Sweat sensor sticker monitors vitamin C in real time

A team of engineers at the University of California San Diego has developed an electronic sticker that can monitor a person’s vitamin C levels using the sweat from their fingertips — no blood draws, lab visits or batteries required.

The flexible sticker, which attaches to the outside of a drinking cup, collects trace amounts of sweat as a person grips the cup. Within minutes, the system harvests enough power from the sweat to analyse it for vitamin C and wirelessly sends the results to a nearby laptop.

The research findings have been published in Biosensors and Bioelectronics.

“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,” said study co-senior author Patrick Mercier, a professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering. “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.”

The sticker consists of a biofuel cell (black arches) beneath a porous hydrogel pad that collects fingertip sweat, printed circuit board, and vitamin C sensor (small black circles connected to the printed circuit board). Image credit: UC San Diego Jacobs School of Engineering.

Malnutrition and micronutrient deficiencies continue to affect millions of people worldwide. While vitamin C plays a key role in immune function, tissue repair and iron absorption, testing for it currently requires blood draws and specialised laboratory equipment. These barriers make frequent monitoring impractical for many people.

The new sticker offers a simple and convenient alternative. Built on a flexible, adhesive polymer sheet, the system integrates screen-printed electronic components. A porous hydrogel pad mounted on the sticker collects sweat from the fingertips. A built-in biofuel cell converts chemicals in the sweat into electricity, which powers a custom printed circuit board and the vitamin C sensor. The circuit board reads signals from the vitamin C sensor and wirelessly transmits the data via Bluetooth low energy.

Study co-first author Muhammad Inam Khan demonstrates fingertip placement on the sticker while gripping a boba drink. Three fingertips rest on the arched biofuel cell (left) while the tip of the middle finger rests on the vitamin C sensor (right). Image credit: UC San Diego Jacobs School of Engineering.

“Most people only get a snapshot of their health once a year at the doctor. But our bodies change much more frequently than that. We want to make access to health data as frequent and effortless as holding your morning coffee cup or orange juice bottle,” Mercier said.

Another special feature of the sticker is that it generates power without requiring physical exertion from the user. Fingertips, despite their small size, are among the body’s most prolific sweat producers — each is packed with over a thousand sweat glands and can produce between 100 to 1000 times more sweat than most other areas on the body. This steady trickle of natural perspiration provides a continuous energy source that allows the sticker to operate even when the user is at rest.

Because the system is battery-free, it can be manufactured at low cost — potentially for just a few cents per unit. Its affordability could also make future versions of the system disposable and widely accessible, particularly in low-resource areas.

The work is a collaboration between the labs of Mercier and Joseph Wang, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering.

In tests, the device was stuck onto a disposable drinking cup and accurately tracked changes in vitamin C levels after participants took a supplement or drank orange juice. The device powered itself for more than two hours using only sweat-derived energy.

“This is an elegant extension of our early fingertip sweat-based technology toward effortless, continuous monitoring of personal nutrition and health. By moving sensors from the skin to the surface of everyday objects like cups or bottles, we are expanding what wearable technology can be,” Wang said.

Study co-first author Ryan Burns uses the sticker on a cup filled with orange juice. Image credit: UC San Diego Jacobs School of Engineering.

The team plans to expand the technology to measure additional nutrients and biochemicals. Future versions could send readings directly to smartphones or smartwatches to provide more seamless, real-time tracking of personal health data throughout the day.

Top image caption: This battery-free electronic sticker attaches to everyday objects like a drinking cup and monitors vitamin C levels from a person’s fingertip sweat. Image credit: David Baillot/UC San Diego Jacobs School of Engineering.