Graphene Sandwich Improves Biomolecule Imaging

Atomic-level images of a biological molecule in its natural environment can now be obtained by sandwiching the wet sample between sheets of graphene.

A team at the University of Illinois at Chicago developed the technique, which shows the molecule ferritin — a highly conserved protein that regulates and sequesters excess, potentially toxic iron levels, and releases iron when needed — in its natural, watery environment. Historically, such a view has been impossible because electron microscopes require that samples be in a vacuum. Biological samples typically have been contained in what is called a “liquid stage,” wedged between relatively thick silicon nitrate windows.

The thin layers of graphene in the new system work better, as they are nearly transparent, said Robert Klie, associate professor of physics and of mechanical and industrial engineering at UIC, and senior investigator on the study.

Atomic-level images of a biological molecule in its natural environment can now be obtained by sandwiching the wet sample between sheets of graphene. Courtesy of the University of Illinois.

"It's like the difference between looking through Saran Wrap and thick crystal," he said.

Graphene has an extraordinarily high thermal and electroconductivity, and is able to conduct away both the heat and the electrons generated as the electron microscope's beam passes through the sample.

Using a low-energy beam to minimize sample damage yields a fuzzy picture that must be refined using a mathematical algorithm. Graphene layers, however, allowed the researchers to generate atomic-level images of ferritin with high energies. In a single functioning molecule, researchers can see that iron oxide in ferritin's core changes its electrical charge, initiating the release of iron.

Identifying how ferritin handles iron may lead to a better understanding of the human disorders caused by iron toxicity.

"Defects in ferritin are associated with many diseases and disorders, but it has not been well understood how a dysfunctional ferritin works towards triggering life-threatening diseases in the brain and other parts of the human body," said Tolou Shokuhfar, principal investigator of the study, and an adjunct professor of physics at UIC and assistant professor of mechanical engineering at Michigan Technological University.

The research was funded by Michigan Technological University and a grant to UIC from the National Science Foundation. It is published in Advanced Materials.

For more information, visit www.uic.edu.