Sweat is a smelly side effect of wearing a fitness tracker. When you finish your workout, you probably grab a wet cloth to wipe down your wearable. But what if the whole point was to get your tracker sweaty?
Researchers at North Carolina State University have developed a prototype for a new kind of wearable that actually relies on your sweat. Using a replaceable test strip embedded with chemical sensors, the device can measure the amounts of certain metabolites present in your sweat to give a sense of your overall health.
The applications for such a wearable range from detecting dehydration, to athletic recovery, to even military or competitive sports training, the researchers say in their new study, published in Biosensors and Bioelectronics.
“This technology allows us to test for a wide range of metabolites in almost real time,” Michael Daniele, an assistant professor of electrical and computer engineering at NC State, said in a press statement.
Still, experts in sweat analysis and sweat forensics tell Popular Mechanics that measuring for multiple metabolites on one tiny device can get pretty complicated.
In this study, which is solely a proof-of-concept, the researchers focused on measuring four metabolites that could tell them about a person’s glucose, lactate, pH, and temperature levels just through sweat analysis.
Metabolites are small molecules your body forms in the process of metabolism, so these biomarkers can tell you about your health by measuring those metabolite levels against your normal parameters. That way, doctors will know if your lactate levels are high, for instance, which could indicate very real health problems like heart failure, sepsis, or even liver disease, as your liver breaks down lactic acid.
To measure various metabolite levels, there is a replaceable strip on the back of the device that uses chemical sensors to come into contact with your sweat. Then, data from the strip’s sensors are interpreted by hardware inside the tiny device and results are routed back to a smartphone, smartwatch, or other device—just as a Fitbit uses an accelerometer to figure out how fast you were running, reporting that back to your phone.
“We’re optimistic that this hardware could enable new technologies to reduce casualties during military or athletic training, by spotting health problems before they become critical,” Daniele said. “It could also improve training by allowing users to track their performance over time. For example, what combination of diet and other variables improves a user’s ability to perform?”
From a design standpoint, the scientists had to cram a bunch of analytical equipment, like electrodes, into the device.
“[It] is the size of an average watch, but contains analytical equipment equivalent to four of the bulky electrochemistry devices currently used to measure metabolite levels in the lab,” Daniele said. “We’ve made something that is truly portable, so that it can be used in the field.”
There’s no doubt the engineering of the device is impressive, Jan Halámek, an assistant professor of chemistry at the University at Albany, tells Popular Mechanics. (Halámek wasn’t involved in the study.) Bringing electronics and sweat analysis tools down to this size is a novel concept and quite clever.
But Halámek says applying electrochemistry to the body “is not easy at all.” That’s backed up by recent developments like temporary tattoos to measure lactate levels and prior work to measure glucose levels in sweat.
Attempting to measure multiple metabolites on a small device is even trickier, Halámek says, because some of the metabolites the researchers are measuring actually break down into similar groups of compounds. For instance, both lactate and glucose break down to peroxide. Since the electrodes to measure each are close together, there’s a risk that measurements will be off; Halámek says it’s particularly easy for the peroxide made from lactic acid to overcome that of glucose.
When the researchers move onto other types of metabolites for their device, calibration will also be tricky. Some metabolites are particular to certain people, and they exhibit them in various concentrations depending on their weight and biochemistry, Halámek says.
Other measurements, like for glucose, won’t really tell you much about your health other than the binary “good health/bad health” result you could expect from testing for glucose. Above a certain point, high glucose indicates diabetes, but what if you’re already diabetic? Looking for these metabolites wouldn’t be helpful unless you could instantly find out if your glucose levels are too high and you need insulin, stat—but those kinds of devices already exist.
And, strangely enough, contaminants on your skin could even impact results, Halámek says.
“Imagine you get a donut at the gas station, then on those dirty hands you measure glucose and you get a really high number,” he says. “It’s not accurate.”
Overall, Halámek is careful emphasize the research is sound and believes the design is promising, but he says the electrochemistry will require further research. “It will be very tough,” he explains. “The practicality is questionable.”