The world's smallest electric motor

Researchers at Tufts University in Massachusetts have created the world's smallest electric motor, the size of a single molecule, recently publishing the results in the scientific journal Nature Nanotechnology. Although applications for the nanoscale device are a long way off, the achievement could one day lead to nanoscale machines capable of performing surgery on a single cell, for instance.

The motor is made of a single molecule of butyl methyl sulfide—basically a sulfur molecule with two "arms" made of carbon and hydrogen atoms (the yellow-and-green dots in the middle of the photo to the left). When laid on a copper (the orange dots) and stimulated with electricity, the molecule began to rotate, swinging its arms round and round, just a like a macroscopic motor. The whole device is just one nanometer across (a human hair is about 60,000 nanometers thick). Motors this small have been demonstrated before, but they've been powered by heat, chemicals, or light. This is the first molecular motor to run on electricity.

Like the scientists who first mapped electron orbitals, the team used a Scanning Tunneling Microscope to get their molecule motor running. The microscope is the only tool capable of probing such small distances, and without precise manipluation of individual molecules, the runnings of one molecular motor would end up interfering with another. Imagine two wind turbines whose blades are so close they would hit each other if both were turned on.

A big caveat of the discovery is that the motor is only measurable at extremely cold temperatures. To perform their experiment, the Tufts researchers cooled the sample down to about minus 450 degrees Fahrenheit, slowing the molecules down to the point where the number of rotations per second was about 50. The motor still rotated at higher temperatures, but the number of rotations was off the scale. At minus 279 degrees Fahrenheit, for example, the number of rotations was more than a million every second.

"It's not that we couldn't work at a higher temperature - it's just that too much is happening," lead scientist Charles Sykes told Tufts Now. "At that speed, it's just a blur."

So what good is a molecule-size motor? Assuming the temperature issue can be addressed (which could take decades, if ever), the discovery may end up powering nanotechnology-based devices. In medicine, a device that small could be introduced to a person's body to perform procedures on individual cells. In engineering, tony motors could power nanoscale machines like sensors.

At the very least Sykes' team has guaranteed their creation a spot in the Guinness Book of World Records... at least until someone creates an atomic-scale motor.

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