Characterization of pH Sensors Based on Iridium Oxide and Gold Encapsulated Polypropylene Membranes

A porous gold membrane coated with iridium oxide nanoparticle has been developed on polypropylene (PP) for pH sensing. The electrical pH sensor is developed by an electroless plating technique that does not require high temperature processing, and therefore it could be built on paper substrates. The PP used as the substrate is flexible, robust, and immune to most chemical attacks. The pH sensing performance is characterized by the output potentials showing super-Nernstian sensitivities of -62 mV/pH and -61.6 mV/pH when tested in standard buffer pH solutions from acid to alkaline (2-4-7-10-13) and alkaline to acid (13-10-7-4-2), respectively. Hysteresis is tested and found to be highest at neutral pH 7, which commonly exists for metal oxide pH sensors. The sensor responds quickly and reaches stability in less than 4.5 s. Other pH sensor standardized performance parameters have also been obtained. Owing to its biocompatible and electrical properties; this pH sensor could be integrated with electronics in wearable, implant, and paper-based microfluidic devices for biomedical applications.