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The tattoo biosensor (enlarged to show detail) (Joseph Wang)

Using Sweat To Power Devices Isn’t Far Off

An intense workout at the gym could one day not only recharge your batteries, but your phone's too

smithsonian.com

Working up a sweat is good for your body. But in the future, it could recharge not only your energy levels but those of your electronics. In research presented at the American Chemical Society, researchers showed the potential for using small temporary tattoos as batteries, charged by the lactic acid found in sweat.

The tattoo was initially developed as a diagnostic tool for detecting lactate, which is usually present in sweat after intense periods of exercise. Sometimes it also shows up if a person has certain kinds of heart or lung disease. Because of this, both professional athletes and patients with potentially serious conditions have their lactate measured by doctors. Currently, lactate levels are measured with blood draws, taken while the subject is exercising. But getting jabbed with a needle during a sweat session is nobody’s idea of a good time. 

Enter the temporary tattoo. The tattoo has a tiny sensor built in that measures the lactate level during exercise—no need for needles. The biosensor is made from an enzyme that reacts with the lactate, creating a small electrical current. The researchers also added a battery that could store the energy produced.      

"The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices," researcher Wenzhao Jia said in a press release. "Right now, we can get a maximum of 70 microWatts per cm2, but our electrodes are only 2 by 3 millimeters in size and generate about 4 microWatts — a bit small to generate enough power to run a watch, for example, which requires at least 10 microWatts. So besides working to get higher power, we also need to leverage electronics to store the generated current and make it sufficient for these requirements."

The Washington Post reports that the tattoos, though only able to hold a small charge right now, can be produced for just a few cents and could be used for 10-12 hours. And the tattoos are just the start. The resaerchers hope that one day, their sensors could be placed in fabrics and clothing, including underwear.

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