Iridium Oxides Based Potentiometric Sensor for pH Monitoring in Biological Samples

The fabrication and long-term application of a pH Au microelectrode based on an iridium oxide film are reported. A uniform iridium oxide film with a typical thickness of around 1 µm was coated on the microelectrode surface through a 2-step procedure involving electrodeposition at constant potential and further continuous voltammetric scans. A super-Nernstian slope of around 77 mV per pH unit was found from open circuit potential measurements in a broad pH range (2 to 10) in 0.01 mol L-1 phosphate buffer. It was demonstrated experimentally that the short-term pH precision of the IrOx sensor is ± 0.1 pH. The response stability was maintained in the physiological pH range, and the sensor exhibited excellent reproducibility, long-term stability, and a short response time of < 10 s. The results reported in this work confirmed that iridium oxide showed very promising pH sensing performance and can serve as an electrode material for detecting local pH changes in samples of increased complexity, such as juice fruits, culture medium, synthetic urine, and blood.