Scientists in New York have created a nanometre-sized moving arm from synthetic DNA. This kind of mechanical device, which operates on an molecular scale, is seen as the precursor for nano-robots which will manufacture or repair molecules, possibly within the human body.

The future uses of mechanical DNA devices are revealed by Professor Nadrian Seeman

"All of the DNA-based self-assembly molecules we have created before now are static," Professor Nadrian Seeman of New York University told BBC News Online. "Now it's time to have control over the motion, not just the shape."

"The ultimate uses of this new moecule will be in the analytical, in the laboratory, and also techological. Ultimately we will be able to make small nanomachines that can do molecular manufacturing and then step up to nanorobots."

10 year timescale

The DNA link switches from spiralling in a right-handed direction to a left-handed direction

How long these will take to develop depends on how you define a robot, says Professor Seemen. "If it's a fully-controllable electrical device you are probably talking about 10-20 years down the line, if you mean a robot that's roaming around and looking anthropoid then a bit further."

The new device, reported in Nature, has two rigid DNA arms linked by a special piece of DNA. This helix in this special piece winds in the usual direction, right-handed.

However, when a cobalt compound is put into solution and comes close to the linking DNA, the interaction of electrical charges causes the linking piece to flip into a helix wound in the opposite direction.

This flip means that the two arms connected move away from each other by up to 6 nanometres, a significant distance in the nano-world.

Nano-scale arm

The nanotechnologist Professor Seeman explains how the DNA robotic arm works

"It is actually rather large scale," explains Professor Seemen. "There are a few small chemicals already with small scales of motion, but this is first device with such a large range. In the future we will think about combining our DNA device with the smaller chemical ones - our device giving motion comparable to forearm over elbow, the smaller ones' motion more like wiggling a finger."

With such a tiny machine, the researchers had to devise a way of seeing whether it had actually moved after the cobalt hexamine is added. At each end of the two DNA arms they placed fluorescent dye molecules.