Potassium and sodium measurements at clinical concentrations using phase-modulation fluorometry

We describe the possibility of measuring sodium and potassium at the concen trations present in whole blood using lifetime-based sensing and phase-modu lation fluorometry. The probe SBFO was shown to display changes in phase or modulation at sodium concentrations near 100 mM, and to be mostly independ ent of interfering effects due to potassium. The probe CD222 was found unsu itable for measurements of potassium in blood using intensity-ratio measure ments, due to similar spectral changes induced by sodium. However, sodium a t blood concentrations near 100 mM causes only a minor change in the lifeti me of CD222, Hence, CD222 and lifetime-based sensing can be used to measure blood levels of potassium in the presence of 130 mM sodium. Similarly, sod ium causes only a modest change in the lifetime of the potassium probe PBFI , which displays potassium-dependent lifetimes. For both CD222 and PBFI, th e presence of blood levels of sodium increases the apparent potassium disso ciation constants into the blood physiological range. In total, these resul ts demonstrated the possibility of lifetime-based sensing of sodium and pot assium at the extracellular cation concentrations present in blood or blood serum. (C) 1999 Elsevier Science S.A. All rights reserved.