Quirks & Quarks

A stick-on sensor sucks in sweat and can reveal dehydration and more

The waterproof, wearable sensor can track sweat rate, pH, electrolytes, chloride, lactate, and even glucose

The waterproof, wearable sensor can track sweat rate, pH, electrolytes, chloride, lactate, and even glucose

A Northwestern swimmer wearing an epidermal microfluidic device on the forearm. (John Rogers Research Group)
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This latest advance in wearable technology is a Band-Aid like sweat sensor, the size of a quarter, that's able to get at your body's underlying chemistry to measure things like sweat rate, pH, and other biomarkers such as levels of chloride, lactate, and even glucose.

Dr. John Rogers, a professor in the Department of Materials Science & Engineering and Biomedical Engineering at Northwestern University in Chicago, says there are a lot of reasons we may want a sensor to track our body chemistry.

"That chemistry and chemical signature tells one a lot about physiological health status with relevance all the way from medical science to rehabilitation to sports and fitness, and general wellness," said Rogers. "Sweat, in particular, is an interesting class of biofluid — relatively under-explored compared to blood and interstitial fluid."

The sensor can measure how much a person sweats

"It's a very soft, thin piece of material that has very tiny channels etched into it. So these channels have cross-sectional dimensions similar to those of a human hair, so very fine channels and valves and small reservoirs," said Rogers.

It collects sweat emerging from the skin as a person exercises into the network of microchannels, which is then routed into different reservoirs to allow for precise measurements in real time.

To measure sweat rate or loss, the incoming sweat passes through a food dye. The sweat adopts the colour of the dye, allowing for a visual readout. Since they know the volume of the microchannels, they know how much sweat is lost at any given time based on the intensity of the colour.

"It turns out that that local measurement of sweat rate and sweat loss can be calibrated to full body sweat rate and sweat loss," said Rogers. And that way people wearing these sensors can properly hydrate themselves.

The sensor can also track changes in biomarkers

The sensor can also route the sweat to individual reservoirs where a different colour-changing chemical can indicate levels of other chemical biomarkers.

Rogers said he the sensor can have a "multi-modal array of these reservoirs for sensing the pH level of sweat. We can determine the electrolyte concentration of the sweat. We can determine the glucose level and sweat and the lactate level."

Real world applications

Rogers has a corporate deal with L'Oréal for sensors that can measure pH levels on the skin and with Gatorade "to help athletes understand how to rehydrate and replenish electrolytes."

But what really motivates Rogers are the applications in clinical medicine.

"We can measure creatinine and urea in the context of kidney health. For stroke, we actually measure right-left body asymmetries in sweat rate. It turns out that's a very important metric for tracking the condition of a patient."

He added it could even help to screen infants for cystic fibrosis.

"The clinical standard of care is to measure the chloride level in sweat. So they're already using a sweat diagnostic, but they use very primitive sweat collection techniques," said Rogers. "These soft pads and microfluidic devices are just a much more appealing way to collect the sweat, store it, and do onboard analysis."

They currently have active programs in all three of those clinical areas with initial pilot studies on human subjects.

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