Tiny robots powered by ANTs

Nanobots have long been dreamed of by scientists for applications such as drug delivery.

But making a moving robot on the nano scale - a hundred thousand times smaller than the width of a human hair - is difficult because the forces needed for movement are enormous compared to the size of the object.

'When we try to make things move in water and they're very small, it's a bit like us trying to swim in treacle,' Professor Jeremy Baumberg told the Naked Scientists.

'It's very difficult to do as it needs a lot of force and we haven't been able to make things that produce such a large force on a really small scale before.'

But now, Baumberg and his team from the University of Cambridge have managed to make a nano-device which produces the large force needed for movement simply by shining light on it. 

Publishing in PNAS last week the researchers have called the devices ANTs (actuating nanotransducers) because, like the little insects, they produce large forces for their size.

The ANTs are made up of nano-sized pieces of gold, which are coated with a gel.

Below 30 degrees this combination is hydrophilic - it prefers to be in contact with water - and so it spreads out.

But when the temperature is increased above 30 degrees, the interaction with water changes and it becomes hydrophobic - water hating - so that the ANTs scrunch up, much like a loaded spring.

Cooling the mixture back down again releases this large store of energy, similar to an explosion, and it's this force which is the first step in making nano-devices move.

Changing between the water loving and water hating phases can be done by heating, but it can also be done with light, chemicals or even magnets.

The components are also all easily available and they can even swap out the gold to use cheaper metals so scale up of these devices should be straight forward.

Despite the early stage of the research Baumberg already has ideas for application in an area called microfluidics.

This is a growing area which could be used for quickly testing lots of drugs and involves doing a chemical reaction on a tiny chip by automation.

By shining light on the device, the ANTs could be used to pump liquid around, which is currently a challenge on such a small scale.

The ANTs could also have great potential for use in the body, because they work in water and they are biocompatible which means the body won't reject them, although widespread medical application is a few years off.

'For applications where we use them in the body we really don't know how to do that yet. One of the good things is we don't just have to use light to make these things open and close so it's actually a rather generic technology. And yes we have to find out what's the killer application. Or maybe the non-killer application for the body!' joked Baumberg.