http://arstechnica.com/news.ars/post/20080818-using-viruses-to-build-self-assembled-nanoscale-batteries.html
Using viruses to build self-assembled nanoscale batteries
By John Timmer | Published: August 18, 2008 - 04:00PM CT
The lithography techniques we rely on to give us the latest in
electronics are getting more expensive and technically challenging with
each new process shrink. A number of researchers are now looking into
whether we can solve some of the problems by turning to biology.
Biological systems self-assemble into complex, ordered structures on the
nanometer scale, all at room temperature and with cheap ingredients. The
latest development in biology-based circuity comes courtesy of
researchers at MIT who have crafted a battery with an anode wired-up
using a virus. But that's probably not even the best part—these
nanoscale batteries can be printed onto most conducting surfaces.
The battery is described in a publication that The Proceedings of the
National Academies of Science will release later this week. It's the
latest work from Angela Belcher, who has been laying the groundwork for
viral-driven electronics assembly for a while now. Her lab's virus of
choice, M13, is only capable of attacking bacteria. The virus is a
filamentous structure hundreds of nanometers long, but only 6.5nm in
diameter—smaller than the finest electronics features currently in use.
The virus' coat of proteins self-assembles from thousands of identical
proteins, which allows researchers to manipulate the protein structure
in order to allow the virus to serve as a template for other materials.
In this case, a few tweaks to the protein's sequence allowed it to
interact with cobalt oxides, which can function as anodes in
lithium-based batteries.
But an anode is only part of a functional battery. The new paper
describes a process that allows the battery components to largely
self-assemble. The researchers built a template of polydimethylsiloxane
that contained round posts roughly five microns in diameter. On top of
the post, they deposited a dozen alternating layers of two solid
electrolytes: polyethlenimine and polyacrylic acid. These layers formed
a cap on the substrate about 150nm thick. On top of that, the
researchers deposited the M13 virus, dipped in a cobalt oxide solution
that converted the viral layer into the nanobattery's anode.
To get access to any charge stored in this battery, however, it needs to
be wired up to a larger conducting device. Fortunately, the solid
electrolytes don't adhere to the substrate well, which allowed the
researchers to simply "print" the batteries on a conducting surface; a
flat platinum electrode, in this case. This printing stamped multiple
batteries down on the surface of a single electrode.
The authors ran several of these systems in a series, with a cathode
provided by a bit of lithium-covered copper. Once dipped in a
lithium-based solution, they were able to run the system through
repeated cycles of charging and discharging. Less than a centimeter's
worth of the batteries managed to hold anywhere from 375 to 460 nAh,
depending on the charging conditions.
The authors note that these batteries can be stamped pretty much
anywhere on a conducting surface, including flexible ones. They're
currently at work trying to figure out how to incorporate a cathode into
their production technique. These batteries aren't likely to be
solutions for big problems, like laptop batteries, but they could find a
niche in the world of miniaturized, low-power devices.
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