New
approach is a promising first step toward the development of tiny devices that
harvest electrical energy from everyday tasks
Imagine charging your phone as you walk,
thanks to a paper-thin generator embedded in the sole of your shoe. This
futuristic scenario is now a little closer to reality. Scientists from the U.S.
Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab)
have developed a way to generate power using harmless viruses that convert
mechanical energy into electricity.
The scientists tested their approach by
creating a generator that produces enough current to operate a small
liquid-crystal display. It works by tapping a finger on a postage stamp-sized
electrode coated with specially engineered viruses. The viruses convert the
force of the tap into an electric charge.
Their generator is the first to produce
electricity by harnessing the piezoelectric properties of a biological
material. Piezoelectricity is the accumulation of a charge in a solid in
response to mechanical stress.
The milestone could lead to tiny devices
that harvest electrical energy from the vibrations of everyday tasks such as
shutting a door or climbing stairs.
It also points to a simpler way to make
microelectronic devices. That’s because the viruses arrange themselves into an
orderly film that enables the generator to work. Self-assembly is a much sought
after goal in the finicky world of nanotechnology.
The scientists describe their work in a
May 13 advance online publication of the journal Nature Nanotechnology.
“More research is needed, but our work
is a promising first step toward the development of personal power generators,
actuators for use in nano-devices, and other devices based on viral
electronics,” says Seung-Wuk Lee, a faculty scientist in Berkeley Lab’s
Physical Biosciences Division and a UC Berkeley associate professor of
bioengineering.
He conducted the research with a team
that includes Ramamoorthy Ramesh, a scientist in Berkeley Lab’s Materials
Sciences Division and a professor of materials sciences, engineering, and
physics at UC Berkeley; and Byung Yang Lee of Berkeley Lab’s Physical
Biosciences Division.
The piezoelectric effect was discovered
in 1880 and has since been found in crystals, ceramics, bone, proteins, and
DNA. It’s also been put to use. Electric cigarette lighters and scanning probe
microscopes couldn’t work without it, to name a few applications.
But the materials used to make
piezoelectric devices are toxic and very difficult to work with, which limits
the widespread use of the technology.
Lee and colleagues wondered if a virus
studied in labs worldwide offered a better way. The M13 bacteriophage only
attacks bacteria and is benign to people. Being a virus, it replicates itself
by the millions within hours, so there’s always a steady supply. It’s easy to
genetically engineer. And large numbers of the rod-shaped viruses naturally
orient themselves into well-ordered films, much the way that chopsticks align
themselves in a box.
These are the traits that scientists
look for in a nano building block. But the Berkeley Lab researchers first had
to determine if the M13 virus is piezoelectric. Lee turned to Ramesh, an expert
in studying the electrical properties of thin films at the nanoscale. They
applied an electrical field to a film of M13 viruses and watched what happened
using a special microscope. Helical proteins that coat the viruses twisted and
turned in response—a sure sign of the piezoelectric effect at work.
Next, the scientists increased the
virus’s piezoelectric strength. They used genetic engineering to add four
negatively charged amino acid residues to one end of the helical proteins that
coat the virus. These residues increase the charge difference between the
proteins’ positive and negative ends, which boosts the voltage of the virus.
The scientists further enhanced the
system by stacking films composed of single layers of the virus on top of each
other. They found that a stack about 20 layers thick exhibited the strongest
piezoelectric effect.
The only thing remaining to do was a
demonstration test, so the scientists fabricated a virus-based piezoelectric
energy generator. They created the conditions for genetically engineered
viruses to spontaneously organize into a multilayered film that measures about
one square centimeter. This film was then sandwiched between two gold-plated
electrodes, which were connected by wires to a liquid-crystal display.
When pressure is applied to the
generator, it produces up to six nanoamperes of current and 400 millivolts of
potential. That’s enough current to flash the number “1” on the display, and
about a quarter the voltage of a triple A battery.
“We’re now working on ways to improve on
this proof-of-principle demonstration,” says Lee. “Because the tools of
biotechnology enable large-scale production of genetically modified viruses,
piezoelectric materials based on viruses could offer a simple route to novel
microelectronics in the future.”
Berkeley Lab’s Laboratory Directed
Research and Development fund and the National Science Foundation supported
this work.
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Lawrence Berkeley National Laboratory
addresses the world’s most urgent scientific challenges by advancing
sustainable energy, protecting human health, creating new materials, and
revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s
scientific expertise has been recognized with 13 Nobel prizes. The University
of California manages Berkeley Lab for the U.S. Department of Energy’s Office
of Science. For more, visit www.lbl.gov.
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