Researchers in Austin, Texas, are taking aim at an old but crucial tool for studying the human brain: the electroencephalogram, or EEG. For nearly a century, EEGs have helped scientists and doctors measure the electric pulses that fire through our brains, diagnosing everything from epilepsy to traumatic brain injuries. But they’ve always come with strings attached — literally.

Now, a team of scientists has introduced a stunning upgrade. They’ve created a liquid ink that can be sprayed directly onto a person’s scalp, forming an ultra-thin electronic tattoo. This “tattoo” EEG listens to the brain beneath it.

“Our innovations in sensor design, biocompatible ink, and high-speed printing pave the way for future on-body manufacturing of electronic tattoo sensors,” says Nanshu Lu, one of the lead researchers at the University of Texas at Austin. “It has broad applications both within and beyond clinical settings.”

The invention, detailed in the journal Cell Biomaterials, is being heralded as a potential game-changer, not just for brain monitoring but for the growing field of brain-computer interfaces—the futuristic devices that let people control machines with their thoughts.

From Wires and Gels to a Simple Spray

For anyone who’s endured an EEG, the process feels beyond cumbersome. A technician marks a dozen or more points on your scalp, applies sticky gel, and painstakingly glues electrodes to your head. These electrodes connect to a machine via a tangle of wires. The setup is clunky, uncomfortable, and prone to failure as the gel dries out.

Lu and her collaborators wanted something better. They’ve spent years designing tiny sensors, known as electronic tattoos or e-tattoos, which stick to the skin to measure everything from heartbeats to muscle fatigue. But applying these tattoos to the scalp posed a challenge.

“Designing materials that are compatible with hairy skin has been a persistent challenge in e-tattoo technology,” Lu explains.

Then, their breakthrough came in the form of a new kind of liquid ink made from conductive polymers. The ink flows effortlessly through hair to reach the scalp, where it dries into a thin, flexible film. Once in place, the tattoo acts as a sensor, picking up brain signals with precision.

The process is remarkably simple. Researchers map out the electrode locations using a computer and then use a specialized inkjet printer to spray the liquid ink onto the scalp. Within minutes, the ink dries, forming a lightweight, unobtrusive tattoo. No discomfort; no glue; no wires.

A More Reliable Brain Listener

To test their invention, the researchers applied these temporary tattoos to the scalps of five volunteers with short hair. For comparison, they also attached traditional EEG electrodes next to the tattoos. The results were telling.

After six hours, the gel on the conventional electrodes began to dry out. A third of them stopped working entirely, and the remaining electrodes delivered weaker, noisier signals. The e-tattoos, in contrast, performed flawlessly for at least 24 hours.

The researchers didn’t stop there. They redesigned the tattoos to replace the wires typically used in EEG setups. By tweaking the ink’s formula, they printed thin lines connecting the sensors to a small data collection device. These printed “wires” conducted signals reliably without picking up interference.

The team envisions a future where even these short wires are unnecessary. “This tweak allowed the printed wires to conduct signals without picking up new signals along the way,” says Ximin He, a co-author from the University of California, Los Angeles. Their next step is to embed wireless transmitters directly into the tattoos.

Brain-Machine Interfaces, Redefined

Beyond making EEG tests more comfortable and accurate, the researchers see their technology playing a role in the rapidly evolving field of brain-computer interfaces. These devices, which translate brain signals into commands for external systems, hold immense promise for people with disabilities, offering the ability to control prosthetic limbs or communicate without speaking.

Right now, brain-computer interfaces are bulky and unwieldy. Users typically wear large headsets bristling with electrodes. José Millán, another co-author from the University of Texas at Austin, believes e-tattoos could change that.

“Our study can potentially revolutionize the way non-invasive brain-computer interface devices are designed,” he says. By printing sensors directly onto the scalp, e-tattoos could eliminate the need for headsets altogether, making these devices more accessible and easier to use.

A Glimpse of What’s Next

The idea of wearing electronics on your skin might seem futuristic, but it’s becoming a reality. In recent years, e-tattoos have made their way onto athletes’ chests, tracking heart rhythms, and onto people’s arms, monitoring muscle fatigue. Now, they’re climbing the ladder—straight to the brain.

For now, the liquid ink is confined to the lab, but its creators see a world of possibilities ahead.

“E-tattoos represent a new frontier in wearable technology,” says Lu. “This is just the beginning of what we can achieve.”