Performance of ultra-high-density microelectrode arrays

Imaging the electrical output activity of biological cells is important to gain an understanding of how cell networks process information. This has implications for the understanding of brain processing, such as that performed by the retina in encoding the visual scene. The performance and electrical quality of a state-of-the-art high-density 519-microelectrode array, that recorded simultaneously from hundreds of live retinal output cells (ganglion cells) is reported on. The fabrication process for these devices has been optimised and their electrical characteristics examined. The electrode arrays typically exhibit an impedance of ∼200 kΩ at 1 kHz and the RMS noise of the whole recording system is 7 μV with a signal to noise ratio of 20:1. With a view to direct stimulation of retinal ganglion cells, a low impedance Z=300 kΩ iridium oxide interface capable of delivering large currents Qcap=4 mC/cm2 to cells was also developed.