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Micro-motors powered by
DNA
Bell Labs animation
explains how the DNA tweezers
work.
At Lucent's
Bell Labs, physicist Bernard Yurke loads synthesized DNA into
vials. The DNA assembles into motorized tweezers within these
vials.
By Alan Boyle
MSNBC
In an
experiment that could help set the stage for future generations of
miniaturized computers, DNA molecules have been engineered to serve as
both the moving parts and the fuel for machines measuring mere billionths
of a meter long.
THE NEWLY
REVEALED experiments, conducted at Lucent Technologies’ Bell Labs and
detailed in Thursday’s issue of the journal Nature, involve creating
“motorized tweezers” out of three strands of specially constructed DNA
molecules.
But don’t expect to pick up a
pair of these tweezers at the drugstore anytime soon. Instead, the
researchers suggest more sophisticated applications: to investigate the
interaction of chemically active components attached to the ends of the
tweezers; to serve as information carriers for molecular-scale machines;
or to assemble such machines by following a series of coded
instructions.
If you could attach the DNA
strands to molecules that conduct electricity, you just might be able to
create superminiaturized circuitry, said Bell Labs physicist Bernard
Yurke, who led the research team.
“The idea behind building more powerful computers is based on how we
assemble these things,” Yurke told MSNBC. “We just throw these strands of
DNA into a test tube, they diffuse around, find each other and assemble
themselves into these tweezers. What we would like is to do this kind of
assembly on a much larger scale.”
Bell Labs
scientists already are working on this concept, he said.
Molecular computing could yield a huge payoff, since it takes
less than a trillionth of a second for an electron to hop from one
molecule to another. “One is talking about time scales that are roughly
1,000 times faster than the clock speeds of the current generation of
PCs,” Yurke said. Huge amounts of memory or processing power could be
packed in a small space.
NATURAL COMPUTERS
In a sense,
molecules of DNA are already natural “computers” that process the data of
life within the cells of every organism. The complementary pairs of bases
— adenine and
thymine, guanine and cytosine — can encode thousands of bits
of information in a long, double-spiral of chemical bonds.
Over the past few years, scientists have used the
regular, controllable architecture of DNA for new purposes: to guide the
fabrication of nanocircuitry and even create molecular
switches.
The tweezers created by Bell
Labs demonstrate that DNA molecules can be “programmed” to move in a
precise way.
During the operation, the ends
of the molecular tweezers move about 6 billionths of a meter — a distance
so small that the researchers had to use a complex technique involving
fluorescent dye to determine whether the molecules were flexing the way
they hoped.
HOW IT WORKS
STEP 1: The bent "tweezers"
strand of DNA is shown in dark blue. It's linked up with two other longer
strands, colored red and green. Those strands provide the key for closing
the ends of the tweezers.
Yurke said the idea had its origins in the observations of how molecular motors work
within living cells. Those motors use proteins such as kinesin
and myosin, but Yurke turned instead to DNA, inspired by the work of
researchers such as New York University’s Nadrian
Seeman.
At first Yurke and his colleagues chose DNA sequences at
random, and they eventually found that one sequence formed a type of
tweezers, or hairpin.
“When we added the
other strands that it was supposed to interact with, it could open up that
hairpin,” he recalled. “We found that strands of DNA could be used to
induce configuration changes in other strands of DNA, and that was the
‘aha’ moment.”
STEP 2: The white strand is
known as the "fuel strand." It binds to each of the tails hanging down
from the tweezers, drawing the arms closer together. ...
Each side of the Bell Labs molecular tweezers has an extra
tail of DNA hanging down. To close the tweezers, a specially designed
“fuel strand” of DNA is introduced that links up with both tails, drawing
the molecule together like the sides of a zipper.
“Energy is released as the base pairs bind,” Yurke said. “When the
strand interacts with the arms, the system is basically going downhill
energetically.”
The thermodynamic change is
what makes the tweezers a type of molecular motor, he said.
STEP 3: The "fuel strand" is
fully bonded with the tails, and the dark blue tweezers is in the closed
position. But notice the extra bases hanging down from the right side of
the fuel strand: Another specially designed piece of DNA can bind to that
end and pull the fuel strand away. That allows the tweezers to relax and
open again.
“Typically when we’re doing our experiments, we have a vial
containing something like 30 trillion of these tweezers,” Yurke said. When
the fuel strands are added to the solution, it takes about 10 seconds for
half of those trillions of chemical tweezers to close, he said.
To open the tweezers again, yet another special strand
of DNA is added to the solution. This removal strand latches onto the free
end of the fuel strand, beginning a tug-of-war with the
tweezers.
“It’s a competition,” Yurke said,
but the extra bonds give the removal strand an advantage. Within a
fraction of a second, the fuel strand is pulled loose from the tweezers,
freeing both ends to open again.
THE ROAD AHEAD
Yurke said researchers still had to address some major challenges in
order to clear the way for molecular-scale manufacturing.
Yurke is concentrating on how to attach DNA tags to
molecular-scale electronic components. DNA assembly has to be done in a
water solution — which limits the kinds of chemicals that can be used. And
Yurke said chemists haven’t yet found any suitable molecules that can
behave like transistors.
However, he voiced
confidence that the challenges would be met.
“We will find molecules that can do the kind of job we would like
them to do,” he said.
Yurke’s colleagues in the Nature research are Allen P.
Mills Jr. and Friedrich C. Simmel of Lucent Technologies’ Bell Labs,
Jennifer L. Neumann of Rutgers University, and Andrew J. Turberfield of
the University of Oxford, who participated in the project during a
sabbatical at Bell Labs.
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