Electrical characterization of nanostructured 3D microelectrodes for retinal neuron stimulation

To provide visual information to people blinded by retinal degenerative diseases, retinal prosthetic devices based on multi-channel microelectrodes have been widely researched. A critical requirement of microelectrode is that the electro-electrolyte interface impedance should be small to generated sufficiently large current at a given voltage, to effectively stimulate retinal neurons. To improve the tradeoff, our research group developed an arrowhead-shaped 3D microelectrode, but the 3D microelectrode requires multi-step fabrication process. This paper presents a nanostructured 3D microelectrode with platinum-black which is simple to fabricate. Nanostructured 3D microelectrodes with the diameter of 25 um are fabricated and experimentally parameterized using a three-element circuit model. Maximum allowable current injection experiments are performed and compared to a theoretically estimated injection limit. All the electrical characteristics of the nanostructured 3D microelectrodes are compared with those of the arrowhead-shaped 3D microelectrodes. The electrode-electrolyte interface impedance of the nanostructured 3D microelectrode is 43.2 kH at 1 kHz, which is 79.7% lower than that of the arrowhead-shaped 3D microelectrode with the same diameter of 25 um. The maximum allowable current injection limit of the nanostructured 3D microelectrode is 392 μA, which is 429.7% higher than that of the arrowhead-shaped 3D microelectrode. These results show that the nanostructured 3D microelectrodes are more advantageous than the arrowhead-shaped 3D microelectrodes for high resolution retinal neuron stimulation.