Table 20.1 Molecular Probes pH indicator families, in order of decreasing pKa.

Parent Fluorophore pH Range Typical Measurement
SNARF indicators6.0–8.0Emission ratio 580/640 nm
HPTS (pyranine)7.0–8.0Excitation ratio 450/405 nm
BCECF6.5–7.5Excitation ratio 490/440 nm
Fluoresceins and carboxyfluoresceins6.0–7.2Excitation ratio 490/450 nm
LysoSensor Green DND-1894.5–6.0Single emission 520 nm
Oregon Green dyes4.2–5.7Excitation ratio 510/450 nm or excitation ratio 490/440 nm
LysoSensor Yellow/Blue DND-1603.5–6.0Emission ratio 450/510 nm
pHrodo dyesee below *Single emission 585 nm
* pHrodo succinimidyl ester exhibits a complex pH titration profile. Decreasing pH (from pH 9 to pH 2) produces a continuous (but nonlinear) fluorescence increase. This pH response profile typically changes upon conjugation of the dye to proteins and other biomolecules.