Layer-by-layer assembled nanorough iridium-oxide/platinum-black for low-voltage microscale electrode neurostimulation

• A low impedance and high charge-injection material with an enhanced surface area is proposed.
• A layer-by-layer assembly of IrOx/Pt-black with nanoroughness is fabricated.
• IrOx/Pt-black has half the impedance and 2.4 times QCDC of a same-sized flat-IrOx.
• In vivo electrical stimulation of the sciatic nerve of a mouse is demonstrated using a low voltage IrOx/Pt-black plated microelectrode.

Electrical neural stimulating electrodes play an important role in medical applications and improving health/medical conditions. However, size reduction for low-invasive electrodes creates issues with high electrolyte/electrode interfacial impedance and low charge-injection characteristics, which makes it impossible to stimulate neurons/cells. To overcome these limitations, we propose an electrode material for low-voltage microscale electrode neurostimulation that combines the advantages of low impedance of iridium oxide (IrOx) with the enhanced surface area of platinum black (Pt-black). Based on a simple, rapid, low-temperature electroplating process, herein a low impedance and high charge-injection electrode is fabricated by a layer-by-layer assembly of IrOx/Pt-black with nanoscale roughness. The assembled nanorough-IrOx/Pt-black electrode has an impedance of  32 Ω cm2 at 1 kHz and a charge-injection delivery capacity (QCDC) of 46.7 mC cm−2, which are 0.5 and 2.4 times the values for the same-sized IrOx/flat-Pt electrode, respectively. The stimulation capability of the nanorough-IrOx/Pt-black plated microelectrode is confirmed by in vivo stimulations of the sciatic nerve of a mouse. The threshold voltages of 8-μm-diameter and 11-μm-diameter electrodes are 700 mV and 300 mV, respectively. However, increasing the diameter of high QCDC nanorough-IrOx/Pt-black can further reduce the stimulation voltage. Consequently, nanorough-IrOx/Pt-black is applicable to low-voltage microscale electrode neurostimulations for powerful in vivo/in vitro electrophysiological measurements.