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Last Updated: Wednesday, 15 March 2006, 23:41 GMT
Nanotech discovers the Americas
A powerful atomic force microscope is needed to see the shapes (Image: P Rothemund)

It is without question the smallest map that has ever been made.

US scientists have coaxed strands of DNA, the molecule that holds the "code of life", to take up a shape that resembles the Americas.

The mini-map measures just a few hundred nanometres (billionths of a metre) across, smaller even than some bacteria - a scale of 1:200 trillion.

Paul Rothemund, from the California Institute of Technology, and colleagues report their cartography in Nature.

They tell the journal their technique could find uses in the emerging field of nanotechnology, which aims to develop novel materials, devices and systems by manipulating individual atoms and molecules.

The team's work exploits the very particular bonding that takes place in DNA.

Graphic, BBC
The double-stranded DNA molecule is held together by four chemical components called bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
Groupings of these "letters" form the "code of life"; there are about 2.9 billion base-pairs in the human genome wound into 24 distinct bundles, or chromosomes
Written in the DNA are about 20-25,000 genes which human cells use as starting templates to make proteins; these sophisticated molecules build and maintain our bodies
Each strand of the molecule will have a sequence of chemical components, or bases, which will only attach themselves to a complementary sequence on another DNA strand (see box).

The researchers made long single strands of DNA that could be folded back and forth, tracing a mazelike path, to form a scaffold that filled up the outline of any desired shape.

To hold the scaffold in place, shorter DNA strands were then bound to the scaffold to "staple" it together.

This produced a pixel-like effect, akin to a computer image. The shapes and patterns are each about 100 nanometres in diameter - or about a thousand times smaller than the diameter of a human hair. The pixels themselves are six nanometres in diameter.

Rothemund's team has created half a dozen shapes, including a square, a triangle, a five-pointed star, and a smiley face.

Scientists have for some time now been able to coax DNA to take up specific shapes and even produce machine-like behaviour; but this latest work is said to have made the whole manipulation process easier and speedier.

Face  (Paul Rothemund)
A smiley and a hexagon (Images: Nick Papadakis & Paul Rothemund).

UK orders another nanotech review
25 Feb 05 |  Science/Nature
Myths and realities of nano futures
28 Jul 04 |  Science/Nature
Tiny robot walker made from DNA
06 May 04 |  Science/Nature
DNA makes tiny tweezers
09 Aug 00 |  Science/Nature

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