Thursday, 17 April 2014
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Graphene improves resolution of atomic-level images

By sandwiching a biological molecule between sheets of graphene, researchers at the University of Illinois at Chicago have obtained atomic-level images of the molecule in its natural environment.

The results are published in the journal Advanced Materials.

The molecule, ferritin, is a protein that regulates the levels of iron in animals and plants. Ferritin can sequester excess iron, which can be toxic, and release it when it is needed.

‘We found a way to encapsulate a liquid sample in two very thin layers of graphene - sheets of carbon that are only one atom thick,’ said Canhui Wang, UIC graduate student in physics and first author of the study.

Electron microscopes let researchers see at the level of individual atoms but to do so they must put the samples in a vacuum, making it impossible to image biomolecules in water in their natural, functional state. Biological samples have usually been placed in a container called a ‘liquid stage,’ wedged between relatively thick windows of silicon nitrate.

Robert Klie, the senior investigator on the study, said the thin layers of graphene in the new system work better, being nearly transparent.

‘It’s like the difference between looking through Saran Wrap and thick crystal,’ said Klie, who is associate professor of physics and mechanical and industrial engineering at UIC.

As well improving resolution the graphene sandwich also minimises damage to the sample from radiation, Wang said in a statement.

According to Wang, some people have calculated that to barely visualise a sample requires the equivalent of 10 times the radiation 30 meters away from a 10 megaton hydrogen bomb. ‘We often use an electron beam that is several orders of magnitude more intense in our experiments,’ he said.

Graphene has an extraordinarily high thermal and electro-conductivity, said Klee, and is able to conduct away both the heat and the electrons generated as the electron microscope’s beam passes through the sample.

Instead of using a low-energy beam to minimise damage, which yields a fuzzy picture that must be refined using a mathematical algorithm, the scientists were able to use high energies to generate images of ferritin at atomic level resolution. This enabled them to see, in a single functioning molecule, that iron oxide in ferritin’s core changes its electrical charge, initiating the release of iron.

This insight into how the ferritin core handles iron may lead to a better understanding of what goes wrong in many human disorders, said Tolou Shokuhfar, assistant professor of mechanical engineering-engineering mechanics at Michigan Technological University and adjunct professor of physics at UIC, the principal investigator of the study.

‘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 Shokuhfar.

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