Single Molecule Electric Motor: a New Hope in Nanoscience

The world's smallest motor made from a single molecule is going to set a new record in the Guinness World Records and gives much hope to scientists for its practical application in Nanoscience.

A team of researchers from Tufts University used a single molecule to create the smallest electric motor ever, measuring one nanometer across, which is one billionth of a meter.

This means, the microscopic motor is 60,000 times smaller than a single strand of a human hair, excelling far beyond the current world record held by a 200 nanometer motor.

There has been significant progress in the construction of molecular motors powered by light and by chemical reactions, but this is the first time that electrically-driven molecular motors have been demonstrated, despite a few theoretical proposals, said E. Charles H. Sykes, Ph.D., associate professor of chemistry at Tufts who led the team.

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.

The team used a scanning tunnelling microscope that shows molecules through electrons instead of light, and managed to spin a single butyl methyl sulfide molecule. They used the metal tip of the microscope to provide an electrical charge to the molecule that had been placed on a copper surface.

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.

Scientists found that a freezing minus 450 degrees Fahrenheit proved ideal for tracking the motor's motion as direction and speed were affected by temperature.

At higher temperatures, the motor spins too fast to observe and control.

It's not that we couldn't work at a higher temperature - it's just that too much is happening. At that speed, it's just a blur, said Sykes.

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, said Sykes.

The single molecule electric motor could lead to new types of electrical circuitry, giving hope for scientists to apply it in medicine and engineering.

To power individual molecules, electricity gives higher precision than light and chemicals, because you're driving billions of them at a time, explained Sykes to the BBC. With electricity, we can land just on top of one molecule, measure it and spin it, said Sykes, adding that it is the ultimate way to drive molecules precisely. The new method gives great hope for scientists in advancing nano-sensors and in medicine.

One of the goals of Nanoscience is to use individual molecules to make all types of common devices, said Sykes.

Molecular electric motors can be used in nano-electromechanical systems. For instance, coupling molecular motion with electrical signals may allow scientists to build signal delay lines and nano-scale sensors.

Another use could be in sensing and medical test devices that involve tiny pipes. At these small scales, friction of the fluid against the pipe walls increases, and covering the walls with motors may help drive the fluids along, Sykes said.

The next thing to do is to get the thing to do work that we can measure - to couple it to other molecules, lining them up next to one another so they're like miniature cog-wheels, and then watch the rotation propagation down the chain, said Sykes.