Micronutrient deficiencies affect millions worldwide, yet checking vitamin C levels still requires blood draws, lab equipment, and high costs that prevent regular monitoring. Most people only get annual snapshots of their health, even though nutrient levels fluctuate much more frequently. Researchers have now demonstrated a simple, noninvasive solution that analyzes vitamin C using the trace sweat naturally produced at the fingertips, offering fast, low-cost, real-time insights without disrupting daily routines.

A team of engineers at the University of California San Diego (San Diego, CA, USA) has developed a flexible sticker that adheres to the outside of a drinking cup and uses a porous hydrogel pad to collect fingertip sweat and incorporates screen-printed electronics embedded in an adhesive polymer sheet. A biofuel cell converts chemicals in the sweat into electricity, powering an onboard circuit and vitamin C sensor, and sending the results wirelessly to a nearby laptop via Bluetooth low energy.

In human tests, the sticker accurately monitored changes in vitamin C after participants drank orange juice or took supplements. The study, published in Biosensors and Bioelectronics, showed that the device could power itself for more than two hours using only sweat-derived energy. Fingertips contain thousands of sweat glands that generate 100–1000 times more sweat than most body regions, enabling continuous energy harvesting even at rest and eliminating the need for batteries.

This effortless monitoring approach offers quicker, cheaper testing than traditional clinical methods and has the potential to improve nutrition tracking in both high- and low-resource settings. Because the sticker can be produced at an extremely low cost, future versions may be disposable and scalable, expanding access to health screening worldwide. The research team plans to adapt the platform to measure additional nutrients, with future iterations expected to send data directly to smartphones or smartwatches for seamless real-time health tracking.

“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 Patrick Mercier, co-senior author of the study. “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.”

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