BBC News Online / Sci-Tech
January 13, 1999
It's one small step for DNA, one vast leap for
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.
"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 molecule 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
10 Year timescale
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
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
"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.
When the DNA link is untwisted the dyes sit next to each
other and flourescent light is given off. When the link
twists and the arms move the dyes are separated making the
solution go dark.
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