Microelectrode Arrays for Simultaneous Electrophysiology and Advanced Optical Microscopy

Abstract

Advanced optical imaging techniques address important biological questions in neuroscience, where structures such as synapses are below the resolution limit of a conventional microscope. At the same time, microelectrode arrays (MEAs) are indispensable in understanding the language of neurons and are widely used in drug development and toxicology screening. The use of opaque electrodes in current MEAs, however, makes their combination with optical imaging challenging. Here, we report on transparent MEAs that are capable of recording action potentials from primary neurons and are compatible with confocal and super-resolution microscopy. The electrodes are made of the conducting polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) and are patterned by optical lithography, ensuring scalable fabrication with good control over device parameters. A thickness of 380 nm ensures low enough impedance and >75% transparency throughout the visible part of the spectrum making them suitable for artefact-free recording in the presence of with laser illumination. Using primary neuronal cells, the arrays recorded single units from multiple nearby sources with a signal-to-noise ratio of 7.7 (17.7 dB). Additionally, we were able to perform calcium (Ca2+) imaging, a measure of spontaneous activity of neuronal networks, using the newly designed transparent electrodes. Different biomarkers are imaged through the electrodes using widefield fluorescence, confocal and super-resolution microscopy, showing no qualitative differences or loss of spatial resolution compared to glass substrates. These transparent MEAs pave the way for harnessing the synergy between the superior temporal resolution of electrophysiology and the selectivity and high spatial resolution of optical imaging.