In the present paper, fabrication, characterization, and physiological applications of a solid-state pH
electrode are described. The pH sensing layer was based on an anodic electrodeposited
iridium oxide film (AEIROF). Sputtered
platinum electrodes (1 mm diameter) fabricated on flexible Kapton films or
platinum wires were used as planar or cylindrical supports. Each
electrode site was coated with
Nafion to attenuate the interference of anionic redox species and to protect the
electrode surface during in vivo measurements. Performance of the AEIROF was evaluated, for the first time, as a pH
electrode 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 electrodes. Linear pH responses were obtained in the pH range 2-10. The
electrodes 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 sensitivities for different species, such as Na+, K+, Li+, NH4+, Ca2+, Mg2+, dissolved
oxygen,
lactate, ascorbate, and
urate, 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 AEIROF pH
electrode and the previously described K+ and
lactate electrodes is presented as well.