Spinach Power for Integrated Circuits and Fuel Cells
ate spinach leaves for strength. Now researchers at Oak Ridge
National Laboratory in Tennessee are using microscopic spinach
proteins for electronic devices. Spinach leaves are put in a blender
and processed down to microscopic proteins called chloroplasts
that convert light into chemical energy. The next step is a scientific
breakthrough first done by physicist Dr. Elias Greenbaum at the
Oak Ridge National Lab. He puts the spinach proteins into a platinum
solution to get a metal coating. This marriage between the plant
and mineral world could make silicon chips obsolete in another
ten years. I asked Dr. Greenbaum why spinach?
is an easy plant to work with. All plants essentially convert light
energy to chemical energy by about the same mechanism. There are
2 photosynthesis reaction centers 2 parts of the plant that
capture light energy. And the energy contained in the light gets
converted into electrical energy before the plants finally transform
it to chemical energy. So, the valuable product of plants can be
thought of in 2 ways:
is stable chemical molecules such as starch which is the food
stuff that we eat.
is the electrical energy which appears before the chemical energy
is produced. We're interested in working on both of those aspects
how plants convert light into electrical energy and into
example, in the case of chemical energy, we would like to use green
plants to split water to molecular hydrogen and oxygen there
the energy-rich product is hydrogen and that could be used in a
fuel cell to make electricity. Or we can tap in earlier in the chemical
and physical processes before the chemical energy is made
earlier step of the creation of electrical energy. And that could
be used to make molecular electronic devices.
I THINK OF A SPINACH LEAF, I CAN SEE THAT DEEP GREEN WITH PURPLE
VEINS. WHAT IS IT THAT YOU ARE ACTUALLY GETTING FROM THE LEAVES
TO USE IN THIS ELECTRONIC RESEARCH?
suppose we do a fantastic voyage type experiment where we go into
the leaf and magnify the surroundings. The size of the leaf, say
on a bush or tree, typically might be a tenth of a meter. Imagine
magnifying the leaf one billion times 1,000,000,000.
will bring you down to the molecular scale. If you could walk around
the leaf at that molecular scale and look at the membrane now on
a nanometer scale — nano means 1/1 billionth of a meter — that typically
is the size of molecules in membranes where all of the useful work
of photosynthesis is being done for the conversion of light energy
into chemical energy.
you could look at the membranes which is what electron microscopes
do and that's how I'm able to tell you what the description is
you would see molecular structures. These are small structures made
up of proteins that capture light energy and do the first step in
converting light energy into chemical energy. That first step is
the ejection of an electron the electron is one of the parts
of the molecule the ejection of the electron from one side
of the membrane to the other. That ejection of the electron is the
separation of electrostatic charges. So, the electron that has a
negative charge moves to the far side of the membrane leaving behind
a positive charge. That plus/minus charge operation is a creation
of electrostatic potential energy. And that's the first step in
the creation of chemical energy from light energy.
what we do is we have methods for extracting the molecular components
from that membrane and then purifying them using standard biochemical
techniques. So you have purified amounts of these key photosynthetic
reaction centers that are essentially little molecular photovoltaic
devices they are like little silicon cells. When a photon
is absorbed in the reaction center, it triggers this charge separation
and it creates an electrical potential or a voltage. That source
of energy is what drives the energy rich products of photosynthesis.
WHAT YOU'RE DOING IS ESSENTIALLY GOING DOWN TO THE MOLECULAR LEVEL
IN THE SPINACH LEAF LOOKING FOR THESE PROTEIN CENTERS THAT ARE INVOLVED
WITH TAKING IN PHOTON ENERGY AND RELEASING ELECTRONS?
Now, the recent discovery that we've made curiously this
one discovery of the molecular electronic properties actually does
not relate directly to the light absorbing properties. We've shown
that these there are two discoveries that we've made: one
is after we've extracted and purified these photo system reaction
centers the one we work with is called Photo System One.
It's one of the two reaction centers in photosynthetic tissue.
THESE ARE PROTEINS?
are pigment protein complexes. It's protein into which a chlorophyll
is imbedded. So the green color that you see in plants is largely
the chlorophyll pigments. That chlorophyll pigment is imbedded into
a protein scaffold so that the chlorophyll molecules are held in
precise positions, locations and orientations in the membrane. That's
why the work of photosynthesis can be done.
