What's New in Innovation?

EFRC researchers construct an artificial version of a bacterium’s light-absorbing ‘antenna’

By Diana Lutz

dividing cells of green sulfur bacterium
Image courtesy of Martin Hohmann-Marriott and Robert Blankenship

Electron microscopic tomogram of dividing cells of the green sulfur bacterium Chlorobaculum tepidum, with chlorosomes rendered in simulated color.

Sometimes when people talk about solar energy, they tacitly assume that we’re stuck with some version of the silicon solar cell and its technical and cost limitations.

Not so.

The invention of the solar cell, in 1941, was inspired by a newfound understanding of semiconductors, materials that can use light energy to ultimately create an electrical current.

Silicon solar cells have little in common with the biological photosystems in tree leaves and pond scum that use light energy to ultimately create sugars and other organic molecules.

At the time, nobody understood these complex assemblages of proteins and pigments well enough to exploit their secrets for the design of solar cells.

But things have changed.

At Washington University in St. Louis’s Photosynthetic Antenna Research Center (PARC), scientists are exploring biological photosystems to build both hybrids that combine natural and synthetic parts as well as fully synthetic versions of natural systems. PARC is one of 46 Energy Frontier Research Centers (EFRCs) established by the DOE Office of Science in 2009 at universities, national laboratories, and other institutions around the nation to accelerate advanced basic research related to energy.

The PARC team has just succeeded in making a crucial photosystem component – a light-harvesting antenna – from scratch. The new antenna is modeled on the chlorosome, or biological antenna, found in green photosynthetic bacteria.

Chlorosomes are giant assemblies of pigment molecules. Perhaps nature’s most spectacular light-harvesting antennae, they allow green bacteria to photosynthesize even in the dim light of the deep ocean.

Dewey Holten, professor of chemistry at Washington University, and collaborator Christine Kirmaier, research professor of chemistry, are part of a team that is trying to make synthetic chlorosomes. Holten and Kirmaier use ultra-fast laser spectroscopy and other analytic techniques to follow the rapid-fire energy transfers in photosynthesis. The team’s results are described in the New Journal of Chemistry.

Next Steps
Although this project focused on self-assembly, the PARC scientists have already taken the next step toward a practical solar device. “With Pratim Biswas, the Lucy and Stanley Lopata Professor and Chair of the Department of Energy, Environmental & Chemical Engineering at Washington University, we’ve since demonstrated that we can get the pigments to self-assemble on surfaces, which is the next step in using them to design solar devices,” said Holten.

“We’re not trying to make a more efficient solar cell in the next six months,” Holten cautions. “Our goal instead is to develop fundamental understanding so that we can enable the next generation of more efficient solar powered devices.”

As biological knowledge has exploded in the past 50 years, mimicking nature has become a smarter, more realistic strategy. While biomimicry hasn’t always worked as in the case of designing early flying machines, biomimetic or biohybrid designs already have solved significant engineering problems in other areas and promise to greatly improve the design of solar- powered devices as well.

After all, nature has had billions of years to experiment with ways to harness the energy in sunlight for useful work.

—Diana Lutz, Washington University in St. Louis, dlutz@wustl.edu

Reprinted with permission by the U.S. Department of Energy Office of Science. To read the entire article, go to: http://science.energy.gov/stories-of-discovery-and-innovation/127025/.

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