The small beads of sweat your fingertips produce while you sleep could power wearable sensors that measure glucose, vitamin C, or other health indicators. That’s the promise of a new advance, a thin, flexible device that wraps around fingertips like a Band-Aid, that its creators say is the most efficient sweat-powered energy harvester yet. Sweat is a particularly promising energy source because it contains a natural byproduct of anaerobic respiration (the method used by your body to get energy quickly when you exert yourself) called lactate that can be broken down by an enzyme to produce energy. However, existing devices need a lot of sweat to work, and most people don’t want to hit the gym whenever their electronics run out of power.
The new device is just 1 square centimeter wide and flexible enough to wrap around a fingertip. It captures sweat with a flexible hydrogel that sits against the skin. Three foam blocks on top of the gel serve as electrodes. Two contain an enzyme that takes electrons from lactate and the other contains platinum that uses those electrons to convert oxygen into water. This process creates a flow of electrons through the device that generates electricity. The device can generate 300 millijoules of energy per square centimeter during a night’s sleep, enough to power a wristwatch for a day. What’s more, if a person wearing the device applies pressure by pinching two fingers together, it can produce 30 millijoules per square centimeter thanks to generators that turn the mechanical energy into electricity.
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