Wireless IrO ₂ Electrochemical Sensor System for Real-Time pH Monitoring in Microliter Volumes

Accurate pH measurement in microliter volumes is essential for real-time chemical and biological analysis, underpinning modern portable and point-of-care diagnostics. Here, we present a wireless electrochemical pH sensor system based on nanostructured iridium oxide (IrO₂) electrodeposited onto electron-beam-evaporated, photolithographically patterned gold electrodes (EBLG) and integrated with a low-power Bluetooth potentiostat for continuous, real-time pH monitoring. FESEM, Raman, and XPS confirm uniform spherical IrO₂ nanostructures with mixed Ir³⁺/Ir⁴⁺ states that are conducive to potentiometric transduction. The IrO₂/EBLG sensor exhibited near-Nernstian sensitivity (69.7 mV/pH) across a pH range of 2-9, a fast step response (∼10 s), negligible hysteresis during bidirectional cycling, and exceptionally low potential drift (∼0.12-0.28 mV/h over 12 h). It demonstrates high selectivity toward H⁺ ions against common physiological interferences with excellent reproducibility and robust long-term stability. The hand-held module wirelessly streams real-time potential data to a smartphone, enabling accurate pH quantification in microliter-scale biological, food, and environmental samples. Measurements showed strong agreement with a commercial microelectrode pH meter, with no statistically significant difference (p > 0.05; Bland-Altman and paired t-test). Overall, the IrO₂/EBLG platform combines miniaturization, stability, and wireless functionality, offering a reliable and scalable solution for decentralized pH sensing and paving a promising route toward future wearable, field-deployable, and environmental pH monitoring systems.