Electrodeposited Iridium Oxide on Platinum Nanocones for Improving Neural Stimulation Microelectrodes

Microelectrodes for electrical neural stimulation play an important role in various medical and brain science applications, however, the shrinking size of microelectrodes leads to high electrode/tissue interfacial impedance and low charge injection capacity (CIC). In order to achieve safe, efficient and durable electrode performances, we proposed a layer-by-layer electrodeposition method to modify the bare platinum (Pt) microelectrodes. Combining the advantages of platinum gray (Pt gray) with iridium oxide (IrOx), herein a low impedance and high charge injection IrOx/Pt gray microelectrode was fabricated with nanoscale roughness. Morphological tests showed that nanocone-shaped Pt gray provided large effective surface area and hence good adhesion for dense IrOx deposition, which was beneficial for long-term mechanical stability of the composite coating. A typical microelectrode sample with the nanostructured IrOx/Pt gray coating had a low impedance down to 2.45 kΩ cm2 at 1 kHz, and a cathodic charge storage capacity (CSCc) up to 22.29 mC cm−2, which was about 6, 2.8 and 2.7 times higher than CSCc of those samples coated with bare Pt, Pt gray and IrOx, respectively. Furthermore, it demonstrated superior mechanical, electrochemical stability and CIC. These achievements indicate that composite coatings with well-controlled nanostructures may greatly enhance the performances of neural electrodes for various applications.