Iridium oxide on indium-tin oxide nanowires: An all metal oxide heterostructured multi-electrode array for neuronal interfacing

All metal oxide heterostructured multielectrode arrays consisting of indium-tin oxide nanowires (ITO NWs) and an iridium oxide (IrOx) layer were fabricated. The needle-type ITO NWs were grown on an ITO electrode using a radio frequency magnetron sputtering technique followed by electrodeposition of an IrOx layer. The major advantage of this fabrication technique is in its simplicity because it does not require templates and seed layers to grow the ITO NWs. A transmission electron microscope found the IrOx to be uniformly electrodeposited over the surface of the ITO NW. After the electrodeposition process, the charge storage capacitance (CSC) of the ITO NW electrode increased from 0.09 to 4.25 mC cm−2, and the IrOx/ITO NW electrode exhibited a charge injection limit of 1.9 mC cm−2 and CSC utilization efficiency of approximately 45%. The stimulation performance of the IrOx/ITO NW electrode was confirmed using rat hippocampal slices, which exhibited a higher negative peak amplitude in the field excitatory postsynaptic potential when stimulated by a single pulse, and more effectively induced long-term potentiation via a theta burst stimulation compared with an ITO NW electrode. These results indicate that the synergetic combination of ITO NWs and a very thin IrOx layer enhanced the performance of the stimulus.