UC Irvine

The imbalance between L-glutamate (L-glu) and Gamma-aminobutyric acid (GABA), the most abundant excitatory and inhibitory neurotransmitters, respectively, has been hypothesized to be related to various neurological disorders such as autism spectrum disorder, seizures, and epilepsy. Despite the importance of monitoring their balance, tracking the L-glutamate and Gamma-aminobutyric acid (GABA) levels real-time is very challenging. Currently, microdialysis is being widely used for this purpose and while it shows great sensitivity and selectivity, there’s a several minutes of delay limited by diffusion and the probe used in the process is still very large, making it less feasible for measurements in local areas. Thus, electrochemical sensors have been the area of research to overcome these temporal and spatial resolution of microdialysis. With enzymatic and electrochemical reactions, it yields seconds of rapid response time and microfabrication technology allows several sensing points to be assembled in a few hundred micrometers allowing better spatial resolution.

Therefore, for the first half of this work, we have developed a highly sensitive electrochemical sensor for dual detection of L-glutamate and GABA. By electrochemical deposition of platinum nanoparticles, the overall active surface area was increased that led to higher sensitivity. Further, a self-referencing technique was adapted in order to achieve higher signal-to-noise ratio. Additionally, the sensor was fabricated using a flexible polyimide substrate for less brain damage along with easier handling compared to its ceramic counterparts. This dual L-glu:GABA sensor was validated in various conditions including in vitro, ex vivo with cell cultures and in vivo with anesthetized rodents. Furthermore, we tried improving its biocompatibility by exploring substitutional material for Ag/AgCl, a commonly used material for reference electrode in electrochemical systems. To replace Ag/AgCl, iridium oxide (IrOx) has been explored in terms of its biocompatibility and stability as a reference electrode. As a result, we were able to see IrOx’s capability to replace Ag/AgCl for better biocompatibility in long term measurements in vivo. Overall, our dual L-glutamate:GABA electrochemical biosensor has its unique features to enable accurate, real-time, and long-term monitoring of the E:I balance in vivo. Improvements in various aspects of the sensor have been made along with its validation in multiple settings. This new tool is expected to aid investigations of neural mechanisms of normal brain function and various neurological disorders.