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URSI: Hijacking Photosystem 2

When you stop to think about it, photosynthesis is actually quite a remarkable process. Plants capture sunlight—the most abundant energy source on our planet—and convert it into usable energy to support their own growth and development. While most plants convert the total amount of solar energy they receive with relatively low efficiency, some scientists believe that the plant system could be adapted and modified to increase this efficiency. In turn, this could lead to new strategies for solar photovoltaic panels, which currently have estimated efficiencies in the range of 12-30 percent.

“All grade school children know that plants produce oxygen,” says Chris Smart, associate professor of chemistry, “but what never seems to get taught is that the oxygen actually comes from water—H2O. During photosynthesis, the plant breaks the hydrogen-oxygen bond. After a number of steps, that oxygen is released into the atmosphere, and the hydrogen joins with CO2 to form sugars that the plant needs to grow. If the process can be interrupted in the first stages, there is a free electron available. And if we can move that electron around, that’s electric current.”

Scientists around the world are looking for ways to harness those “free” electrons with greater efficiency. Researchers at the University of Georgia have developed a process to capture these electron byproducts on a carbon nanotube structure and send them along a wire, thereby generating electrical current.

The problem is—it’s not very much current. Prof. Smart and his Undergraduate Research Summer Institute fellow, Drew Needleman ’16, are working on an idea that could change that exponentially.

“We’re working with photosystem 2—the protein complex in plants that catalyzes the reaction that splits H2O--and with carbon nanotubes that Professor Smart and Professor [Stuart] Belli developed,” says Needleman. “In very simple terms, what we plan to do is gold-plate the carbon nanotube structure, tether photosystem 2 to the gold, shine a light through it, and generate an electrical current.”

In essence, this is what the research team in Georgia has already accomplished.

The Needleman-Smart difference is this specialized carbon nanotube developed by Smart and Belli. “It’s been shown that by roughening the surface of the wire, you can produce more electricity,” says Smart. “That’s where our work comes in. Instead of just a wire or a roughened wire, we’ve produced an electrode that has carbon nanotubes on it. Envision a miniature version of a bristle brush with the carbon nanotubes being the bristles radiating out from this central wire, and each of those nanotubes is tipped with gold.”

Shown here are electron microscope images of these specialized carbon nanotubes. The bright, spherical shapes are the gold deposits, and the cylindrical or pipe-shaped objects are carbon nanotubes. “What we’re hoping is that we have here the ideal high-surface-area electrode upon which to tether photosystem 2,” says Smart.

Smart says that he wouldn’t normally have undertaken this project because he’s not a biochemist, but Needleman, who is majoring in biochemistry, talked him into it. “Professor Smart was my pre-major advisor,” says Needleman. “I’ve actually never taken a class with him, but I’ve been doing research with him on fullerenes and also hops, and I convinced him that I had the molecular biology skills to do the protein cloning and purification.”

The first part of the project was to grow enough of the photosystem 2 protein complex to be able to extract the genome. “Photosystem 2 has very specific growing conditions,” says Needleman. “It needs to be grown at a particular temperature under constant illumination with constant shaking, and the air needs to be saturated with water and 3% carbon dioxide.” During the first few weeks of URSI, Needleman built an incubator using old, discarded equipment to meet those requirements and on the day of this interview harvested his first batch of cells.

“Today I did about six hours of pipetting and centrifuging and extracted the genome,” he says. “It wasn’t until about two hours ago that I knew whether or not a month’s worth of work paid off. It was stressful.”

But it did pay off. Now Needleman will genetically modify the protein prior to purifying it. He doesn’t expect to complete the project by the end of URSI. “If I can say by the end of the summer that my cells are capable of making the protein I want, I will be happy,” he says. “It’s going to be my senior project. I expect to lose a lot of sleep over this. But if I can get it done by January, I’ll be thrilled.”

And if all goes according to plan, says Smart, “Drew will be presenting with me at the Electrochemical Society meeting next May.”

--Julia Van Develder

Posted by Office of Communications Monday, July 27, 2015