recording and stimulation performance of multi-electrode arrays passivated with plasma-enhanced atomic layer-deposited metal oxides.

To achieve an intimate contact between neuronal cells and the electrode in non-invasive platforms intended for neurological research, in this study, we fabricated a raised-type Au multi-electrode array (MEA) by employing nanoscale-thick indium-tin oxide (ITO; 50 nm) as a track layer and plasma-enhanced atomic layer-deposited (PEALD) AlO (30-60 nm) and HfO (20 nm) as passivation layers. The PEALD AlO-passivated Au MEA was subsequently modified with electrodeposited AuPt nanoparticles (NPs) and IrO to demonstrate the passivation capability and chemical resistance of AlO to Au-, Pt-, and IrO NP-containing electrolytes. AlO-passivated and IrO/AuPt-modified MEAs could resolve optogenetically activated spikes and spontaneous activities with a root-mean-square noise level of 2.8 ± 0.3 μV generated by the primarily cultured hippocampal neurons transfected with viral vectors. PEALD AlO exhibited a poor resistance to the Ag leaching environment (concentrated nitric acid maintained at 70 °C); therefore, a nanoporous Au (NPG) structure could not be implemented on the Au MEA passivated with AlO. By depositing a 20 nm-thick HfO over a 40 nm-thick AlO layer, the NPG structure could be implemented on the Au MEA, confirming the chemical resistance of HfO to the Ag leaching environment. The nontoxicity of AlO and HfO was confirmed by the successful primary culture of dissociated hippocampal neurons and electrophysiological studies performed using a hippocampal slice. Considering the advances in ALD technology and the vast number of metal oxides, these results extend the application of ALD metal oxides from water barriers for biomedical implants to passivation layers for MEAs.