New Wearable Medical Sensors Run on Fingertip Sweat

The slim, flexible device could measure blood glucose or heart rate without the need for batteries

fingertip sensor
This wearable sensor harvests sweat from the fingertips to generate the electricity it needs to measure things such as heart rate and blood-sugar. UC San Diego

A newly developed medical sensor runs on fingertip sweat, reports Rachel Fritts for Science. The researchers behind this perspiration-powered device were able to make it thin and flexible like a Band-Aid by ditching the need for bulky batteries that weigh down other medical sensors. Even without batteries, the slim new sensors could be used to detect measures of health and nutrition such as blood-glucose levels, heart rate or vitamin deficiencies.

New Scientist's Matthew Sparkes reports that the new sensors, described in a paper published this week in the journal Joule, soak up a compound present in human sweat called lactate with a patch of foam that contains an enzyme that oxidizes the lactate to generate electricity.

A typical 10-hour night of sleep can yield 20 to 40 microwatts of power per finger pad, which, as New Scientist notes, wouldn’t charge a smartphone but could keep a wrist watch going for 24 hours—and it's more than enough juice to keep the sensors online. Researchers say they chose the fingertips as the location for their device because the fingertips actually boast the highest concentration of sweat glands on the human body—each one has more than 1,000 that are basically always sweating regardless of what we’re doing.

This device isn’t the first medical sensor to run on sweat, according to Science, but it is the first one that doesn’t require a torrent of perspiration to harvest enough lactate to survive.

“Unlike other sweat-powered wearables, this one requires no exercise, no physical input from the wearer in order to be useful,” says Lu Yin, an engineer at the University of California, San Diego and lead author of the research, in a statement. “This work is a step forward to making wearables more practical, convenient and accessible for the everyday person.”

Fingertip-powered wearable

Though the sensors can subsist on sweat alone, they can also harvest energy from light pressure being applied through the fingertips in activities such as typing, texting or even tapping out a tune on a piano.

“Our goal is to make this a practical device,” Yin says in the statement. “We want to show that this is not just another cool thing that can generate a small amount of energy and then that’s it—we can actually use the energy to power useful electronics such as sensors and displays.”

Yin tells New Scientist the enzyme being used in current prototypes of the device only last about two weeks before they lose their ability to generate electricity. The next step will be to develop a more stable enzyme that could extend the sensor’s lifespan.

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