Mixtures of gold nanoparticles (yellow arrows) and other nanoscale crystals (blue arrows) in solution can be imaged by the new LCTEM technique. Images: Lucas Parent, UC San Diego.
Mixtures of gold nanoparticles (yellow arrows) and other nanoscale crystals (blue arrows) in solution can be imaged by the new LCTEM technique. Images: Lucas Parent, UC San Diego.

Chemists at the University of California, San Diego (UC San Diego) have developed a new tool that allows scientists to see for the first time ‘nanoscale’ mixing processes occurring in liquids. This means the tool can be used to study the progress of chemical reactions on nanomaterials and the development of nanoscale defects on the surfaces of materials.

"Being able to look at nanoscale chemical gradients and reactions as they take place is just such a fundamental tool in biology, chemistry and all of material science," said Nathan Gianneschi, a professor of chemistry and biochemistry, who headed the team. "With this new tool, we'll be able to look at the kinetics and dynamics of chemical interactions that we've never been able to see before." The research is described in a paper in Microscopy and Microanalysis.

Scientists have long relied on transmission electron microscopy (TEM) to see structures at the nanoscale. But this technique can take only static images and the samples must be dried or frozen and mounted within a vacuum chamber in order to be seen. This means that TEM can’t be used to view living processes or chemical reactions at the nanoscale. Examples include the growth and contraction within living cells of tiny fibers or nanoscale protrusions, which are essential for cell movement and division, or the changes caused by a chemical reaction in a liquid.

"As chemists, we could only really analyze the end products or bulk solution changes, or image at low resolution because we could never see events directly occur at the nanoscale," said Gianneschi.

The recent development of liquid cell TEM (LCTEM) has finally allowed scientists to take videos of nanoscale objects in liquids. But this technique is limited by its inability to control the mixing of solutions, which is essential when trying to view and analyze the impact of a drug on a living cell or the reaction of two chemicals.

Joseph Patterson, a postdoctoral researcher in Gianneschi’s laboratory, working with researchers at SCIENION in Germany and Pacific Northwest National Laboratory, has now taken a big step to resolving that problem. They have developed a technique and associated tool that allows scientists to deposit tiny amounts of liquid – about 50 trillionths of a liter – within the viewing area of an LCTEM microscope.

"With this technique, we can view multiple components mixed together at the nanoscale within liquids, so, for example, one could look at biological materials and perhaps see how they respond to a drug," said Gianneschi. "That was never possible before."

"The benefits to basic research are huge," he added. "We will now be able to directly see the growth at the nanoscale of all kinds of things, like natural fibers or microtubules. There's a lot of interest on the part of researchers in understanding how the surfaces of nanoparticles affect chemical reactions or how nanoscale defects on the surfaces of materials develop. We can finally look at the interfaces on nanostructures so that we can optimize the development of new kinds of catalysts, paints and suspensions."

While the scientists have not yet used their tool to view chemical reactions in solution, they have demonstrated that the technique can be used to image combinations of gold nanoparticles and other nanoscale crystals suspended in a liquid.

"What we've demonstrated is the proof of concept," said Gianneschi. "But that's what we'll be doing next."

Although this new tool won't allow scientists to actually view molecules in solution, Gianneschi said they should be able to see the impact of chemical reactions occurring on materials that are bigger than 5nm. "We won't be observing molecules colliding, but we will be able to observe single particles and collections of them on the nanometer length scale," he explained. "Observing these kinds of processes has been one of the key challenges in the field of nanoscience."

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