In 2013, on a visit to a Ugandan clinic, Manu Prakash noticed a small metal machine propping open a door. It was a centrifuge—a device that spins tubes of liquid at extremely high speeds, so that any particles within them sink to the bottom. This process is used to separate out everything from cells to viruses to DNA, which means that centrifuges underpin a lot of modern science. They’re as essential to hospitals and laboratories as saucepans are to kitchens.
But centrifuges run on electricity, which is why many clinics in the developing world can’t use them, even if they can afford them. That’s why the one that Prakash visited had repurposed their centrifuge as a doorstop. It’s also why the clinic couldn’t carry out a lot of simple diagnostic tests. “On a chart, they listed all the tests that they do, but they were only really doing two out of 10,” recalls Prakash. “The other eight required centrifugation. I’ve seen this play out over and over again. It was clear that we needed a centrifuge that could operate without electric power.”
Prakash has now created one. Modeled on an ancient children’s toy, and made with little more than paper, string, and tape, it can spin at speeds of up to 125,000 revolutions per minute (rpm). That’s more than enough to, say, separate cells or malaria parasites from blood samples. And it’s actually much faster than a lot of desktop centrifuges, even though Prakash’s device is entirely hand-powered, weighs less than 2 grams, and can be made for just 20 cents. He calls it the paperfuge.