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July 2012, Week 1

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Mon, 2 Jul 2012 00:33:41 -0400
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Can Evolution Make the Next Generation of Computer Chips?
By Joseph Stromberg
Smithsonian Magazine
June 28, 2012
http://blogs.smithsonianmag.com/science/2012/06/can-evolution-make-the-next-generation-of-computer-chips/

In 1965, Intel co-founder Gordon Moore made a prediction
about computing that has held true to this day. Moore's
law, as it came to be known, forecasted that the number
of transistors we'd be able to cram onto a circuit-and
thereby, the effective processing speed of our
computers-would double roughly every two years.
Remarkably enough, this rule has been accurate for
nearly 50 years, but most experts now predict that this
growth will slow by the end of the decade.

Someday, though, a radical new approach to creating
silicon semiconductors might enable this rate to
continue-and could even accelerate it. As detailed in a
study published in this month's Proceedings of the
National Academy of Sciences, a team of researchers from
the University of California at Santa Barbara and
elsewhere have harnessed the process of evolution to
produce enzymes that create novel semiconductor
structures.

"It's like natural selection, but here, it's artificial
selection," Daniel Morse, professor emeritus at UCSB and
a co-author of the study, said in an interview. After
taking an enzyme found in marine sponges and mutating it
into many various forms, "we've selected the one in a
million mutant DNAs capable of making a semiconductor."

In an earlier study, Morse and other members of the
research team had discovered silicatein-a natural enzyme
used used by marine sponges to construct their silica
skeletons. The mineral, as it happens, also serves as
the building block of semiconductor computer chips. "We
then asked the question-could we genetically engineer
the structure of the enzyme to make it possible to
produce other minerals and semiconductors not normally
produced by living organisms?" Morse said.

To make this possible, the researchers isolated and made
many copies of the part of the sponge's DNA that codes
for silicatein, then intentionally introduced millions
of different mutations in the DNA. By chance, some of
these would likely lead to mutant forms of silicatein
that would produce different semiconductors, rather than
silica-a process that mirrors natural selection, albeit
on a much shorter time scale, and directed by human
choice rather than survival of the fittest.

The original enzyme was taken from marine sponges, which
use it to make their silica skeletons. Photo via
Wikimedia Commons/Hannes Grobe

To figure out which mutated forms of the silicatein DNA
would lead to the desired semiconductors, the DNA needed
to be expressed through a cell's molecular machinery.
"The problem was that, although silica is relatively
harmless to living cells, some of the semiconductors
that we want to produce would be toxic," Morse said. "So
we couldn't use living cells-we had to use a synthetic
surrogate for cells." As an artificial replacement for
cells, the team used tiny bubbles of water formed around
plastic beads. A different form of the marine sponge DNA
was attached to each of the millions of beads, and the
chemicals necessary for the DNA to be expressed as an
enzyme were included in the water.

Next, the plastic bead "cells" were encased in oil,
which acted as an artificial cell membrane. The beads
were then put in a solution that included the chemicals
(silicon and titanium) needed for the mutant enzymes to
start building semiconductor minerals on the outside of
the beads.

After allowing some time for the enzymes to do the work
of making minerals, the beads were passed through a
laser beam, next to a sensor that automatically detected
when either of the desired semiconductors (silicon
dioxide or titanium dioxide) passed through. Afterward,
the successful beads-those that had these semiconductors
accumulated on their outsides-were broken open so the
mutant DNA could be isolated and its effect could be
confirmed.

Various forms of silicon dioxide are currently used in
the production of computer chips, while titanium dioxide
is used in manufacturing solar cells. The production of
substances like these using biological enzymes and
directed evolution is a first.

While this certainly doesn't mean that the researchers
had cells pumping out computer chips, it does point to a
new method of creating semiconductors. The
semiconductors made by the mutant enzymes in the
experiment, Morse said, "have never before been produced
in nature, and have never before been produced by an
enzyme, but they're presently used in industry for all
kinds of communications and information processing." A
few years down the road, new and specialized forms of
semiconductors produced using this method could even
play a role in ensuring Gordon Moore's prediction stays
true.

___________________________________________

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