Instead, those bacteria pass through several layers of cotton, where an electrical field zaps them with 20 volts of electricity for several seconds. It's a technique that researchers have dubbed conductive "nano-coated" cotton. Twenty volts is barely enough to make a human tingle, but tests found that more than 98 percent of Escherichia coli bacteria were killed instantly.

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Cui and the team created this nanofilter by dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes. They used cotton because you can find it anywhere in the world, and they used a "negligible" amount of silver, all in an effort to keep costs low.