An e-tattoo on your palm can tell when you're stressed out!

When someone is anxious or excited, their hands often become damp, which can reveal a lot about their mental state. This response is used to assess emotional stress and support those who are struggling with mental health concerns, but the current technology is cumbersome, unreliable, and risks social stigma by placing highly visible sensors on conspicuous body areas.

This sort of monitoring, known as electrodermal activity or EDA sensing, has been applied by researchers at Texas A&M University and The University of Texas at Austin to cutting-edge electronic tattoo (e-tattoo) technology. The researchers developed an e-tattoo based on graphene that links to a smartwatch, clings to the palm, and is essentially undetectable in a new work that was just published in Nature Communications.

"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.

Wearable electronic tattoo technology has been developed for many years by Lu and her partners. Due to its thinness and ability to accurately assess the electrical potential of the human body, graphene has become a popular material.

Such thin materials, however, are unable to withstand much, if any, strain. This makes it difficult to apply them to body regions with a lot of movements, such as the palm and wrist.

How the e-tattoo on the palm can successfully transport data to a rigid circuit--in this example, a commercially accessible smartwatch--in outside-of-lab, ambulatory settings--is the key to this discovery. They employed a serpentine ribbon with two partially overlapping graphene and gold layers.

It can withstand the strain that occurs with movements of the hand for daily activities like holding the steering wheel when driving, opening doors, running, etc. by snaking the ribbon back and forth.

Currently, available palm monitoring technology either applies EDA sensors to other regions of the body, which provides a less precise signal or employs large, conspicuous electrodes that fall off.

Other researchers have attempted to connect a tattoo to a reader using nanometer-thick straight-line ribbons, but they were unable to withstand the stress of continuous movement.

For this study, virtual reality (VR), video games, and the impending metaverse served as inspirations, according to Lu. Although VR is sometimes used to treat mental illness, it still has many shortcomings when it comes to human awareness.

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