Flexible and Transparent Microelectrode Array for Simultaneous 2-Photon Imaging and Electrical Recordings

Combining two modalities, optical imaging and electrical recordings of neural cells, can shed light on a more profound understanding of neural circuits. Microelectrode arrays with high optical transparency in the near-infrared (NIR) and high electrical conductivity are required to enable simultaneous 2-photon imaging and electrical recording. A transparent microelectrode array allows us to perform imaging and electrical recording at the exact location for improved correlation between the two modalities, with imaging having a better spatial resolution and electrical recording having a better temporal resolution. We present an ITO-based transparent microelectrode array's design, fabrication, and testing. The microelectrode array has 16 recording sites, with each electrode size of 20 µm x 20 µm. The microelectrode array uses 3 µm parylene-C as a substrate and encapsulation layer maintaining excellent flexibility. Bending tests for different radii are performed to characterize the array's flexibility. The 2-photon imaging through the electrode array shows optical transparency at the desired wavelength of 920 nm. Electrochemical impedance spectroscopy (EIS) is done to characterize the electrical characteristics of the microelectrode array. Finally, the simultaneous 2-photon imaging and electrical recording through the array on a head-fixed animal is underway for the final testing of the microelectrode array. The microelectrode array is connected to a custom PCB using heat seal connectors for further connection to the data acquisition system.