All-solid-state pH microelectrodes

Metal/metal oxides are the materials of choice for construction of all-solid-state pH microelectrodes. A further understanding of pH sensing mechanisms for metal/metal oxide electrodes will have a significant impact on sensor development. This will help in understanding which factors control Nemstian responses and how to reduce interference of the potentiometric detection of pH by redox reactions at the metal-metal oxide interface. While glass pH electrodes will remain as a gold standard for many applications, all-solid-state pH sensors, especially those that are metal/metal oxide-based microelectrodes, will continue to make potentiometric in-vivo pH determination an attractive analytical method in the future. 

Microelectrodes based on closed-end pH glass membranes were the first to be described in the literature (Cl). Hinke (H2) fiuther developed glass membrane microelectrodes with tip diameters of 10 im for the measurement of sodium and potassium. Various designs and approaches to the fiibri-cation of these all-glass microelectrodes have been taken over the years, and specific fabrication procedures may be found in the literature (H3, K3). Similarly, solid-state type electrodes based on pressed pellets of Ag2S with tip diameters on the order of 100 fim have been reported for the determination of Ag" ", S , I, Cl , Cu +, Br , etc. (C13). We have already discussed that such solid-state electrodes can foul when applied for direct measurements in biological systems, so the fabrication of these will not be discussed here. 

---