Electrodeposited iridium oxide pH electrode for measurement of extracellular myocardial acidosis during acute ischemia

In the present paper, fabrication, characterization, and physiological appl ications of a solid-state pH electrode are described. The pH sensing layer was based on an anodic electrodeposited iridium oxide film (AEIROF), Sputte red platinum electrodes (1 mm diameter) fabricated on flexible Kapton films or platinum wires were used as planar or cylindrical supports. Each electr ode site was coated with Nafion to attenuate the interference of anionic re dox species and to protect the electrode surface during in vivo measurement s. Performance of the AEIROF was evaluated, for the first time, as a pH ele ctrode and proved to have a slightly super-Nernstian response with slope of -63.5 +/- 2.2 mV/pH unit for both wire and planar sputtered platinum elect rodes. Linear pH responses were obtained in the pH range 2-10, The electrod es have a working lifetime of at least 1 month with accuracy of about 0.02 pH unit and fast response time. The electrodes showed very low sensitivitie s for different species, such as Na+, K+, Li+, NH4+, Ca2+, Mg2+, dissolved oxygen, lactate, ascorbate, and mate, which are important for physiological applications, The electrodes were applied in extracellular pH measurements during brief regional ischemia in a swine heart and no-flow ischemia in an isolated rabbit papillary muscle. A first report on extracellular pH, K+, and lactate simultaneous measurements during no-flow ischemia using the AEI ROF pH electrode and the previously described K+ and lactate electrodes is presented as well.