pH Indicators | Thermo Fisher Scientific

Intracellular pH is generally between ~6.8 and 7.4 in the cytosol and ~4.5 and 6.0 in the cell’s acidic organelles. Unlike intracellular free Ca²⁺ concentrations, which can rapidly change by perhaps 100-fold, pH inside a cell varies by only fractions of a pH unit, and such changes may occur quite slowly.

We offer a range of indicators for tracking intracellular pH in the cytosol or in particular organelles. Dye conjugates are available for organelle targeting and reactive dyes are also offered for constructing unique fluorescent probes for specific applications.

Select pH indicators

Indicators for tracking cytosolic pH

Red and green dyes for multiplexing
Choice of ratiometric or intensity-based measurement

Sensitive pH determinations can be made in a physiological range using either fluorescent intensity or ratiometric measurements. BCECF and its AM ester can be used to make ratiometric measurements within a narrow pH range, while pHrodo dyes provide signal intensity modulation from pH 2 to pH 9 and with a choice of fluorescent wavelengths.

U2OS cells labeled with pHrodo Green AM Intracellular pH Indicator U2OS cells incubated with 10 µM of pHrodo Green AM Intracellular pH Indicator for 30 minutes at room temperature. Images were captured using a confocal microscope.

Calibration & measurement

The pHrodo AM variety pack provides a choice of red or green indicators for pH measurement. When used together with the Intracellular pH Calibration Buffer Kit, the pHrodo dyes provide a complete solution for no-wash pH determination in live cells.

Intracellular pH determination using BCECF (left) and pHrodo Red (right) dye. pHrodo dyes are essentially non-fluorescent at neutral pH and extremely photostable, enabling reproducible measurements. They provide signal intensity modulation from pH 2 to pH 9 with a choice of fluorescent wavelengths.

Tracking pH in vesicles

Tracking internalization of fluorescent dextran is a routine method for analyzing pH changes in cellular compartments. Dextran conjugates of pHrodo dyes provide the most complete solution by allowing discrimination of vesicles from early endosomes to lysosomes, with no quench or wash required.

pHrodo dyes are essentially non-fluorescent at neutral pH and provide signal intensity modulation from pH 2 to pH 9 with a choice of fluorescent wavelengths. By conjugating pHrodo Red together with Rhodamine Green onto a 10,000 MW dextran, the dual-labeled probe also provides a reference signal for tracking.

Using pH change to monitor phagocytosis in MMM cells using pHrodo Green E. coli BioParticles Conjugate.

pH indicators selection guide

	pHrodo Green AM Intracellular pH indicator	pHrodo Red AM Intracellular pH indicator	2′,7′-Bis-(2-Carboxyethyl)-5-(and-6)-Carboxyfluorescein, Acetoxymethyl Ester (BCECF, AM)
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		pH-dependent ratio of emission intensity (detected at 535 nm) when the dye is excited at ~490 nm versus the emission intensity when excited at ~440
Range	Fluorescence increases from pH 8 to pH 4		pH range from 6.2 to 9.5
Standard filter set	FITC	TRITC	Requires excitation ratio to quantify pH
Fluorophore	pHrodo Green	pHrodo Red	BCECF
Ex/Em (mn)	509/533	560/585	~440-490/535
Cell permeant or impermeant?	Permeant	Permeant	Permeant
Usage notes	Load in cell media
Platforms	Flow cytometer, microplate reader, imaging		Microplate reader
Format	50 µL of 5 mM (1,000x)	50 µL of 5 mM (1,000x)	20 x 50 µg
Cat. No.	P35373	P35372	B1170

