Piezoelectric materials build up charge when pushed or squeezed. These materials may be familiar to you: they generate the spark in a gas lighter, and motors powered by such materials vibrate some cell phones. Piezoelectric materials made of metals or polymers require large inputs of energy to build up a charge. Bone, DNA, and protein fibers are weakly piezoelectric, but it’s hard to efficiently organize these materials on a large scale to yield electricity.
To handle this organizational issue, Seung-Wuk Lee, of the University of California in Berkeley and the Lawrence Berkeley National Laboratory, and his colleagues looked for a biomaterial that had intrinsic order and was easy to make. They settled on the M13 bacteriophage, a rod-shaped virus that only infects bacteria. One bacterium can produce one million copies of the virus within four hours, so starting material isn't a problem. And the virus neatly arranges itself in stacked rows when spread on a surface.
The researchers first tested the virus to see if it was piezoelectric. Instead of pushing on the virus and measuring a current, they looked for the opposite effect. They electrified a film made with the virus and watched for mechanical motion. The scientists saw the helical proteins covering the virus twist.
