Fabrication of pH-sensing iridium oxide nanotubes on patterned electrodes using anodic aluminum oxide nanotemplate

In this work, we introduced pH-sensing iridium oxide (IrO_x) nanotubes grown on metal electrodes which were patterned on a silicon substrate. The fabrication approach is compatible with conventional microfabrication processes for potential mass production. A layer of 900-nm aluminum was sputtered and anodized within an area of 50×100 μm² to create an anodic aluminum oxide (AAO) nanotemplate layer with controlled pore diameters in a range of 50-100 nm. Electrodeposition of IrO_x by potential cycling on the micro-scale electrode area produced tubes with an average diameter of 70 nm and length around 725 nm. Our result indicated the length and outer diameter of IrO_x nanotubes were determined by the nanopore profile of the supporting template. Owing to the potentiometric response to hydrogen ions, the micro-scale electrodes with modified IrO_x nanotube surface could be utilized as a micro pH sensor. A super-Nernstian response was achieved with a measured sensitivity of 74.3 mV/pH.