Researchers at the University of Arkansas have developed a method to build electrodes for neural probes that have a much higher charge storage capacity than any previously announced. The research should lead to smaller, safer, and more sensitive neural probes.
The neural probe, made of gold and iridium oxide nanowires grown vertically on a polymer or titanium substrate, will improve the function and reliability of neural prosthetic devices. It has also displayed superior biocompatibility and mechanical strength compared to similar silicon structures.
“Our goal is to develop functional systems that can simultaneously stimulate nerves or muscle cells and record physiological changes in the human body,” said Hargsoon Yoon, research assistant professor in the College of Engineering and lead researcher on the project. “Our approach can minimize cell damage and even provide higher electrode efficiency than commonly used electrodes.”
The research team, based at the university’s Center for Wireless Nano-, Bio- and Info-Tech Sensor and Systems, developed probes that integrate free-standing, “hetero-structured” nanowires. Hetero-structured means the nanowires have an inner core and outer layer. Made of gold, the inner-core nanowires were grown vertically on titanium and polymer substrates. The outer, functional layer, made of iridium oxide, provides charge storage capacity for neural signal sensing and stimulation.
Researchers repeatedly demonstrated an electrical storage capacity of 48.6 Coulombs per square centimeter. Units of electrical charge are measured in Coulombs. Working with different materials, other major research groups, including teams at Stanford University and University of Southern California, have developed probes with less than half the storage capacity of the University of Arkansas probe.
Because storage capacity is directly related to density of electrical current needed to stimulate nerves and muscle cells, the probe can transfer charge into biological cells and tissues using less voltage – and less battery power – and thus can operate longer with less tissue and cell damage.