An electronic sticker that monitors a user’s vitamin C levels using the sweat from their fingerprints has been developed by a team of engineers at the University of California San Diego.

Requiring no blood draws, lab visits or batteries, the flexible sticker instead adheres to the outside of a drinking cup where it collects trace amounts of sweat as a person grips the cup. In a matter of minutes, the system harvests enough power from the sweat to analyze it for vitamin C and then wirelessly sends the results to a nearby laptop.

Source: David Baillot/University of California San Diego Jacobs School of Engineering

"By turning everyday objects like cups or bottles into smart sensors, people can gain real-time insights into their health and wellness without changing a thing about their daily routine," the team added. "We're moving toward a future of 'unawareables' — devices that are unobtrusive and essentially invisible so that you are unaware that you're even using them. You just go about your day and your drinking cup can give you access to all this rich information."

Because vitamin C plays a significant role in immune function, tissue repair and iron absorption, testing for it requires blood draws and lab equipment and costs, making frequent monitoring impractical for many people, thus prompting the team to devise a solution.

The new sticker was built on a flexible, adhesive polymer sheet and features screen-printed electronic components. Meanwhile, a porous hydrogel pad mounted on the sticker collects sweat from the fingertips and a built-in biofuel cell turns the chemicals present in the sweat into electricity. This powers a custom printed circuit board (PCB) as well as the vitamin C sensor. The PCB reads signals from the vitamin C sensor and then wirelessly transmits that data via Bluetooth low energy.

During trials, the device was adhered to a disposable drinking cup and accurately tracked changes in vitamin C levels after subjects took a supplement or drank orange juice.

In the future, the researchers hope to expand the technology to measure additional nutrients and biochemicals.

An article detailing the team’s work, A smart cup for wireless, biofuel-powered, sweat-based vitamin C sensing,” appears in the journal Biosensors and Bioelectronics.