A recent study reveals a method to observe how nanoscale building blocks can be rearranged into various organized formations on demand. This innovative approach integrates an electron microscope, a specialized sample holder with tiny channels, and computer simulations. The research was conducted by teams from the University of Michigan and Indiana University.
Recent advancements allow us to explore how nanoscale building blocks can be rearranged into different organized structures on command, thanks to an approach that combines an electron microscope, a miniature sample holder with microscale channels, and computer simulations, as indicated by a new study conducted by researchers at the University of Michigan and Indiana University.
This method has the potential to create smart materials and coatings that can switch between various optical, mechanical, and electronic properties.
“One of my favorite natural examples is chameleons,” explained Tobias Dwyer, a doctoral student in chemical engineering at U-M and co-first author of the study published in Nature Chemical Engineering. “Chameleons alter their color by changing the spacing of nanocrystals in their skin. Our goal is to create a dynamic and multifunctional system that mimics some remarkable biological examples.”
The imaging technology provides researchers with a real-time view of how nanoparticles respond to environmental changes, offering a unique insight into their assembly behavior.
In their experiment, the Indiana team first suspended nanoparticles—tiny materials smaller than most bacteria—in microchannels filled with liquid on a microfluidic flow cell. This device enabled researchers to flush different fluids into the chamber while observing the mixture under an electron microscope. They discovered that the instrument provided the nanoparticles—typically attracted to one another—with just enough electrostatic repulsion to create ordered assemblies.
The nanoparticles, which consist of gold cubes, either aligned neatly in a structured cluster or formed a more chaotic arrangement. The final organization of the material depended on the properties of the liquid they were suspended in, and introducing new liquids into the flow cell prompted the nanoblocks to switch between these two configurations.
This experiment demonstrated a proof of concept for directing nanoparticles into specific structures. Although nanoparticles are too small for manual manipulation, this method could guide engineers in reconfiguring other nanoparticles by adjusting their surroundings.
“While it’s possible to transfer particles into different liquids, observing their responses to the new environment in real time was not feasible before,” said Xingchen Ye, an associate professor of chemistry at IU, who developed the experimental technique and served as the study’s lead corresponding author.
“This tool can be used to image various nanoscale objects, such as molecular chains, viruses, lipids, and composite particles. Pharmaceutical companies might utilize this technique to study how viruses interact with cells under varying conditions, which can influence drug development.”
Interestingly, an electron microscope is not essential for activating particles in practical morphable materials; changes in light and pH could achieve that as well.
However, to broaden this method for different types of nanoparticles, the researchers must understand how to adjust liquid compositions and microscope settings to manipulate particle arrangements. The computer simulations executed by the U-M team assist in this future work by explaining the forces that lead to particle interactions and assembly.
“We believe we now comprehend enough of the underlying physics to forecast what might occur if we employ particles of alternative shapes or materials,” stated Tim Moore, an assistant research scientist of chemical engineering at U-M and co-first author of the study. He co-designed the computer simulations with Dwyer and Sharon Glotzer, the Anthony C. Lembke Department Chair of Chemical Engineering at U-M and a corresponding author of the study.
“The fusion of experiments and simulations is thrilling since it gives us a framework to design, predict, fabricate, and observe in real time new morphable materials alongside our collaborators at IU,” remarked Glotzer, who also holds the John Werner Cahn Distinguished University Professorship and the Stuart W. Churchill Collegiate Professorship in Chemical Engineering.
This research was supported by the National Science Foundation.
