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Between Age, a dark adage sometimes has come in European folklore and children’s stories: Woe to this child who, kissed on the forehead, tastes salty. He is bewitched and must die soon. A salty-headed newborn was the dreadful sign of a mysterious disease. The diagnosis of witchcraft didn’t hold up, of course, but today researchers believe the salty taste warned of the genetic disease we know today as cystic fibrosis.
Cystic fibrosis affects more 30,000 people in the United States and over 70,000 worldwide. Mutations in the CFTR gene scramble cells’ blueprints for making protein tunnels for chloride ions. The negative charge of chloride attracts water, so without a lot of chloride snaking through cells, the body’s mucus becomes thicker and stickier, making it difficult to breathe and often trap dangerous bacteria in the lungs. It also prevents digestive enzymes from leaving the pancreas and entering the intestine, causing inflammation and malnutrition.
Salty sweat is a telltale sign. Doctors sometimes meet children 10 times higher than expected chloride levels in their sweat. Since the 1960s, measuring chloride has given doctors their clearest diagnoses: They stimulate people’s sweat glands, absorb as much as possible, and send the samples to labs. But the tools are expensive, bulky, and difficult to fit on squirming babies. Sometimes the tests do not collect enough fluid for a diagnosis. And if a test fails, parents and their newborns often have to wait a few weeks to return.
“Not collecting enough sweat only delays the diagnosis,” says Tyler Ray, a mechanical engineer at the University of Hawaii at Mānoa, who develops portable biosensors. It means wasting precious weeks when doctors could have prescribed treatments. It also creates a barrier for people who have to drive for hours – or fly over oceans – to get to a hospital that can perform the test. “There aren’t many in the whole country,” says Ray. “In fact, Hawaii doesn’t have one for the general population.”
Ray’s team of engineers and pathologists think they have an alternative: sticky sweat traps. In a study published last week in Scientific translational medicine, they report creating a malleable, coin-sized sticker that changes color as it absorbs higher and higher salt concentrations indicating cystic fibrosis. When tested on babies and adults, the stickers fill more sweat than traditional devices, and do so faster.
“This is exciting technology and something very new,” said Edward Fong, a pediatric pulmonologist at Hawaii Pacific Health who was not in the study. Fong believes these stickers would make the diagnosis of cystic fibrosis more accessible. If it gets regulatory approval, he says, “we don’t need to send our patients 2,500 kilometers to be able to get their sweat tested.”
“Making sweat testing easier would be the only obvious victory,” admits Gordon Dexter, a 36-year-old man from Maryland who lives with the disease. Dexter is a moderator of the Reddit community r / Cystic fibrosis, where people sympathize with digestive difficulties and celebrate triumphs on lung bacteria. “Sweat tests can be a bit ambiguous or just hard to do, and it’s a common question I’ve seen,” Dexter says.
Ray has had an eye on sweat for years. In 2016, as a postdoctoral fellow, he joined John Rogers Laboratory at Northwestern University, where researchers had played with performing sweat analyzes on wearable sensors. They wanted to create new devices with tiny channels, valves, and dyes that could track body chemistry in real time. Shortly after Ray arrived, the laboratory published an article demonstrating a wearable sensor that could reveal the levels of glucose, lactate and chloride ions in sweat, as well as its pH. This study presented the sensors as monitors for athletes or military personnel in training, and the researchers tested it during a long-distance bike race. The technology got a lot of attention: Ray went on to work with sports teams like the Chicago Cubs, and Gatorade has used technology sell his Gx sweat patch. In 2017, the patches were exhibited at New York’s modern Art Museum and have been used to promote hydration in South by southwest Festival.
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