Abstract

Two independent parameters of physiological significance, temperature and pH, were remotely monitored simultaneously in real-time using a single fiber optic probe. The phosphorescence and fluorescence lifetimes of alexandrite and seminaphthofluorescein (SNAFL-2) indicators, respectively, were probed using a dual-frequency synthesized frequency-domain excitation signal. Heterodyne modulation of the fluorescence detector gain recovered the fluorescence emission modulation and phase at both widely separated excitation frequencies simultaneously using low-speed computer A/D hardware. The compact system employed either a green He-Ne laser or a super bright LED for fluorescence excitation. The accuracy of the temperature and pH measurements were 0.31 °C and 0.05, respectively. By choosing appropriate fluorescence indicator lifetimes, additional physiological sensors could be added. This technology has potential applications in minimally invasive medical diagnosis and patient monitoring.

© 1998 Optical Society of America