SPINACH MAY SOON POWER MOBILE DEVICES

From: Dr. Jai Maharaj (usenet_at_mantra.com)
Date: 09/26/04 

Date: Sun, 26 Sep 2004 20:08:25 GMT

SPINACH MAY SOON POWER MOBILE DEVICES

Forwarded message from fidyl@yahoo.com

[ Subject: Spinach May Soon Power Mobile Devices
[ From: fidyl@yahoo.com
[ Date: Sat, 25 Sep 2004

Spinach May Soon Power Mobile Devices

September 16, 2004

http://www.physorg.com/news1181.html

For the first time, MIT researchers have incorporated a
plant's ability to convert sunlight to energy into a
solid-state electronic "spinach sandwich" device that may
one day power laptops and cell phones.

At the heart of the device is a protein complex dubbed
Photosystem I (PSI). Derived from spinach chloroplasts,
PSI is 10 to 20 nanometers wide. Around 100,000 of them
would fit on the head of a pin. "They are the smallest
electronic circuits I know of," said researcher Marc A.
Baldo, assistant professor of electronic engineering and
computer science at MIT.

Image: A protein complex named Photosystem I, which is
derived from spinach chloroplasts, functions as an
extremely small electronic circuit. About 100,000 of them
would fit on the head of a pin.

Baldo and other researchers from MIT, the University of
Tennessee and the U.S. Naval Research Laboratory,
including electrical and biomedical engineers,
nanotechnology experts and biologists, collaborated on
the world's first solid-state photosynthetic solar cell.
The work was reported in NanoLetters, a publication of
the American Chemical Society.

"We have crossed the first hurdle of successfully
integrating a photosynthetic protein molecular complex
with a solid-state electronic device," Baldo said.

Plants' ability to generate energy has been optimized by
evolution, so a spinach plant is extremely efficient,
churning out a lot of energy relative to its size and
weight. But combining biological and non-biological
materials in one device has stymied researchers in the
past. Biological materials need water and salt to survive
 -- both are deadly for electronics.

-From wet to dry

A new twist in the current work is a membrane of peptide
surfactants -- similar to the main ingredient in soap --
that helped the photosynthetic complexes self-assemble
and stabilize while the circuit was fabricated.

So far, scientists and engineers' efforts to harness the
photosynthetic properties of green plants have been most
successful with naturally soft organic materials in
liquid solutions. But if organic solar cells are to be
practical for commercial devices, they need to be
integrated with solid-state electronics.

The researchers ground up ordinary spinach and purified
it with a centrifuge to isolate a protein deep within the
cell.

The resulting dark green pellets that smell like cut
grass were purified still further and coaxed into a
water-soluble state. One of the challenges was to keep
the proteins in the same configuration as they appear
naturally in the organism.

Here's where peptides come in. The 80,000-plus kinds of
proteins in our body, when in fragments called peptides,
transform themselves like tiny LEGOs(TM) into millions of
substances. Shuguang Zhang, associate director of MIT's
Center for Biomedical Engineering, discovered that these
same peptides can be tweaked into forming completely new
natural materials that perform useful functions. One of
his designer nanomaterials, which acts like the main
ingredient in soaps and detergents, turns out to be ideal
for keeping protein complexes functional on a cold, hard
surface.

The spinach-sandwich device has no water. Proteins
usually need water to survive, but using Zhang's
detergent peptide, the researchers were able to stabilize
the protein complexes in a dry environment for at least
three weeks. "Detergent peptide turned out to be a
wonderful material to keep proteins intact on the surface
with electronics," Zhang said. He speculates that the
detergent material has some water trapped within it,
similar to the way plant seeds hoard oils that maintain
the seeds' integrity in dry conditions.

Building the sandwich

The bottom layer of the molecular electronic device is
transparent glass coated with a conductive material. A
thin layer of gold helps the chemical reaction that
assembles the spinach chlorophyll Photosystem I
complexes. The researchers then evaporate a soft organic
semiconductor that prevents electrical shorts and
protects the protein complexes from the layer of metal
that completes the sandwich.

The researchers shone laser light on the device to create
optical excitation, then measured the resulting current.
"An important caveat is that we got very little current
out, mostly because we had just a thin layer of the
complexes in our devices," Baldo said. "Most of the
optical excitation passed straight through without being
absorbed. Of the light that was absorbed, we estimate
that we converted around 12 percent to charge."

The researchers hope to achieve a power conversion
efficiency of 20 percent or more (which would provide an
extremely efficient power source) by creating multiple
layers of PSI or assembling them on rough surfaces or 3-D
surfaces, like skyscrapers that concentrate a huge amount
of surface area within a relatively small space.

Patrick J. Kiley (S.B. 2003) of MIT also worked on this
research, which is funded by the Defense Advanced
Research Projects Agency, the Air Force Office of
Scientific Research, and the National Science Foundation.

Source - MIT

End of forwarded message from fidyl@yahoo.com

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Relevant Pages

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