Plants are the world’s best solar cells, effortlessly converting sunlight into the energy needed for growth. In June biochemist Shuguang Zhang and his colleagues at MIT showed they could bend that capability to a technological end, using light-harnessing proteins from spinach to convert sunlight into an electrical current.
The set of spinach proteins, known as Photosystem I, is a well-known component of the photosynthetic process. Until now, however, nobody had been able to figure out how to make them work in combination with electronic circuitry because the proteins cannot survive without water and salt—ingredients that do not mix well with electronics. Zhang solved the incompatibility by creating “detergent peptides,” molecules that form protective shells around the photosynthetic proteins. The peptides seem to hold water inside their shells and prevent it from leaking out. “They keep Photosystem I wet and stable but keep the water away from attached electronics,” Zhang says.
His team placed a piece of glass and an electrically conductive material on top of the spinach-peptide mixture and a semiconductor and an electrode below it. When the researchers shone a laser on this spinach sandwich, the photosynthetic proteins harvested electrons freed by the laser’s photons. Instead of creating a sugar molecule, as they would in a spinach leaf, the electrons passed through the semiconductor and into the electrode.
Although the electric current from the spinach sandwich was feeble, Zhang says that many layers of light-capturing proteins could extract more power. Eventually, plant-based solar cells might be built into the case of a laptop computer or cell phone to extend battery life. “After a few hours on a cellular phone, you’re out of power. With this, you just need light,” Zhang says. “But you still need batteries—sometimes you have to call in the dark.”