Manufacturing Bits: April 14

Complex microparticles
A team of researchers have developed the world’s most complex microparticle.

In the lab, researchers have assembled hierarchically organized particles with twisted spikes and polydisperse Au-Cys (gold-cysteine) nanoplatelets or nanosheets. The sheets all twist in the same direction. Cysteine is a proteinogenic amino acid.

The structure is said to be more complex than other particles, based on graph theory methods, according to researchers. Applications include new paints as well as new ways to twist light. Complex microparticles could also one day pave the way towards particles that improve biosensors, electronics and chemical reactions.

The research group includes the University of Michigan, the Federal University of São Carlos, the University of São Paulo, California Institute of Technology and the University of Pennsylvania.

Made from curved gold-cysteine nanosheets that all twist in the same direction, the spiky nanoparticle achieved the highest complexity measured. It absorbs UV light and emits twisted light in the visible part of the spectrum. Credit: Wenfeng Jiang, Kotov Lab, University of Michigan

Materials and minerals consist of complex building blocks and particles. Coccolithophore, a unicellular phytoplankton, is one of the most complex particles in nature. “Coccolithophores surround themselves with a microscopic plating made of limestone (calcite),” according to the Earth Observatory at the NASA Goddard Space Flight Center. “These scales, known as coccoliths, are shaped like hubcaps and are only three one-thousandths of a millimeter in diameter.”

Researchers from the University of Michigan and elsewhere devised a gold nanosheet structure that is more complicated than coccolithophores. A key to the technology is the phenomena called chirality, which is the property of a figure that is not identical to its mirror image.

Using the concept of chirality, researchers devised nanoscale gold sulfide sheets with cysteine. “Cysteine comes in two mirror-image forms, one driving the gold sheets to stack with a clockwise twist, and the other tending toward a counterclockwise twist. In the case of the most complex particle, a spiky ball with twisted spines, each gold sheet was coated with the same form of cysteine,” according to the University of Michigan.

Researchers also used electrically charged molecules. This in turn helped ensure that the components were bigger than a few hundred nanometers. “Numbers rule the world, and being able to rigorously describe spiky shapes and put a number on complexity enables us to use new tools like artificial intelligence and machine learning in designing nanoparticles,” said Nicholas Kotov, a professor at the University of Michigan.

Microparticle metrology
The Institute for Basic Science, Monash University and Lawrence Berkeley National Laboratory have developed a microscopy technique that can resolve individual nanoparticles in 3D with atomic-level resolution.

The technology is called 3D SINGLE (Structure Identification of Nanoparticles by Graphene Liquid cell Electron microscopy). Using this technology, individual nanoparticles can be extracted with a precision of 0.02nm, according to researchers. This figure is six times smaller than the smallest atom.

3D SINGLE makes use of a transmission electron microscope (TEM). In a TEM, a nanocrystal solution is sandwiched between two graphene sheets. The TEM fires electron beams at the structure. With the TEM, researchers obtain images of the structure at 400 images per second. Then, researchers combine the 2D images into a 3D map showing the atomic arrangement.

In the lab, researchers defined the atomic structures of eight platinum nanoparticles. “Since graphene is the thinnest and strongest material in the world, we created graphene pockets that allow the electron beam of the microscope to shine through the material while simultaneously sealing the liquid sample,” said Park Jungwon, a co-author of the study and assistant professor at Seoul National University.

“Now it is possible to experimentally determine the precise 3D structures of nanomaterials that had only been theoretically speculated. The methodology we developed will contribute to fields where nanomaterials are used, such as fuel cells, hydrogen vehicles, and petrochemical synthesis,” said Kim Byung Hyo, the first author of the study.

“We have developed a groundbreaking methodology for determining the structures that govern the physical and chemical properties of nanoparticles at the atomic level in their native environment. The methodology will provide important clues in the synthesis of nanomaterials. The algorithm we introduced is related to new drug development through structure analysis of proteins and big data analysis, so we are expecting further application to new convergence research,” added Hyeon Taeghwan, director of the IBS Center for Nanoparticle Research.