Liquid drop takes big nano step

By Jonathan Amos
BBC News science reporter, Dublin

PROPELLED BY NANOMACHINES (1) The drop sits on a surface coated with an extremely thin layer of nanomachines Each nanomachine is little more than a nanometre in size (a millionth of a millimetre) These molecules essentially look like rods with rings that furiously slide back and forth (2) When the light is switched on, a chemical reaction pushes all the rings down to one end The surface then changes; it ceases to be repulsive and becomes attractive This alters the nature of the surface tension in the drop and it begins to move

Edinburgh scientists have made a small blob of liquid move across a surface by shining a light in front of it.

It may not sound like much but the molecular engineering that went into this feat is said to be a step forward in the emerging area of nanotechnology.

The trick is in tiny "machines" about a millionth of a millimetre in size that coat the surface and propel the drop.

The team envisages this technology moving biological samples around a diagnostic chip to detect disease.

The researchers can also see their work leading to smart materials that change their shape at the flick of a switch.

Professor David Leigh, of the University of Edinburgh, said the demonstration was one of the first examples to show molecular machines integrating successfully with the macroscopic world.

"The components of these machines only move a nanometre but they are able to move the droplet by a whole millimetre.

"That's six orders of magnitude greater - equivalent to a piston moving a millimetre in the macroscopic world and being able to lift an object twice the height of the CN Tower."

New world

The tiny machines that coat the surface are essentially rod-like structures with rings that, in their normal state, furiously jump up and down because of Brownian motion (the random movement of molecules caused by collisions with molecules around them).

But when these structures are stimulated by ultra-violet light, a chemical reaction takes place and the rings all go to one end, changing the nature of the surface under the blob from a repulsive one to an attractive one.

This dramatically alters the surface tension of the liquid droplet above and it begins to move - even up a slight incline.

Professor Leigh concedes the work is early proof-of-principle but he is bolstered by the knowledge that nature uses molecular machines to do all of its jobs. He believes it can only be a matter of time before we are tapping into that know-how.

"Mankind, despite all of our technology in the 21st century, we use molecular machines to do nothing," he told the British Association's Festival of Science here in Dublin, Ireland.

"The properties of every drug, every polymer and every catalyst are just based on their static or non-smart properties. When we learn to do the same as nature, you really will have materials that today just sound like science fiction."

Professor Leigh's group at Edinburgh published their work this week in the journal Nature Materials.