A salt-grain-sized neural implant can record and transmit brain activity wirelessly for extended periods.
Researchers at Cornell University, working with collaborators, have created an extremely small neural implant that can sit on a grain of salt while wirelessly sending brain activity data from a living animal for more than a year.
The advance, reported in Nature Electronics, shows that microelectronic systems can operate at a scale far smaller than previously possible. This achievement opens the door to new approaches in long-term neural monitoring, bio-integrated sensors, and related technologies.
Shrinking neural implants to the extreme
The device, known as a microscale optoelectronic tetherless electrode, or MOTE, was developed under the joint leadership of Alyosha Molnar, a professor in the School of Electrical and Computer Engineering at Cornell, and Sunwoo Lee, an assistant professor at Nanyang Technological University.
Lee began working on the technology earlier as a postdoctoral researcher in Molnar's laboratory.
Wireless power and optical data transfer
The MOTE is powered by red and infrared laser light that can safely pass through brain tissue. It sends information back by emitting brief pulses of infrared light that carry encoded electrical signals from the brain.
A semiconductor diode made from aluminum gallium arsenide harvests the incoming light to power the circuit and also produces the outgoing signal. The system is supported by a low noise amplifier and an optical encoder, both built with the same semiconductor technology commonly used in modern microchips.
The MOTE is about 300 microns long and 70 microns wide.
"As far as we know, this is the smallest neural implant that will measure electrical activity in the brain and then report it out wirelessly," Molnar said. "By using pulse position modulation for the code – the same code used in optical communications for satellites, for example – we can use very, very little power to communicate and still successfully get the data back out optically."
New possibilities for brain and body monitoring
The researchers tested the MOTE first in cell cultures and then implanted it into mice's barrel cortex, the brain region that processes sensory information from whiskers. Over the course of a year, the implant successfully recorded spikes of electrical activity from neurons as well as broader patterns of synaptic activity – all while the mice remained healthy and active.
"One of the motivations for doing this is that traditional electrodes and optical fibers can irritate the brain," Molnar said. "The tissue moves around the implant and can trigger an immune response. Our goal was to make the device small enough to minimize that disruption while still capturing brain activity faster than imaging systems, and without the need to genetically modify the neurons for imaging."
Molnar said the MOTE's material composition could make it possible to collect electrical recordings from the brain during MRI scans, which is largely not feasible with current implants. The technology could also be adapted for use in other tissues, such as the spinal cord, and even paired with future innovations like opto-electronics embedded in artificial skull plates.
Molnar first conceived of the MOTE in 2001, but the research didn't gain momentum until he began discussing the idea about 10 years ago with members of Cornell Neurotech, a joint initiative between the College of Arts and Sciences and Cornell Engineering.
Reference: "A subnanolitre tetherless optoelectronic microsystem for chronic neural recording in awake mice" by Sunwoo Lee, Shahaboddin Ghajari, Sanaz Sadeghi, Yumin Zheng, Hind Zahr, Alejandro J. Cortese, Wenchao Gu, Kibaek Choe, Aaron Mok, Melanie Wallace, Rui Jiao, Chunyan Wu, Jesse C. Werth, Weiru Fan, Praneeth Mogalipuvvu, Ju Uhn Park, Shitong Zhao, Conrad Smart, Thomas A. Cleland, Melissa R. Warden, Jan Lammerding, Tianyu Wang, Jesse H. Goldberg, Paul L. McEuen, Chris Xu and Alyosha C. Molnar, 3 November 2025, Nature Electronics.
DOI: 10.1038/s41928-025-01484-1
The research was supported in part by the National Institutes of Health. Fabrication work was performed in part at the Cornell NanoScale Facility, which is supported by the National Science Foundation.
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