IS IT THE CHLOROPHYLL MOLECULE ITSELF THAT IS UNIQUE IN TAKING IN
PHOTON ENERGY AND RELEASING ELECTRONS?
one out of every 300 chlorophyll molecules has that unique property.
If you look at a plant and spinach is no exception
most of that chlorophyll is not doing the electron transfer reaction
that I mentioned earlier. For every one that actually does that
special ejection of an electron across the membrane, there are 200
to 300 chlorophyll molecules whose only purpose is to act like an
antennae to capture light from the sun. It's like holding an umbrella
upside down in the rain where if the umbrella is opened up, the
bigger the umbrella, the more rain drops you'll capture. But all
of those raindrops get funneled to the bottom of the umbrella. And
the bigger the umbrella, the more drops it can capture in a given
amount of time. That's how the chlorophyll molecules work in the
plant. There are about 200 to 300 of those chlorophyll molecules
that catch the photon. And then they sort of do a relay race, tag
team match, where the photon gets handed from chlorophyll molecule
to chlorophyll molecule to where finally it hits the magic chlorophyll
the reaction center chlorophyll and KABOOM!
the charge transfer takes place. That's where we come in. We try
to capture that. But what we've shown in that reaction center (and
the discovery we reported at the Centennial Meeting of the American
Physical Society) is that the reaction centers can be oriented on
a 2-dimensional surface. Now, remember they have been removed from
the spinach leaf. There is no more spinach now when we're working
with it. It's just reaction centers and pigment protein complexes.
WILL RELEASE ELECTRONS.
right. If you look at them in solution, you can see the green color.
But of course, they are much too small to see the individual ones
because they are only 5 nanometers or 5 billionths of a meter.
But we have studied these with a technique called scanning tunneling
spectroscopy where we can measure the properties of single photosynthetic
reaction centers. And we've discovered that they can be oriented
on a 2-dimensional surface if that surface is chemically prepared
in a correct way. And also that they behave like little diodes
rectification junctions. In other words, a diode is an electronic
component. And what it does is to conduct electricity easily in
one direction, but with difficulty in the opposite direction. So,
it's a rectifier. And we have shown that the photosynthetic reaction
center behaves like a molecular rectifier or a molecular diode.
So that is a genuine molecular component that could be used in the
construction of other molecular components.
ELECTRONS ONE WAY?
That is a standard component that you find in molecular circuits.
Now, if you take that molecular diode and put it in conjunction
with small scale molecular resistors, you begin to have the first
steps of constructing molecular logic devices which are the elementary
building blocks of computers. So, that's sort of where we're going,
but we're no where near there. That's sort of the logic and rationale
of where our work is pointing. We would like to be able to construct
logic devices from these molecular structures.
MUCH SMALLER WOULD THE SPINACH PROTEIN ENERGY FACTORIES, WE'LL CALL
THEM, BE COMPARED TO WHAT AN INTEL PENTIUM CHIP RIGHT NOW IS WORKING
you give me the advantage of a wish list and say we can do the best
that theoretically we could do then we'd be talking about
a factor of 100 to a 1000.
MEAN YOU COULD MAKE THINGS THAT MUCH SMALLER?
that much smaller because of the structures. But that's only the
idealized situation. It's sort of a wish list situation. It's sort
of the rationale for moving in that direction. There is another
factor we should keep in mind also . . . that conventional silicon
lithography those guys can do great things. Don't get me
wrong. It's really wonderful what can be done with conventional
IS HOW THEY MAKE THESE INTEL CHIPS?
yeah. But the cost of getting smaller and smaller keeps increasing.
The smaller you want to go, the greater is the capital investment
in the facility that is needed to make them. So, what we're hoping
is that a fundamentally different philosophy in the approach we
are taking that is, we would like to use the technique of
directed self-assembly, directed molecular self-assembly such that
these microscopic structures essentially assemble themselves in
very much the same way that biological systems assemble themselves.
