Brain science can be messy, even when no one’s skull is getting opened up. The common non-invasive technique of electroencephalography (EEG) reads electrical activity of the brain through the scalp. Many EEG setups involve conductive gel and a tangle of electrodes and wires that contribute to noisy data, producing so-called motion artifacts when the person moves their head.
Now, a researcher team from the Georgia Institute of Technology and several universities in Korea have debuted a clean solution: A small electrode, less than one millimeter wide, which can be pressed into the scalp between hair follicles. The device is held in place by five tiny conductive spikes, or microneedles, which are just long enough to penetrate the outermost layer of skin, which is mostly oils and dead skin cells. The researchers described their device and some demonstrations of its performance in a paper published this week in the Proceedings of the National Academy of Sciences.
The small size and mass has an added benefit of producing fewer motion artifacts. The electrode wiring can connect to a small wireless transmitter, further reducing bulk and potential complications from additional wiring. Researchers demonstrated the sensor as part of a brain-computer interface (BCI): Users controlled a video call on an augmented reality headset while walking or jogging on a treadmill and going up and down stairs. In testing, the device performed well 12 hours after being applied to the scalp, far longer than the traditional devices it was compared against.
Applications for the New Electrode
“It’s an exciting first step,” says Jane Huggins, an engineer at the University of Michigan who was not involved in the new research. She studies BCIs for people with physical impairments such as cerebral palsy, which may cause uncontrolled movement. The new electrodes might one day be a good option for a communication device for those patients, says Huggins, if they respond well to practical issues, such as different hair types, sweat, headrests, and electrical noise from other devices.
The sensor developers emphasize the technology’s potential versatility, with applications including sleep studies and health monitoring. “Whenever [clinicians or researchers] need to look at any brain signal, they can connect our device,” says co-author Hong Yeo, an engineer at the Georgia Institute of Technology. “It’s easy to use, wearable, and it’s wireless.” Yeo has been working for years to make EEG setups more portable and easy to use in everyday life.
Currently, in order to deal with motion artifacts, clinicians may attach more electrodes than strictly needed for redundancy, which can be inconvenient and time-consuming. Other researchers have investigated various ways that noise could be removed, including computational methods. A 2024 study suggested that connecting cables and changing skin contact were responsible for many motion artifacts.
How the Electrode Was Designed and Fabricated
The new electrode was designed in part to control costs. For example, based on material properties alone, gold would have been a good option for plating the microneedles, but gold is prohibitively expensive compared to the polymer coating in the current design.
This tiny electrode can be pressed into the scalp between hair follicles. Georgia Institute of Technology
The new sensor is an “interesting combination of different pieces of technology,” says Boris Stoeber, an engineer at the University of British Columbia, who was not involved in the research.
Fabrication steps include filling a microneedle mold under vacuum with a composite resin used in dentistry, curing the sensor with ultraviolet light, and laser-cutting into the cross shape. The microneedles are then coated with a highly-conductive polymer and heat treated. A dual-layer connecting wire is laser cut from copper foil and polyimide film into a curving form that the authors describe as “serpentine.”
Most of these processes appear scalable, says Stoeber, who has 25 years of experience with microneedle design and fabrication, often for drug delivery. However, the conductive polymer coating process appears unconventional, he says.
This initial study included only six participants, and there is more to learn about safety, efficacy, and functionality: for example, researchers must investigate how the device performs for people with different hair qualities or sensitivities to microneedles. And there may be practical hurdles to certain applications. For instance, if the sensor is being applied to the back of the head, as in the BCI tests described in the paper, a second person is needed to ensure that the device is attached properly to the scalp.
“We have to pinpoint the exact market and applications,” says Yeo, who is working on commercialization. He is open to suggestions, because, “It can be useful for many applications that I never thought of.”
