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Watch nanotubes wriggle to form a bridge

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Researchers inspired by a high-wire act and fly fishing have coaxed strings of synthetic DNA to build microscopic bridges between molecules on the surface of a lab dish.

They describe this process, which could someday be used to connect electronic medical devices to living cells, in the journal Nature Nanotechnology.

nanotube gif

Senior author Rebecca Schulman, assistant professor of chemical and biomolecular engineering at Johns Hopkins University, compares the process to the death-defying stunt in the movie Man on Wire. The film depicts Philippe Petit’s 1974 high-wire walk between the New York World Trade Center’s twin towers.

That real-life crossing could not have been accomplished without a critical piece of old-fashioned engineering, Schulman says: Petit’s partner used a bow and arrow to launch the wire across the chasm between the towers, allowing it to be secured to each structure.

“A feat like that was hard to do on a human scale,” Schulman says. “Could we ask molecules to do the same thing? Could we get molecules to build a ‘bridge’ between other molecules or landmarks on existing structures?”

nanotube bridge graphic
(Credit: via Johns Hopkins)

Schulman’s collaborator used another analogy to describe bridge building at a scale where distances are measured in millionths or billionths of a meter.

“If this process were to happen at the human scale,” says lead author Abdul Mohammed, a postdoctoral fellow in Schulman’s lab, “it would be like one person casting a fishing line from one side of a football field and trying to hook a person standing on the other side.”

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The researchers used microscopic building blocks formed by short sequences of synthetic DNA, which assemble themselves into long tube-like structures known as DNA nanotubes.

These building blocks attached themselves to separate molecular anchor posts, representing where the connecting bridge would begin and end. The segments formed two nanotube chains, each extending away from its anchor post. Then, like spaghetti in a pot of boiling water, the lengthening nanotube chains wriggled about, exploring their surroundings in a random fashion. Eventually, the separate nanotube strands made contact and snapped together to form a single connecting bridge span.

The researchers used microscopes to record the process. It took about six hours to complete the nanoscale bridge in the video seen above, though the video is accelerated so the process can be seen in seconds. Depending on how far apart the molecular anchor posts were located, the connection process in other trials took anywhere from several hours to two days.

Watch nanotubes self-assemble into tiny wires

The ability to assemble these bridges, the researchers say, suggests a way to build medical devices that use wires, channels, or other devices that could “plug in” to molecules on a cell’s surface. Such technologies could be used to understand nerve cell communication or to deliver therapeutics with unprecedented precision.

Molecular bridge-building, the researchers says, is also a step toward building networked devices and “cities” at the nanoscale, enabling new components of a machine or factory to communicate with one another.

John Zenk, who recently received his PhD from Johns Hopkins, and Petr Šulc, a postdoctoral fellow at Rockefeller University, are coauthors of the study. Funding came from the Department of Energy, the National Science Foundation, and the Simons Foundation.

Source: Johns Hopkins University

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