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World’s smallest electric motor

  Wednesday 7th September 2011
So small you can’t see it, but it might one day save your life: the nanomotor. Photo: Nature Neuroscience
So small you can’t see it, but it might one day save your life: the nanomotor. Photo: Nature Neuroscience

Chemists have developed the first single-molecule electric motor, so small that it can’t be seen with light – the smallest electric motor engineers have ever created – and it brings hope of future applications both in medicine and nanotechnology.

The motor, reported in Nature Nanotechnology, is composed of two chains of carbon and hydrogen atoms that spin around an atom of sulphur, and is just one nanometer, or 0.000001 of a millimetre, wide.  It is so small that conventional microscopes that use light aren’t powerful enough to see it.

The developers used a low temperature scanning tunnelling microscope (LT-STM), which uses electrons rather than light to produce images, to control it.  The STM has a tip just one or two atoms wide, which directs electrons into the motor in order to both provide it with electrical charge and to take images of it.

The miniscule motor could be useful in medicine in the future. It could, for example, deliver drugs to targeted locations in the body.

While tiny motors have previously been developed that are powered by light or chemical reactions, this is the first one to be electrically driven, allowing much more control of its rotation.

Charge from the microscope (grey, top) directs electric charge to the sulphur atom (yellow), causing the chains of carbon (grey) and hydrogen (white) atoms to rotate around it.

Charge from the microscope (grey, top) directs electric charge to the sulphur atom (yellow), causing the chains of carbon (grey) and hydrogen (white) atoms to rotate around it.

The motor had to be cooled to 5 kelvin (-268°C) to slow the atoms down sufficiently for the engineers to track its rotation.  At the moment this is something of an obstacle to potential applications, but if breakthroughs are made it could be deployed to administer drugs to targeted parts of the body.  Prof. E. Charles H. Sykes, a member of the team who developed it, commented: “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. Coupling molecular motion with electrical signals could also create miniature gears in nanoscale electrical circuits; these gears could be used in miniature delay lines, which are used in devices like cell phones,” he told Science Daily.

The team are currently in talks with the Guinness Book of World Records to get it recorded as the smallest motor in the world.

Emma Roscow

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