One day, not too far into the future, your sweat from a morning run may charge-up your smart phone—or other electrical devices. A team at the University of California, led by Joseph Wang, Distinguished Professor and Chair of Nanoengineering, has produced “the first examples of epidermal electrochemical biosensing and biofuel cells that could potentially be used for a wide range of future applications.”
Catherine Paddock, writing for Medical News Today, explains how it works. As we exercise we sweat and sweat contains lactate. The harder we exercise the more lactate we produce . At some point anaerobic respiration kicks in and converts glucose to lactic acid, generating energy in the process, according to Wenzhao Jia, a postdoctoral student in Wang’s lab.
Jia and her colleagues have developed a sensor to measure lactate in real time. The sensor can be imprinted onto a temporary tattoo and works by stripping electrons from lactate molecules—thus producing a weak electrical current. Paddock reports that the scientists tested the new device on ten volunteers, applying the tattoos to their upper arms and measuring how much electrical current they produced as they exercised.
Ten volunteers pumped their stationary bikes for 30 minutes while scientists tested the sensors’ ability to monitor sweat lactate levels. Then it was on to the big test—to see if they could make a sweat powered battery. Paddock explains, ”They used the enzyme that strips the lactate of electrons to act as the anode, and used a chemical that accepts the electrons to be the cathode. Electrons moving from an anode to a cathode is the basic principle on which a battery works.”
This time 15 volunteers, with the temporary tattoo applied to their upper arms, pedaled the stationary bikes. Oddly, the less fit volunteers produced the most power. “Those who exercised only once a week produced more power than those who exercised at least three times a week. One possible explanation is that less fit people become fatigued more quickly, causing lactate-producing anaerobic respiration to kick in earlier”, Paddock wrote.
The less fit bikers produced about 70 uW per square centimeter of skin. Jia says that that is not a large amount of current. She is working on how to enhance it so it could eventually provide enough power to run small electrical devices. The National Science Foundation and the Office of Naval Research are funding the work.
