A team led by Northwestern University and the University of Michigan has created a novel way of assembling particles into colloidal crystals, a valuable form of material utilized in chemical and biological sensing as well as light-detecting devices. For the first time, the team has demonstrated that these crystals can be built in ways that are not present in nature using this technology.
To confirm their important discovery, the researchers employed the Advanced Photon Source (APS), a US Department of Energy (DOE) Office of Science user facility at the DOE’s Argonne National Laboratory.
The high-resolution measurements required to analyze this type of assemblage are made possible by a strong X-ray beam. “The APS is an excellent location for this study,” Argonne National Laboratory’s Byeongdu Lee commented.
“A powerful X-ray beam enables the high-resolution measurements you need to study this type of assembly. The APS is an ideal facility to conduct this research,”
Byeongdu Lee of the Argonne National Laboratory.
Chad A. Mirkin, the George B. Rathmann Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences, said, “We’ve discovered something fundamental about the system for making new materials.” “Breaking symmetry in this way rewrites material design and synthesis laws.”
The research, which was published in Nature Materials, was led by Mirkin and Sharon C. Glotzer, the Anthony C. Lembke department chair of Chemical Engineering at the University of Michigan.
Colloidal crystals are very small particles with smaller particles (called nanoparticles) arranged in an ordered or symmetrical pattern inside of them. They can be designed for a variety of purposes, including light sensors and lasers, as well as communications and computation. For this study, scientists attempted to violate nature’s innate symmetry, which tends to organise microscopic particles in the most symmetrical way possible.
“Imagine stacking basketballs in a box,” said Argonne’s Byeongdu Lee, an author on the paper and a group leader at the APS. You’d have a precise method for accomplishing it that maximizes the space’s worth. That’s the way nature works. “
However, Lee claims that if the balls are deflated enough, they can be stacked in a different arrangement. According to him, the research team is attempting to educate nanomaterials to self-assemble into new designs in the same way.
In this study, DNA, the molecule inside cells that carries genetic information, was employed. Scientists have gleaned enough information about DNA to be able to program it to perform specific tasks. This study used DNA to instruct metal nanoparticles on how to form novel structures. Researchers bonded DNA molecules to the surfaces of nanoparticles of various sizes and discovered that the smaller particles migrated around the larger particles in the gaps between them, forming a new substance.
“Building intricate colloidal crystal structures with large and small nanoparticles, where the smaller ones move around like electrons in a crystal of metal atoms,” Glotzer added.
Scientists adjusted the characteristics of the little electron-equivalent particles by altering this DNA, and therefore modified the crystals that resulted.
“We looked at more sophisticated architectures where the number of neighbors around each particle may be controlled to induce additional symmetry breaking,” Glotzer added. “Our computer simulations assisted in deciphering the complex patterns and revealing the mechanics by which the nanoparticles were able to form them.”
This method paved the way for the creation of three novel, never-before-synthesized crystalline phases, one of which has no natural counterpart.
“In the natural atomic system, colloidal particle assemblages always have some analogy,” Lee remarked. This time, we discovered a whole different structure. We’ve never seen metals, metal alloys, or other things naturally organize themselves in this way before. “
“We don’t know the material’s physical properties yet,” Lee explained. “Now it’s up to the materials scientists to build and research this substance.”
The scientists used the APS’s ultrabright X-ray beams to check the new structure of their crystals. They used high-resolution small-angle X-ray scattering devices on beamlines 5-ID and 12-ID to create exact images of the particle arrangements they had created.
“A powerful X-ray beam permits the high-resolution measurements required to analyze this type of construction,” Lee explained. “The APS is a great facility for this study.”
According to Lee, the APS is currently undergoing a huge update that will enable scientists to determine even more complex structures in the future. The instruments at 12-ID are also being modified so that they can fully utilize the stronger X-ray beams that will be available.
These low-symmetry colloidal crystals have optical features that conventional crystal forms cannot match and may find applications in a variety of technologies. Their catalytic characteristics are also distinct. However, the new structures revealed here are simply the tip of the iceberg in terms of the possibilities now that the requirements for breaking symmetry are known.
“We are living in an unprecedented period of materials synthesis and discovery,” Mirkin added. “This is another step toward getting novel, undiscovered materials out of the lab and into applications that can benefit from their unique and unusual features.”
