Real-time MOF self assembly: Liquid electron view

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  • Published: Jun 15, 2015
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Real-time MOF self assembly: Liquid electron view

Dynamic view

The UC San Diego chemists observed the growth of complex organic-inorganic hybrid materials in real time, providing an unprecedented understanding of their formation. Credit: Joseph Patterson, UC San Diego

Liquid cell transmission electron microscopy has been used to visualize the growth of 'nanoscale' chemical complexes in real time by researchers at the University of California San Diego, Florida State University and Pacific Northwest National Laboratories. The work described in the Journal of the American Chemical Society could open up new approaches to nanoscience, perhaps allowing chemists and material scientists to develop step by step approaches to their craft in the nano realm.

Earlier investigations of nanostructures have tended to look at large-scale alterations of a bulk population of particles or using electron microscopy to grab a sequence of static snapshots of a given nanostructure and its behaviour.

"That process is like taking photos every 10 minutes of a football game and then trying to piece these photos together to tell the story of what is really a highly dynamic process," explains UCSD's Nathan Gianneschi, who led the research with Seth Cohen, also of UCSD. "Until now, this was the state of the art in terms of how we could document how nanostructures formed," he adds. "The development we describe in our paper demonstrates that these processes can be observed in real time, by literally videoing these processes on the nanoscale level using an electron microscope."

Transmission Electron Microscopy, TEM, has been used for many years, but the team employed a recently developed extension to this technique, Liquid Cell Transmission Electron Microscopy. LCTEM has been used previously to visualize the motion of nanoscale objects in liquids, but no team had reported a way to use it to visualize the growth of complex self-assembled, chemical nanostructures, until now.

Going for growth

"We showed for the first time that this technique can be used to observe the growth of complex organic-inorganic hybrid materials, providing an unprecedented understanding of their formation," explains Gianneschi. "This demonstration marks a significant step forward in LCTEM becoming essential for our understanding of nanoscale processes for all materials in liquids."

Colleagues included Joseph Patterson and Michael Denny of UCSD, PNNL's Patricia Abellan, Nigel Browning and James Evans and FSU's Chiwoo Park. Patterson and Evans undertook the actual LCTEM studies while Park was responsible for the video analysis. To make things simple, the researchers initially set out to study a chemical system known to assemble with a limited number of components and give rise to well-defined materials.


"We considered metal-organic frameworks [MOFs] to be the perfect starting point for this because they give ordered structures through an assembly process and include organic and inorganic components,” explains Gianneschi. The first step was to find out whether their nanostructures would actually survive the experiment itself. "This is necessary because materials are susceptible to being destroyed by the high energy electron beam that is used to image them," adds Gianneschi. Once the team had the right conditions for the experiments, they could then allow a solvent carrying their starting materials to flow into a liquid cell in the TEM instrument and watch as the materials underwent assembly.

This proof of principle bodes well for similar real time imaging experiments of other "delicate" self-assembly processes, such as the construction and folding of biological structures and even viruses.

"This advance provides a tool for observing material as they assemble with resolutions only possible using electron microscopy," Gianneschi adds. "That is, length scales can be observed that are relevant to nanoscale materials and processes. In terms of imaging dynamics like this, we believe it will impact how nanotechnology is developed in the future."

Related Links

J Am Chem Soc 2015, online: "Observing the Growth of Metal − Organic Frameworks by in Situ Liquid Cell Transmission Electron Microscopy"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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