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

We describe the possibility of measuring sodium and potassium at the concentrations present in whole blood using lifetime-based sensing and phase-modulation fluorometry. The probe SBFO was shown to display changes in phase or modulation at sodium concentrations near 100 mM, and to be mostly independent of interfering effects due to potassium. The probe CD222 was found unsuitable for measurements of potassium in blood using intensity-ratio measurements, due to similar spectral changes induced by sodium. However, sodium at blood concentrations near 100 mM causes only a minor change in the lifetime 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, sodium causes only a modest change in the lifetime of the potassium probe PBFI, which displays potassium-dependent lifetimes. For both CD222 and PBFI, the presence of blood levels of sodium increases the apparent potassium dissociation constants into the blood physiological range. In total, these results demonstrated the possibility of lifetime-based sensing of sodium and potassium at the extracellular cation concentrations present in blood or blood serum.