Bacteriophages a few nanometers in size live up to the ambiguity of the word "battery": They stand in rank and file like soldiers and generate voltage.
Viruses are usually frightening pathogens: they invade cells in order to use them to multiply, often triggering serious diseases or epidemics. Influenza, measles or rubella are just as much a part of this as smallpox, rabies or the immune deficiency AIDS. Their strength is their extremely high resilience, because they withstand the toughest environmental influences. Their ability to adapt relatively quickly helps them, often accompanied by the spontaneous mutation of their genetic material.
What regularly causes headaches for medical professionals and hygienists is now seen as a welcome playing field by some nanoengineers. Some of them are already experimenting with such DNA structures. They vaporized the genetic material with metal in order to produce nanometer-thin wires that are supposed to supply nanoscopically small machines with energy. What they were still missing was a power supply of this size that was as powerful as possible – preferably a rechargeable battery.
Now there's pioneering work by an American-Korean team from the Massachusetts Institute of Technology in Cambridge, Massachusetts. The working group helped nature a little. She bred bacteria-infecting viruses - called bacteriophages - called M13. They are particularly good at binding cob alt oxide molecules and gold atoms into the protein coat that surrounds the germs. "We focused on cob alt oxide because it has a very high electrical capacitance," says project leader Angela Belcher of MIT. In this way, she and her team create tiny, natural wires. They are six millionths of a millimeter thick and 880 long - as big as the virus. If you place a pile of them on a polymer surface, these bacteria killers align themselves as if on command – much like a company of soldiers standing to attention. "At the same time, we can make millions of clones of them with relative ease," claims Belcher.
Now the important thing is that the army of viruses on the polymer behave as if they were electrically negatively charged. In contact with an electrolyte, they allow current to flow. That is the essence of a battery. "With our arrangement, we achieve energy densities that are two to three times higher than those of conventional batteries," says Belcher. What's more, the structure shows excellent behavior during recharging. The added gold further improves the electrical properties. The experimenters subjected their miniature accumulators to more than twenty charging cycles, and they achieved values of 600 milliampere hours per gram at a voltage of up to three volts.
The researchers now believe they can use it to create compact energy sources that are as small as grains of rice. They could be used in hearing aids, for example. In addition, the experimenters show that extraordinarily flexible layers can be produced. Another advantage the scientists describe is the fact that they can multiply their electric viruses at normal room temperature and normal atmospheric pressure, which makes the manufacturing process cheap.
Therefore, the researchers expect that their electrifying viruses will not only be good for expensive niche products. You are also thinking, for example, of batteries for cars – after all, several attempts to introduce electric vehicles have failed because the power storage devices used did not perform well enough. The working group believes that this could soon change with a bacteriophage battery.