Circuit training
The nano-electronics of the future might use DNA to build itself.
28 February 2001
PHILIP BALL
 | | DNA: could help tiny electronic circuits to make themselves |
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Robots that can assemble themselves from components smaller than bacteria are beginning to seem less like science fiction. A team at Pennsylvania State University has used DNA to encourage gold wires millionths of a millimetre across to take up specific positions on a gold surface, bringing self-wiring nano-circuitry within the bounds of possibility.
Thomas Mallouk and co-workers cast the gold wires, 200 nanometres wide and 6,000 nm long, inside the narrow channels of a porous membrane, and tagged most of them with short strands of DNA1.
They then covered a gold film with DNA strands, which matched the strands on some of the nanowires. (Single DNA strands 'match' one another when their sequences are complementary, like the north and south poles of magnets.)
Just like magnets, when complementary strands found each other they made the wires stick to the surface. The wires whose DNA strands matched those on the surface were up to four times more likely to become attached than those with non-complementary DNA tags, Mallouk's group found. Discrimination is not yet perfect, because mis-tagged or even non-tagged nanowires also have a slight tendency to stick.
The researchers now hope to make 'self-wiring' nanoscale electronic circuits, using surface-bound DNA tags to guide the components into place. They also imagine linking the wires to one another by giving them complementary tags at their ends, having already shown a way to tag just the wires' tips. Suitably programmed, the components might then gather spontaneously into a complex circuit.
It's another step forwards from traditional electrical engineering methods of building structures and devices. Instead of, say, carving out every wire and transistor in an integrated circuit, nanotechnologists dream of enabling these devices to make themselves.
Nanoscale self-assembly already happens, every instant, in living cells. These can be seen as collections of molecular cogs, motors and energy generators, programmed by DNA to organize themselves into a functioning unit.
As a result, many nanotechnologists have turned to DNA to direct their artificial components. The foundations for this latest research were laid in 1996 by a team from Northwestern University. These researchers showed that nanometre-sized gold crystals, tagged with strands of DNA, gather into clusters only when they encounter the right free-floating strands2.
The prospect of robotic devices replicating by building their own components has conjured up fearful images of a technological take-over -- most notably in a recent warning from Bill Joy, co-founder of Sun Microsystems. But these visions owe more to nanotechnology's excess of imagination than to present scientific realities.
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