POSS-peptoid molecules self-assemble into rhomboid-shaped nanocrystals. Image: Stephanie King/Pacific Northwest National Laboratory.
POSS-peptoid molecules self-assemble into rhomboid-shaped nanocrystals. Image: Stephanie King/Pacific Northwest National Laboratory.

Inspired by nature, researchers at Pacific Northwest National Laboratory (PNNL), along with collaborators at Washington State University, have created a novel material capable of capturing light energy. The material could form the basis of a highly efficient, artificial light-harvesting system with potential applications in photovoltaics and bioimaging.

This research provides a foundation 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 typically showcase a precise atomic arrangement that confers many exceptional properties, such as great strength and toughness.

PNNL materials scientist Chun-Long Chen 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 protein-like synthetic molecule with the complexity of a silicate-based nanocluster to create a new class of highly robust 2D nanocrystals. Chen and his collaborators programmed this 2D hybrid material to create a highly efficient artificial light-harvesting system.

"The Sun is the most important energy source we have," said Chen. "We wanted to see if we could program our hybrid nanocrystals to harvest light energy – much like natural plants and photosynthetic bacteria can – while achieving a high robustness and processibility seen in synthetic systems." Chen and his collaborators report their work in a paper in Science Advances.

Though 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 a structured arrangement. The researchers created an altered protein-like structure, called a peptoid, and attached a precise silicate-based cage-like structure (termed POSS) to one end of it.

Under the right conditions, they were able to induce these molecules to self-assemble into perfectly shaped crystals of 2D nanosheets. This created another layer of cell-membrane-like complexity similar to that seen in natural hierarchical structures while retaining the high stability and enhanced mechanical properties of the individual molecules.

"As a materials scientist, nature provides me with a lot of inspiration," said Chen. "Whenever I want to design a molecule to do something specific, such as act as a drug delivery vehicle, I can almost always find a natural example to model my designs after."

Once the team successfully created the POSS-peptoid nanocrystals and demonstrated their unique properties, including high programmability, they set out to exploit these properties by programming the material to include special functional groups at specific locations. Because these nanocrystals combine the strength and stability of POSS with the variability of the peptoid building block, the programming possibilities ae endless.

Once again looking to nature for inspiration, the scientists used their nanocrystals to create a system that could capture light energy much in the way the pigments in plants do. They added pairs of special 'donor' molecules and cage-like structures that could bind an 'acceptor' molecule at precise locations within the nanocrystal. The donor molecules absorb light at a specific wavelength and transfer the light energy to the acceptor molecules, which then emit light at a different wavelength. This newly created system displayed an energy transfer efficiency of over 96%, making it one of the most efficient aqueous light-harvesting systems of its kind reported thus far.

To showcase the use of this system, the researchers then inserted the nanocrystals into live human cells as a biocompatible probe for live-cell imaging. When light of a certain color shines on the cells and the acceptor molecules are present, the cells emit light of a different color. When the acceptor molecules are absent, the color change is not observed. Though the team has so far only demonstrated the usefulness of this system for live-cell imaging, the enhanced properties and high programmability of this 2D hybrid material leads them to believe this is just one of many applications.

"Though this research is still in its early stages, the unique structural features and high energy transfer of POSS-peptoid 2D nanocrystals have the potential to be applied to many different systems, from photovoltaics to photocatalysis," said Chen. He and his colleagues will continue to explore avenues for application of this new hybrid material.

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