Cornell University researchers, alongside collaborators, have created a neural implant so diminutive that it can sit on a grain of salt. This innovative device is capable of wirelessly transmitting brain activity data in a living animal for over a year. The findings, published on November 3 in Nature Electronics, showcase the potential of microelectronic systems to operate at an unprecedentedly small scale, paving the way for advancements in neural monitoring and bio-integrated sensing.
The neural implant, known as a microscale optoelectronic tetherless electrode (MOTE), measures approximately 300 microns in length and 70 microns in width, making it the smallest of its kind that can wirelessly relay brain activity data. The project was co-led by Alyosha Molnar, the Ilda and Charles Lee Professor in the School of Electrical and Computer Engineering, and Sunwoo Lee, an assistant professor at Nanyang Technological University who initially worked on the technology as a postdoctoral associate in Molnar”s lab.
This device is powered by red and infrared laser beams that penetrate brain tissue without causing harm. The MOTE transmits data using tiny bursts of infrared light, which encode the brain”s electrical signals. A semiconductor diode composed of aluminum gallium arsenide harnesses light energy to power the circuit and emits light to convey the data. Additionally, a low-noise amplifier and optical encoder, constructed using similar semiconductor technology found in everyday microchips, support the device”s functionality.
“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 stated. “By employing pulse position modulation for the code—the same technique used in satellite optical communications—we can transmit data using minimal power while successfully retrieving the information optically.”
The researchers initially tested the MOTE on cell cultures before implanting it into the barrel cortex of mice, the brain area responsible for processing sensory information from whiskers. Over a year, the implant effectively recorded spikes of electrical activity from neurons, as well as broader patterns of synaptic activity, all while keeping the mice healthy and active.
Molnar explained that one of the primary motivations for developing this technology is to address the irritation caused by traditional electrodes and optical fibers in the brain. The movement of surrounding tissue can provoke an immune response, which the researchers aimed to minimize by creating a smaller device that still captures brain activity more rapidly than imaging systems, without requiring genetic modifications to the neurons for imaging purposes.
Moreover, Molnar suggested that the MOTE”s material composition might allow for electrical recordings from the brain during MRI scans, a capability that is largely unfeasible with current implants. This technology could also potentially be adapted for use in other tissues, such as the spinal cord, and may even be integrated with future advancements like opto-electronics embedded in artificial skull plates.
Molnar first envisioned the MOTE in 2001, but meaningful research progress only began about a decade ago when he began collaborating with members of Cornell Neurotech, a joint initiative between the College of Arts and Sciences and Cornell Engineering. The paper”s co-authors include Chris Xu, director of the School of Applied and Engineering Physics; Paul McEuen, John A. Newman Professor Emeritus in the Department of Physics; Jesse Goldberg, Dr. David Merksamer and Dorothy Joslovitz Merksamer Professor in Biological Sciences; and Jan Lammerding, professor in the Meinig School of Biomedical Engineering. This research received partial support from the National Institutes of Health, and fabrication work took place at the Cornell NanoScale Facility, which is supported by the National Science Foundation.
