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Wet nanoribbons loop like DNA and fold like proteins

Graphene nanoribbons are known for adding strength but not weight to composites, like bicycle frames and tennis rackets. Now researchers say they could be useful in a squishier environment.

It turns out the tiny ribbons bend and twist easily in solution, making them adaptable for biological uses like DNA analysis and drug delivery. They also might be useful for biomimetic materials—those that imitate the forms and properties of natural materials.

“We like to see how materials behave in solution, because that’s where biological things are.”

Their incredibly small size means they can operate on the scale of biological components, says Rice University physicist Ching-Hwa Kiang, whose lab employed its unique capabilities to probe nanoscale materials like cells and proteins in wet environments.

“We study the mechanical properties of all different kinds of materials, from proteins to cells, but a little different from the way other people do,” she says. “We like to see how materials behave in solution, because that’s where biological things are.”

The ability to conform to surfaces, carry current, and strengthen composites could be valuable when applied to a solution.

“It turns out that graphene behaves reasonably well, somewhat similar to other biological materials. But the interesting part is that it behaves differently in a solution than it does in air,” she says.

The research led by recent Rice graduate Sithara Wijeratne, now a postdoctoral researcher at Harvard University, appears in the journal Scientific Reports.

The researchers found that like DNA and proteins, graphene nanoribbons (GNRs) in solution naturally form folds and loops, but can also form helicoids, wrinkles, and spirals.

Kiang and colleagues used atomic force microscopy to test their properties. Atomic force microscopy can not only gather high-resolution images but also take sensitive force measurements of nanomaterials by pulling on them. The researchers probed GNRs and their precursors, graphene oxide nanoribbons.

nanoribbon experiment illustration
The tip of an atomic force microscope on a cantilevered arm is used to pull a graphene nanoribbon the same way it would be used to pull apart a protein or a strand of DNA. The microscope can be used to measure properties like rigidity in a material as it’s manipulated by the tip. (Credit: Kiang Research Group/Rice University)

The researchers discovered that all nanoribbons become rigid under stress, but their rigidity increases as oxide molecules are removed to turn graphene oxide nanoribbons into GNRs. They suggested this ability to tune their rigidity should help with the design and fabrication of GNR-biomimetic interfaces.

“Graphene and graphene oxide materials can be functionalized (or modified) to integrate with various biological systems, such as DNA, protein, and even cells,” Kiang says. “These have been realized in biological devices, biomolecule detection, and molecular medicine. The sensitivity of graphene bio-devices can be improved by using narrow graphene materials like nanoribbons.”

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Wijeratne notes that graphene nanoribbons are already being tested for use in DNA sequencing, in which strands of DNA are pulled through a nanopore in an electrified material. The base components of DNA affect the electric field, which can be read to identify the bases.

The researchers saw nanoribbons’ biocompatibility as potentially useful for sensors that could travel through the body and report on what they find.

Further studies will focus on the effect of the nanoribbons’ width, which range from 10 to 100 nanometers, on their properties.

The Welch Foundation and the National Science Foundation supported the research.

Source: Rice University

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