US researchers claim to have developed the world`s first single-molecule electric motor. The scientists, from Tufts University`s School of Arts and Sciences, say that their motor is just 1nm wide – 60,000 times thinner than a human hair – and suggest that it could create a new class of device with applications ranging from medicine to engineering.

The new motor is 200 times smaller than the previous smallest molecular machine. “There has been significant progress in the construction of molecular motors powered by light and by chemical reactions,” explains Dr Charles Sykes, associate professor of chemistry at Tufts, “but this is the first time that electrically-driven molecular motors have been demonstrated, despite a few theoretical proposals. We have been able to show that you can provide electricity to a single molecule and get it to do something that is not just random.”

Sykes and his colleagues control their motor using a low-temperature scanning tunnelling microscope (LT-STM), which uses electrons to “see” molecules. The microscope’s tiny metal tip provides an electrical charge to a butyl methyl sulphide molecule placed on a conductive copper surface (above). This molecule has carbon and hydrogen atoms radiating from it to form what look like two arms, with four carbons on one side and one on the other. These carbon chains were free to rotate around the sulphur-copper bond at speeds of up to 120 rpm.

By reducing the temperature of the molecule to around 5K (–268°C), the team found they could affect its rotation. At higher temperatures, the motor spins much faster, making it difficult to measure and control the rotation. To achieve practical applications, breakthroughs will need to be made in the operating temperatures.

“Once we have a better grasp on the temperatures necessary to make these motors function, there could be real-world application in some sensing and medical devices which involve tiny pipes,” Sykes suggests. “Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along. Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits. These gears could be used in miniature delay lines, used in devices like cell phones.”

The Tufts researchers have published a paper on their molecular motor in Nature Nanotechnology and plan to submit it for a Guinness world record.