Laser-carbonized Electrodes on Implantable CMOS-based Imaging Device for Simultaneous Deep-brain Optical and Electrophysiological Measurements

Optical and electrophysiological methods are widely used in neuroscience to study brain activity.Each technique has its own strengths and weaknesses that complement each other to provide a more comprehensive understanding of neuronal activity.To this end, we developed an implantable CMOS image sensor device with an integrated carbon electrode for the simultaneous measurement of fluorescence and extracellular signals.The device is composed of a 450 × 1660 µm CMOS chip and micro-LED secured to a flexible printed circuit substrate.The chip has an imaging surface measuring 900 × 300 µm 2 , comprising 120 × 90 pixels recording at 10 frames per second.An absorption filter film was placed on top of the imaging surface to block excitation light.The device was coated with parylene-C for waterproofing and, finally, the coating film was readily turned into carbon electrodes by laser carbonization.We characterized the lasercarbonized electrodes by cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy to confirm carbonization.We then demonstrated simultaneous in vivo recording of fluorescence and extracellular signals in hippocampus CA1 using the device.