New technique lets scientists view nanoparticles as individuals

Scientists at Chalmers University of Technology have developed a new way to study nanoparticles one at a time, which has revealed that individual particles that may seem identical in fact can have very different properties. The results are published in Nature Materials.

“We were able to show that you gain deeper insights into the physics of how nanomaterials interact with molecules in their environment by looking at the individual nanoparticle as opposed to looking at many of them at the same time, which is what is usually done,” says associate professor Christoph Langhammer, who led the project.

By applying a new analytical technique called plasmonic nanospectroscopy, the group studied hydrogen absorption by single palladium nanoparticles. This technique takes advantage of the fact that hydrogen molecules absorbing and desorbing on a palladium nanoparticle alter the scattering of visible light by nearby gold nanoparticles. The group found that particles with exactly the same shape and size absorb hydrogen at pressures that can differ by up to 40 millibars. This finding could help in the development of sensors that detect hydrogen leaks in fuel cell-powered cars.

“One main challenge when working on hydrogen sensors is to design materials whose response to hydrogen is as linear and reversible as possible,” explains Langhammer. “In that way, the gained fundamental understanding of the reasons underlying the differences between seemingly identical individual particles and how this makes the response irreversible in a certain hydrogen concentration range can be helpful.”

Other research groups have studied nanoparticles one at a time, but the advantage of this new approach is its use of visible light with low intensity to study the particles. This means that the method is non-invasive and does not disturb the system it is investigating by, for example, heating it up.

“When studying individual nanoparticles you have to send some kind of probe to ask the particle ‘what are you doing?’. This usually means focusing a beam of high-energy electrons or photons or a mechanical probe onto a very tiny volume,” says Langhammer. “You then quickly get very high energy densities, which might perturb the process you want to look at. This effect is minimized in our new approach, which is also compatible with ambient conditions, meaning that we can study nanoparticles one at a time in as close to a realistic environment as possible.”

Langhammer believes he and his colleagues have so far just scratched the surface of what their new analytical technique could achieve. He hopes they have helped to establish a new experimental paradigm, where looking at nanoparticles individually will become standard in the scientific world.

“It is not good enough to look at, and thus obtain an average of, hundreds or millions of particles if you want to understand the details of how nanoparticles behave in different environments and applications,” he says. “You have to look at individual ones, and we have found a new way to do that.”

“My own long-term vision is to apply our method to more complex processes and materials, and to push the limits in terms of how small nanoparticles can be for us to be able to measure them. Hopefully, along the way, we will gain even deeper insights into the fascinating world of nanomaterials.”

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