Atomic layer deposited iridium oxide thin film as microelectrode coating in stem cell applications

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Abstract
Microelectrodes of microelectrode arrays (MEAs) used in cellular electrophysiology studies were coated with iridium oxide (IrOx) thin film using atomic layer deposition (ALD). This work was motivated by the need to find a practical alternative to commercially used titanium nitride (TiN) microelectrode coating. The advantages of ALD IrOx coating include decreased impedance and noise levels and improved stimulation capability of the microelectrodes compared to uncoated microelectrodes. The authors’ process also takes advantage of ALD’s exact process control and relatively low source material start costs compared to traditionally used sputtering and electrochemical methods. Biocompatibility and suitability of ALD IrOx microelectrodes for stem cell research applications were verified by culturing human embryonic stem cell derived neuronal cells for 28 days on ALD IrOx MEAs and successfully measuring electrical activity of the cell network. Electrode impedance of 450 kΩ at 1 kHz was achieved with ALD IrOx in the authors’ 30 μm microelectrodes. This is better than that reported for any uncoated microelectrodes with equal size, even equal to that of inactivated sputtered IrOx coating. Also, stimulation capability was demonstrated. However, further development, including, e.g., applying electrochemical activation, is needed to achieve the performance of commercial TiN-coated microelectrodes.

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