14 July 2021
Tiny, Injectable Sensors Could Monitor Brain Activity without Surgery or Implants
System-on-a-nanoparticle are designed to convert the brain’s electrical activity to optical signals detectable outside the body
WASHINGTON — Researchers have developed nanoscale sensors that could be injected into the body to noninvasively track brain activity using light. The approach could one day offer a new way to study the brain or assess patients’ brain functioning without the need for surgery or implanted devices.
Ali Yanik’s lab at UCSC’s Baskin School of Engineering will report on the technology, called NeuroSWARM3, at the virtual OSA Imaging and Applied Optics Congress held 19-23 July. Neil Hardy, a graduate student in Yanik’s lab, is scheduled to present their findings on Tuesday, 20 July at 20:00 PDT. The congress is co-located with the OSA Optical Sensors and Sensing Congress.
“NeuroSWARM3 can convert thoughts (brain signals) to remotely measurable signals for high precision brain-machine interfacing,” said Yanik. “It will enable people suffering from physical disabilities to effectively interact with external world and control wearable exoskeleton technology to overcome limitations of the body. It could also pick up early signatures of neural diseases.”
The approach offers a new way to monitor electrical activity in the brain using a system-on-nanoparticle probe that is comparable in size to a viral particle. Neurons use electrical signals to convey information to each other, making these signals crucial to thought, memory and movement. While there are many established methods for tracking the brain’s electrical activity, most require surgery or implanted devices to penetrate the skull and interface directly with neurons.
The researchers named their new technology Neurophotonic Solution-dispersible Wireless Activity Reporters for Massively Multiplexed Measurements, or NeuroSWARM3.
The approach involves introducing engineered electro-plasmonic nanoparticles into the brain that convert electrical signals into optical signals, allowing brain activity to be tracked with an optical detector from outside the body.
The nanoparticles consist of a silicon oxide core measuring 63 nanometers across with a thin layer of electrochromically loaded poly (3, 4-ethylenedioxythiophene) and a gold coating 5 nanometer thick. Because their coating allows them to cross the blood-brain barrier, they could be injected into the bloodstream or directly into the cerebrospinal fluid.
Once in the brain, the nanosensors are highly sensitive to local changes in the electric field. In laboratory tests, in vitro prototypes of the NeuroSWARM3 were able to generate a signal-to-noise ratio of over 1,000, a sensitivity level that is suitable for detecting the electrical signal generated when a single neuron fires.
“We pioneered use of electrochromic polymers (e.g., PEDOT:PSS), for optical (wireless) detection of electrophysiological signals,” Yanik added. “Electrochromic materials known to have optical properties that can be reversibly modulated by an external field are conventionally used for smart glass/mirror applications.”
NeuroSWARM can be thought of nanoscale electrochromically loaded plasmonic (electro-plasmonic) antenna operated in reverse: instead of applying a known voltage, its optical properties are modulated by the spiking electrogenic cells within its vicinity. Hence, NeuroSWARM3 provides a far-field bioelectric signal detection capability in a single nanoparticle device that packs, wireless powering, electrophysiological signal detection and data broadcasting capabilities at nanoscale dimensions.
The optical signals generated by NeuroSWARM3 particles can be detected from outside of the brain using near-infrared light with wavelengths between 1,000-1,700 nm. The nanoparticles can function indefinitely without requiring a power source or wires.
Other researchers have explored a similar approach using quantum dots designed to respond to electrical fields. Comparing the two technologies, the researchers found NeuroSWARM3 generates an optical signal that is four orders of magnitude larger. Quantum dots required ten times higher light intensity and one hundred times more probes to generate a comparable signal.
"We are just at the beginning stages of this novel technology, but I think we have a good foundation to build on," said Yanik. “Our next goal is to start experiments in animals.”
In addition to Yanik, the co-authors of this study include UCSC graduate students Neil Hardy, Ahsan Habib, and undergraduate researcher Tanya Ivanov.
About the 2021 Imaging and Applied Optics Congress and Optical Sensors and Sensing Congress
The OSA Imaging and Applied Optics Congress (register) provides a comprehensive view of the latest developments in imaging and applied optical sciences, covering the forefront advances in imaging and applied optics as well as the application of these technologies to important industrial, military and medical challenges. The OSA Optical Sensors and Sensing Congress (register) will provide a forum for both the technical and applications sides of sensors to report the latest optical-based sensor advances, bring together major sensor developers and users, and provide a showcase for the latest sensor prototypes and products. These events will be presented in a virtual, web-conference format using a program schedule based on Pacific Daylight Time (PDT, UTC-07:00). Attendees have the option of viewing sessions live or streaming recorded sessions on demand.
About The Optical Society
The Optical Society (OSA) is dedicated to promoting the generation, application, archiving, and dissemination of knowledge in optics and photonics worldwide. Founded in 1916, it is the leading organization for scientists, engineers, business professionals, students, and others interested in the science of light. OSA’s renowned publications, meetings, online resources, and in-person activities fuel discoveries, shape real-life applications and accelerate scientific, technical, and educational achievement.