The fact that living systems exist is the best proof that bio-technology
on the nanometer scale actually works . . . because those reaction
centers that I mentioned earlier in the photosynthetic membranes
are very much identical to the way molecular structures are imbedded
in all biological membranes. They self-assemble and they orient
and they do their job in a spontaneous way. So that's the approach
that is fundamentally different philosophically we would
like to use this technique for directed self-assembly and avoid
this high energy, high intensive, high capital intensive process
for constructing devices.
IT SOUNDS AS IF YOU ARE DESCRIBING A TECHNOLOGY IN THE NEAR FUTURE
IN WHICH THERE WILL BE INCREASING COMBINATIONS OF WHAT WE MIGHT
CALL THE MINERAL-MATTER WORLD AND THE BIOLOGICAL WORLD.
In fact, one of the aspects of our work we were the first
to show that we could make direct electrical contact with the electron
I referred to earlier that gets ejected from the Photo System One
Reaction Center. We've actually discovered methods to precipitate
metallic platinum right onto the surface of the photosynthetic membrane
where the electrons emerge. And we've made electrical contact with
those electrons and we can catalytically evolve molecular hydrogen
because the platinum metal cluster is a good catalyst for hydrogen
evolution. So, that discovery is an example of what you are talking
about. It's sort of this composite new properties that are
endowed to material that is derived from biological material. In
this case, it is spinach membranes and the new property is useful
and one which did not exist before namely, the possibility
of splitting water to molecular hydrogen and oxygen under the influence
IF I UNDERSTAND CORRECTLY, YOU WOULD HAVE THE SPINACH PROTEIN ENERGY
FACTORIES COATED WITH A THIN LAYER OF PLATINUM THAT THEN HAS A CATALYTIC
FUNCTION OF PRODUCING HYDROGEN AND OXYGEN . . .
SO YOU COULD THEN TAKE THE PLANTS COMBINED WITH THE PLATINUM AND
CREATE FUEL CELLS TO PROVIDE ENERGY?
would produce hydrogen which in turn could be used in fuel cells
to make electricity. And that's a carbon-neutral process for energy
WOULD BE NO CARBON POLLUTION.
net production of carbon dioxide.
HOW FAR INTO THE FUTURE REALISTICALLY DO YOU THINK YOUR CURRENT
RESEARCH AND DEVELOPMENT HAS TO GO BEFORE WHAT WE'VE JUST DISCUSSED
WOULD BE WORKING IN THE WORLD AROUND US?
I think it's important to understand that this is all fundamental
science that we're studying right now. But it is fundamental science
with a mission towards solving a practical problem. So, I think
we are at least five or ten years in the fundamental science stage
of developing the limiting aspects of hydrogen production, of understanding
the molecular structures of the photosynthetic membranes for constructive
molecular electronic devices. I think we are looking at 5 to 10
years of largely laboratory based fundamental research before we'll
have enough information to understand what the next step is in practical
YOU DISCOVERED ANY KIND OF PROBLEMS WITH INTERFACING THESE BIOLOGICAL
PROTEINS WITH METALLIC MOLECULES?
sure. That is one of the focus areas of our research. Essentially
wiring these molecules together. There is no easy way to do that
now. The ability to wire molecules on a wide scale basis and to
get them to function in a reliable way.
THERE SOME NATURAL RESISTANCE BETWEEN THE ORGANIC MOLECULES IN THE
SPINACH PLANT AND THE METALLIC MOLECULES OF THE PLATINUM?
they need not be. It depends upon the chemistry of interaction between
the pigment protein complexes of the photosynthetic reaction centers
and the chemical species that is used to convert or produce the
precipitation of metal. So by understanding these surface chemistries
between the bio world and the inorganic bio world, compatibility
can be achieved between them.
YOURS THEN THE VERY FIRST DISCOVERY RELATED TO BEING ABLE TO PUT
THE PLATINUM COATING ON THE PROTEINS?
Info: Dr. Greenbaum's spinach/platinum work is funded by the Office
of Basic Energy Sciences and Office of Energy Efficiency and Renewable
Energy in the U. S. Department of Energy. The Dept. of Energy
has contracted Lockheed-Martin to manage Oak Ridge National Laboratory.
© 2001 Linda Moulton Howe All Rights Reserved. Republication and redissemination
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