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

Parent Fluorophore pH Range Typical Measurement
SNARF indicators 6.0–8.0 Emission ratio 580/640 nm
HPTS (pyranine) 7.0–8.0 Excitation ratio 450/405 nm
BCECF 6.5–7.5 Excitation ratio 490/440 nm
Fluoresceins and carboxyfluoresceins 6.0–7.2 Excitation ratio 490/450 nm
LysoSensor Green DND-189 4.5–6.0 Single emission 520 nm
Oregon Green dyes 4.2–5.7 Excitation ratio 510/450 nm or excitation ratio 490/440 nm
LysoSensor Yellow/Blue DND-160 3.5–6.0 Emission ratio 450/510 nm
pHrodo dye see 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.