ISFET and fiber optic sensor technologies: in vivo experience for critical care monitoring.

A discrete sensor, configured as a tethered probe, placed in or near a local environment of interest to provide continuous measurement of the sensed variable, has been an enduring concept. 1-13,20-29 In addition to solid-state temperature and pressure, electrochemistry-based sensors for PO2, pH, and other specific ions, e.g., K + and Ca++, were early examples. Medical applications of sensor technologies have been seen as major market opportunities, and have had varied development efforts. Development and market success, however, has been elusive. In this paper the author reviews these efforts for two innovative sensor technologies that appeared in recent decades: ISFET sensors and fiber optic (‘optode’) sensors. By realizing the concepts of discrete sensors with micrometer dimensions, these developments effectively revolutionized sensor technology. These developments are primary examples of medical sensor technology that continues to evolve. The markets foreseen for these discrete sensors remain as possibilities.