Good Readings Come in Threes: Understanding Electrodeposited Iridium Oxide for a Reproducible pH Microsensor...

Electrodeposited iridium oxide has been widely acknowledged as an effective pH sensing material of full pH sensing range, fast response time, and good chemical stability. However, a lack of fundamental understanding of the in-flask chemistry, electrodeposition chemistry, and storage chemistry limits the reproducibility of iridium oxide-based pH microsensors. Here, the iridium oxide films on pH microsensors are investigated from three perspectives: solution chemistry, electrodeposition chemistry, and film storage chemistry. We demonstrate that a high deposition efficiency is achieved with a high concentration of multi-Ir(IV)-center oligomers; the geometrical confinement of the iridium oxide film on microelectrode is enabled by lower electrodeposition potential; and the degradation of iridium complexes during film storage leads to time-dependent pH reading drift. The pH reading drift can be alleviated by laser-induced localized annealing of the iridium oxide films, which shows great potential for further fabrication and electrode patterning of iridium oxide microsensors and sensor arrays.