In-vivo applications of pH microelectrodes

Potentiometric microelectrodes have been widely used for pH measurements in many in-vivo applications. This chapter has provided an overview of these electrodes and a discussion of a number of practical challenges related to sensor designs, fabrication methods, and applications. 

Commercial silver/silver-chloride reference electrodes are available in a variety of styles and sizes. They are often used as the internal reference electrodes in glass pH and other ion-selective electrodes. Ag/AgCl microelectrodes formed from very thin silver wire have found extensive use, for example, in biomedical applications such as in vivo studies of biological fluids and intracellular measurements, because of the miniaturization possible with these electrodes. 

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. 

An evaluation of the pH sensor [52] in sheep, developed by Peterson et al. demonstrated its aptitude for in vivo blood pH measurement. Although not identical with the values obtained with an invasive microelectrode and with data obtained on withdrawn blood, the agreement between numerical data and trends is very good. It was not possible to say which of the measurements was the most correct. This demonstrates that the fiber-optic method is generally applicable for blood pH measurements in vivo, and gives as good an indication of pH levels as electrode methods. The pH of ewe blood as determined by an electrode, a blood gas analyzer, and a fiber-optic device is shown in Figure 18-9. 

---