Using Sweat to Charge Your Cell Phone

Source: Thinkstock

Source: Thinkstock

Imagine using daily exercise not just to power your body, but also your cell phone. That’s what a team of scientists at the University of California-San Diego (UCSD) are working on, with the aid of a temporary tattoo that monitors a person’s progress during exercise and generates power from their sweat.

The tattoo detects lactate, a substance in sweat and “a very important indicator of how you are doing during exercise,” says Wenzhao Jia, a postdoctoral researcher at UCSD involved in the study. A report of her team’s findings was prepared for presentation on August 13 at the 248th National Meeting & Exposition of the American Chemical Society in San Francisco.

Tiring exercise triggers a process called “glycolysis,” which produces energy to maintain the exercise, as well as lactate, which can be detected in your blood. Professional athletes evaluate their fitness and the quality of their training programs by monitoring their lactate levels. Doctors do it for patients with heart or lung disease, both of which cause abnormally high levels of lactate. Current monitoring for athletes is clumsy, though, because blood samples need to be collected and analyzed during exercise — not after.

The UCSD team came up with a faster, easier, and less intrusive way to get this done. They printed a flexible lactate sensor onto paper used to transfer temporary tattoos to skin. The sensor includes an enzyme that removes electrons from lactate, which generates a weak electrical current. The researchers then applied the tattoos to the upper arms of 10 healthy volunteers and measured the electrical current produced during increasingly strenuous exercise on a stationary bicycle over a half-hour. Grasping the significance of their discovery, they built a sweat-powered “biobattery.”

All batteries generate electricity by moving electrons from an anode to a cathode. The UCSD biobattery’s anode contained the lactate-stripping enzyme and the cathode contained a molecule that receives the electrons.

Then the researchers noted something odd in a subsequent test involving 15 volunteers: Those who were less fit — who exercised less than once a week — generated more electric power than those who were moderately fit (exercising one to three times a week.) Exercise enthusiasts who worked out more than three times a week cranked out the least electric power.

So far, the team theorizes that the reason is that people who are less fit tire more quickly, and therefore glycolysis begins sooner during an exercise session. Whatever the reason, though, the most energy these low-fitness volunteers produced was 70 microwatts per square centimeter (0.79-inch) of skin.

“The current produced is not that high,” Jia concedes, but says her team isn’t giving up. “[W]e are working on enhancing it so that eventually we could power some small electronic devices.”

Originally written for OilPrice.com, a website that focuses on news and analysis on topics of alternative energy, geopolitics, and oil and gas. OilPrice.com is written for an educated audience that includes investors, fund managers, resource bankers, traders, and energy market professionals around the world.

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