Mines Researcher Creates Nanoparticle Pinwheels

Shan Zhou, Ph.D., an assistant professor in the Department of Nanoscience and Biomedical Engineering at South Dakota Mines, made a breakthrough in the creation of nanoscale structures that could change medicine, computing, clean energy and more.

The nanoparticle sheets that Zhou creates are self-assembled nanoscale pyramids with a unique property, chirality; this means the sheets and their mirror images cannot be superimposed. Chiral structures are everywhere in nature, for example, the way the palms of your hands mirror each other as opposites. This same chirality is repeated across many scales, from the structure of DNA to the layout of galaxies. But, until now, it's been difficult to replicate chirality in the microscopic structure of a synthetic material.

Zhou is the lead author on research recently published in the journal Nature with Qian Chen's group at the University of Illinois and Nicolas Kotov's group at the University of Michigan. He says synthesizing chiral nanoparticle sheets, or lattices, has been a holy grail for researchers because of the huge range of applications they may provide. This work could lead to new types of machine vision, enable manufacturing of new medicines and chemicals or it might help create self-healing materials like those envisioned in science fiction movies, such as “Terminator II."

Zhou and others on the research team used nano-sized gold pyramids with a triangle base, known as tetrahedrons, arranged in lattices where the tetrahedrons are packed together in low density. He found that, with the right chemical combination, the tetrahedrons would twist inside the sheets to form pinwheel shapes. This short video in the Nature article shows the transformation. Because of their unique shape, the sheets cannot be superimposed on their mirror images. The research also found that the amount of twisting of individual tetrahedrons could be varied depending on the chemicals added to the lattice. This means the materials can be tuned to exhibit different properties.

“What's interesting is this pinwheel structure was never before predicted in models or theory,” says Zhou, “Once we did further testing, we were very surprised to find it showed these unique chiral properties.” Zhou credits a Multidisciplinary University Research Initiative grant through the Office of Naval Research for support along with collaborating scientists at Argonne National Laboratory and the University of Michigan for assisting in the testing of this material.

Zhou came to Mines in 2022 after completing his postdoctoral research at the University of Illinois, and he is continuing to seek new discoveries in this area of research. “The next thing that we are trying to do with nanoparticle self-assembly is to obtain materials with properties similar to those portrayed in the ‘Terminator II' movie, where self-healing materials come back together after they are deformed,” says Zhou. “Because of the unique properties of this synthetic material, the geometric features that make up the pinwheel lattice do not need energy input to reconfigure themselves after a disturbance.”

Zhou founded the Materials-Interfaces Imaging and Design Laboratory at South Dakota Mines to further explore the unique properties of these new materials. His lab aims to create detailed high-resolution 3D imaging capabilities for nanoparticles and molecules, study nano scale interactions and responses at the surfaces of synthetic and biologic materials and offer future engineering strategies for developing new natural and artificial materials systems. The work could help solve challenges in clean energy and biomedicine. Zhou's lab offers unique expertise in nanoparticle synthesis, self-assembly, electron microscopy and atomic force microscopy. “We are actively looking for undergraduate and graduate students and welcome future collaborations,” he says.

Read more about this work in this press release from the University of Illinois.