Smallest motor

Researchers at Tufts University have made the world's smallest electric motor from a single molecule that measures a mere 1 nanometer across.

The team, led by Professor Charles H. Sykes, plans to submit the breathtaking achievement to Guinness World Records. The new class of device could be used in applications ranging from medicine to engineering.

The single molecule electric motor measures 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.

The research team published a paper detailing the new electric motor in Nature Nanotechnology on Sunday.

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.

Single-molecule motors are not new, and previous research groups had shown an ability to get individual molecules to respond to stimulus from light or from chemicals. But this is the first time that electrically-driven molecular motors have been demonstrated despite a few theoretical proposals and it has significant advantages over those other technologies.

 The team used a scanning tunneling 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.

The team then determined that by controlling the temperature of the molecule they could directly impact its rotation. They found that approximately 5 Kelvin (K), or about minus 450 degrees Fahrenheit (ºF), proved ideal for tracking the motor's motion as direction and speed were affected by temperature.

At higher temperatures, the motor spins much faster, making it difficult to measure and control the rotation. To achieve practical applications, breakthroughs need to be made in the operating temperatures.

That's because as temperatures rise, the motor spins much faster, far beyond the ability of the scientists to measure the rotations. At 100K, a molecular motor spins more than a million times per second, said Sykes.

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, added Sykes.

Sykes said 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.

Friction of the fluid against the pipe walls increases at these small scales, and covering the wall with motors could help drive fluids along.

By slightly modifying the molecule, the molecular electric motors could be used to generate microwave radiation or to couple into nano-electromechanical systems (NEMS).

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, BBC quoted Sykes as saying.

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