Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

lundi 28 juin 2004

In "Could laptops run on spinach?," Nature reports that researchers from the MIT have made solar cells powered by spinach proteins. These prototype solar cells which transform light into 'green' energy could be used one day to coat and power your laptop. There is still work to be done before becoming a commercial product. Right now, the prototype delivers current for only three weeks. And they are not very efficient, converting only 12% of the light they absorb into electricity. However, these spinach-powered solar cells are better for our environment than silicon solar cells. And according to Science News Online, in "Protein Power: Solar cell produces electricity from spinach and bacterial proteins," they also have the potential to be self-repairing.

Let's start with Nature.

The biologically based solar cells, which convert light into electrical energy, should be efficient and cheap to manufacture, says co-creator Marc Baldo of the Massachusetts Institute of Technology. They could even be used to coat and power laptops, providing a portable source of green energy.
Baldo's team isolated a variety of photosynthetic proteins from spinach and sandwiched them between two layers of conducting material. When light was shone on to the tiny cell, an electrical current was generated.
The proteins come from the chloroplasts of spinach leaves; tiny structures that help plants convert light into energy. As the reaction proceeds, electrons move around and create electrical currents.
But extracting the proteins was not easy. The molecules are delicate and tend to stop working when removed from their natural environment. So the researchers preserved them by mixing them with soap-like molecules called peptide surfactants. The protective molecules appear to form a shield around the energy-producing proteins, fooling them into thinking that they are still part of the plant.

Science News Online gives additional details.

To make the solar cell, a team of biologists and engineers led by Marc Baldo of the Massachusetts Institute of Technology (MIT) harvested photosynthetic proteins from spinach and the bacterium Rhodobacter sphaeroides and deposited the proteins onto a glass support. Because the proteins naturally reside in an aqueous environment inside a cell membrane, it took some creative chemistry to keep the approximately 2 billion isolated proteins functional on a solid surface.
Consider the new material that MIT molecular biologist Shuguang Zhang developed to stabilize the proteins. It consists of synthetic peptides that self-assemble into structures resembling cell membranes. When embedded in the synthetic membranes, the photosynthetic proteins retain their function.
Prototype solar cell from MIT In this prototype solar cell, photosynthetic proteins (spheres embedded in yellow peptides) absorb light and pump electrons (e) into a silver electrode (Credit for legend: Science News Online; credit for image: Marc Baldo).

Science News Online writes that even if these new solar cells are not as efficient today as current photovoltaic devices, they have other advantages.

a protein-based solar cell could be self-repairing, says Baldo. Just as living plants replenish their photosynthetic proteins by swapping out the old copies for new ones, it might become possible to flush a solution of fresh proteins through a solar cell to replace the photosynthetic molecules as they degrade, Baldo explains.

The research work has been published by Nano Letters (Vol. 4, No. 6, Pp. 1079 - 1083, June 2004). If you are a subscriber, you may access the paper, named "Integration of Photosynthetic Protein Molecular Complexes in Solid-State Electronic Devices," by going to this page.

And for more information about Baldo's research, please visit the Laboratory of Organic Optics and Electronics at the Massachusetts Institute of Technology.

Sources: Philip Ball, Nature, June 28, 2004; Alexandra Goho, Science News Online, Week of June 5, 2004; Vol. 165, No. 23 , p. 355; and various websites

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