Tattoos have been around for as long as our society has existed, whether for aesthetic or spiritual reasons. But now, researchers are increasingly looking at another type of tattoo: medical tattoos. The idea behind them is simple: you have an electronic tattoo (e-tattoo) that doubles as a health sensor and can tell you various aspects of your health.

An e-tattoo basically functions as an unobtrusive sensor. They’ve been used for various purposes, from monitoring blood pressure to various health conditions. In this case, researchers at The University of Texas at Austin and Texas A&M University applied them to people’s palms, to monitor emotional stress and help people get an edge against mental health issues.

You don’t necessarily need to have sweaty palms when you’re nervous — but your palms do actually say a lot about your mental state, and the e-tattoo can pick it up. Palm sweating commonly happens as a response to fear or stress, and is considered to be a relatively common symptom associated with anxiety.

Here, researchers coupled e-tattoo technology with electrodermal activity (EDA) sensing. EDA devices have been used before, but they’re usually bulky and cause obvious discomfort (few people would be content walking with electrodes on their body on a day-to-day basis). The e-tattoo can tell when people get excited or nervous while being barely visible.

“It’s so unobstructive that people sometimes forget they had them on, and it also reduces the social stigma of wearing these devices in such prominent places on the body,” said Nanshu Lu, professor in the Department of Aerospace Engineering and Engineering Mechanics and leader of the project.

Lu and colleagues have been working on e-tattoo for years now, and they know that the key to making a good one is to make it thin enough to be unobtrusive, while also having the electrical properties that enable it to measure physiological parameters. The challenge of robust electrical connection between the ultrathin circuit and the palm has previously been a barrier to clinical use.

To overcome this, the authors used a combination of materials that includes graphene.

Graphene is a great material for this purpose: it’s a two-dimensional material with excellent electric properties, but it’s extremely thin (that’s why it’s considered two-dimensional) — and because it’s so thin, it’s not very resilient.

To make the approach more durable, researchers used a serpentine ribbon that has two graphene layers and gold partially overlapped. This design makes it much more durable against the day-to-day movement of palm activity, and the data is transferred to a commercially available smartwatch. Several alternative designs were trialed, but this one proved to be by far the most resilient.

The key application would be to enable people to be more aware and in control of the state of their mental health. For instance, you could gain constant insights into whether (and how) a particular treatment is working.

“You want to know whether people are responding to this treatment,” Lu said. “Is it helping them? Right now, that’s hard to tell.”

But the more general potential of e-tattoos extends far beyond just this. Researchers believe e-tattoos could be an instrumental development for personalized medicine. Unlike today’s medicine, which largely offers a one-size-fits-all approach, personalized medicine is an approach that takes into account an individual’s unique genetic, environmental, and lifestyle factors, to tailor medical treatment and prevention strategies. But in order, you need a lot of personalized information — and that information could come from e-tattoos, if they can be robust and unobtrusive enough.

Hongwoo Jang et al, Graphene e-tattoos for unobstructive ambulatory electrodermal activity sensing on the palm enabled by heterogeneous serpentine ribbons, Nature Communications (2022). DOI: 10.1038/s41467-022-34406-2