A Tufts University (US) research team has developed the world’s first single-molecule electric motor—which is a mere 1 nanometer across. They reported the results in a paper published recently in Nature Nanotechnology. This development—made possible with a low-temperature scanning tunneling microscope at Tufts, one of only about 100 in the US—may be the first step toward a new class of devices that could be used in applications ranging from medicine to engineering.

“The excitement is in the demonstration that you can provide electricity to a single molecule and get it to do something that’s not just random,” says team leader Charles Sykes, an associate professor of chemistry in the School of Arts and Sciences.

Single-molecule motors are not new, but until now they’ve been driven by either chemicals or light. A molecular motor powered by electricity has significant advantages over those other technologies, says Sykes. He explains that to power molecular motors with chemicals, scientists must add chemicals to a beaker filled with trillions of molecules. “So there are limited things you can do to that,” he points out. Likewise, using light to power molecular motors creates difficulties, because even very tightly focused light will hit many molecules at once.

With the scanning tunneling microscope, “we can land just on top of one molecule, measure it and spin it,” Sykes says. “It’s the ultimate way to do it.”

Sykes and his colleagues used the metal tip of the microscope to provide an electrical charge to a butyl methyl sulphide molecule that had been placed on a copper surface. The molecule had a sulphur atom at the centre and carbon atoms radiating off to form two arms, so to speak: four carbons on one side, one on the other. In subsequent experiments, such arms could potentially act as interlocking cogs or gears, and as one molecule is powered, it could turn or rotate others in sequence.