Scientists are working on e-tattoos that monitor your sweat

Graphene e-tattoos are wearable biosensors that stick directly to the skin
Researchers are now developing patches that can read compounds in sweat
These could indicate a range of conditions, as well as detecting stress

Invisible sweat sensors could one day be used to detect health conditions. That’s according to ongoing research at the University of Massachusetts Amherst, where a lab is developing stick-on graphene tattoos that can read and report on what’s in your sweat.

We’ve heard before that wearable sensors have the potential to revolutionize health monitoring. First developed by a team at Northwestern University, these electronic skin patches are made using graphene. Less than a millimeter thick, they’re practically invisible and can flex with the skin. In years to come, the idea is that we could be wearing these patches for real-time readings around the clock.

So far, the main focus for scientists has been how to use these biosensors to measure heart rate and blood pressure – both key markers of potential health complications. However, the next generation of these patches could get data from a different bodily source: sweat.

Sweating the small stuff

In 2017, researchers at the University of Texas created an even thinner version of a graphene biosensor. One that was applied to the skin by wetting a sheet of transfer paper – just like a temporary tattoo. Using e-tattoos like this, scientists at the University of Massachusetts Amherst are now attempting to harness the secrets of sweat.

According to Dmitry Kireev, a member of that team, sweat carries certain compounds out of the body and onto the skin. The team’s first focus is cortisol, an indicator of stress, stroke risk, and a number of other disorders.

Monitoring sweat isn’t a new pursuit. Several labs are working on stick-on patches that do precisely that. Some change color when certain chemicals are present, while others are attached to large electrochemical sensors. Both require chambers to collect sweat. What makes graphene e-tattoos so exciting is that they don’t – making them much smaller.

In simple terms, the graphene itself is used as a transistor. When a certain substance in sweat meets molecules on the graphene’s surface, an electrical signal is produced. Through changes in the transistor’s resistance, the amount of that substance is reported.

Down the line, the hope is that these graphene e-tattoos can be used to detect other compounds in sweat, including glucose, lactate, and estrogen. These could, in theory, be used to indicate potential health issues.

Worn as a lifestyle accessory, e-tattoos could act as early indicators of certain conditions or simply as a source of additional data to feed into the best fitness apps. In a medical scenario, the biosensors could provide real-time data without the need for blood tests.

It’s all clever stuff, but the wearable future is still a way off. For now, graphene e-tattoos still need to be wired up to an electronic circuit with a computer chip – albeit a tiny one – to transmit data from sweat. That means they’re not yet the flexible, invisible future of healthcare.

To reach that stage, researchers will need to create fully integrated circuits using graphene, including power sources and wireless transmitters. That process will probably require some blood and tears, in addition to sweat. Still, in the next decade, Kireev predicts we’ll see sweat-sensing e-tattoos built into the best smartwatches.