A new electric generator has a modest and unexpected energy source: A small strip of latex rubber coated with bacterial spores.
The contraption makes use of the harmless soil bacterium Bacillus subtilis, which has a neat survival trick. When nutrients are scarce, it turns itself into a tough little spore that can withstand heat, desiccation, chemical assaults, radiation, and anything else the world can throw at it. These spores respond to changes in humidity. When the air dries they shrivel up like grapes turning into raisins; when the air is moist they plump up again. Researchers from Harvard's Wyss Institute and several other universities realized they could harness that physical movement, and could make an actuator to generate electricity.
In the experiment, published this week in Nature Nanotechnology, the researchers slathered one side of a sheet of rubber with the bacterial spores. When the sheet dried it curled up, much like a leaf does after it falls from a tree. Increasing the humidity caused the sheet to straighten out again. Researcher Ozgur Sahin then built a humidity driven generator out of Legos, in which the spore-coated rubber acts as a cantilever that flips back and forth, driving a rotating magnet to produce electricity.
Such a device, properly scaled up, could use the natural evaporation of water to generate useful amounts of clean electricity, the researchers say.
Images and video: Xi Chen/Columbia University