A nanotechnologist has created the world's smallest and most plentiful Smiley -- a tiny face measuring a few billionths of a meter across that is assembled from strands of DNA.
Some fifty billion Smileys, each a thousand times smaller than the diameter of a human hair, can be made at a stroke using the technique pioneered by Paul Rothemund at the California Institute of Technology (Caltech).
DNA, the molecule that comprises living things, has long been known for its versatility as a microscopic building block.
The molecule can be "cut" using enzymes and reassembled using matching rungs in its double-helix structure. This theoretically opens the way to making DNA quantum computers and nano-level devices including injectable robots that can monitor the body's tissues for good health.
But, until now, nano-assembly has been a complex atom-by-atom procedure that is also costly, because it is carried out in a vacuum or at extremely cold temperatures.
Rothemund, writing in yesterday's issue of Nature, describes a far simpler and much cheaper process in which long, single strands of DNA can be folded back and forth to form a basic scaffold.
The basic structure is then supplemented by around 200 shorter strands, which both strengthen it and act rather like pixels in a computer or TV image, thus providing a shape that can bear a complex pattern.
In a potent demonstration of his so-called DNA origami technique, Rothemund has created half a dozen shapes, including a five-pointed star, a snowflake, a picture of the double helix and a map of the Americas in which one nanometre (one billionth of a meter) represents 120km.
Rothemund has been working on flat, two-dimensional shapes but says that 3-D structures in DNA should be quite feasible with this technique, Caltech said in a press release.
One application would be a nano-scale "cage" in which pharmaceutical researchers, working on novel drugs, could sequester enzymes until they were ready for use in turning other proteins on and off.
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