imaging living cells. When light of a certain color shines on cells and acceptor molecules are present, the cells emit light of a different color. When acceptor molecules are absent, the color change is not observed. Although the team has only demonstrated the usefulness of this system for imaging living cells so far, the improved properties and high programmability of this 2D hybrid material lead them to believe that it is the l one of the many applications.
“Although this research is still in its early stages, the unique structural characteristics and high energy transfer of 2D POSS-peptoid nanocrystals have the potential to be applied to many different systems, from photovoltaics to photocatalysis,” said Chen said. He and his colleagues will continue to explore the application routes of this new hybrid material.
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Material provided by DOE / Pacific Northwest National Laboratory. Original written by Sarah Wong. Note: Content can be changed for style and length.