	pHrodo (AM) Variety pack		Intracellular pH Calibration Kit
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		Measure exact pH in live cells with pHrodo red AM and pHrodo green AM
Range	Fluorescence increases from pH 8 to pH 4		pH range from 4.5 to 7.5
Standard filter set	FITC	TRITC	Valinomycin and nigericin to create membrane pores
Fluorophore	pHrodo Green	pHrodo Red
Ex/Em (mn)	509/533	560/585
Cell permeant or impermeant?	Permeant	Permeant	Permeabilizes cell membrane
Usage notes	Load in cell media		Cellular pH equilibrates with medium
Platforms	Flow cytometer, microplate reader, imaging
Format	1 kit		1 kit
Cat. No.	P35380		P35379

	pHrodo Green Dextran, 10,000 MW	pHrodo Red Dextran, 10,000 MW	Dextran, BCECF, 10,000 MW, Anionic
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		pH-dependent ratio of emission intensity (detected at 535 nm) when the dye is excited at ~490 nm versus the emission intensity when excited at ~440
Range	Fluorescence increases from pH 8 to pH 4		pH range from 6.2 to 9.5
Vehicle	Dextran 10,000 MW	Dextran 10,000 MW	Dextran 10,000 MW
Standard filter set	FITC	TRITC	Requires excitation ratio to quantify pH
Fluorophore	pHrodo Green	pHrodo Red	BCECF
Ex/Em (nm)	509/533	560/585	~440-490/535
Cell permeant or impermeant?	Impermeant	Impermeant	Impermeant
Usage notes	Loaded by endocytosis, microinjection, patch pipette of pinocytic loading agent		Loaded by endocytosis, microinjection, patch pipette, or pinocytic loading agent
Platforms	Flow cytometer, microplate, Imaging		Imaging
Format	0.5 mg	0.5 mg	10 mg
Cat. No.	P35368	P10361	D1878

Cytoplasmic pH indicators

	pHrodo Green AM Intracellular pH indicator	pHrodo Red AM Intracellular pH indicator	2′,7′-Bis-(2-Carboxyethyl)-5-(and-6)-Carboxyfluorescein, Acetoxymethyl Ester (BCECF, AM)
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		pH-dependent ratio of emission intensity (detected at 535 nm) when the dye is excited at ~490 nm versus the emission intensity when excited at ~440
Range	Fluorescence increases from pH 8 to pH 4		pH range from 6.2 to 9.5
Standard filter set	FITC	TRITC	Requires excitation ratio to quantify pH
Fluorophore	pHrodo Green	pHrodo Red	BCECF
Ex/Em (mn)	509/533	560/585	~440-490/535
Cell permeant or impermeant?	Permeant	Permeant	Permeant
Usage notes	Load in cell media
Platforms	Flow cytometer, microplate reader, imaging		Microplate reader
Format	50 µL of 5 mM (1,000x)	50 µL of 5 mM (1,000x)	20 x 50 µg
Cat. No.	P35373	P35372	B1170

Cytoplasmic pH indicator kits

	pHrodo (AM) Variety pack		Intracellular pH Calibration Kit
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		Measure exact pH in live cells with pHrodo red AM and pHrodo green AM
Range	Fluorescence increases from pH 8 to pH 4		pH range from 4.5 to 7.5
Standard filter set	FITC	TRITC	Valinomycin and nigericin to create membrane pores
Fluorophore	pHrodo Green	pHrodo Red
Ex/Em (mn)	509/533	560/585
Cell permeant or impermeant?	Permeant	Permeant	Permeabilizes cell membrane
Usage notes	Load in cell media		Cellular pH equilibrates with medium
Platforms	Flow cytometer, microplate reader, imaging
Format	1 kit		1 kit
Cat. No.	P35380		P35379

Vesicle pH indicators

	pHrodo Green Dextran, 10,000 MW	pHrodo Red Dextran, 10,000 MW	Dextran, BCECF, 10,000 MW, Anionic
Readout	pHrodo dyes are non-fluorescent at neutral pH and increase in fluorescence emission intensity with acidification		pH-dependent ratio of emission intensity (detected at 535 nm) when the dye is excited at ~490 nm versus the emission intensity when excited at ~440
Range	Fluorescence increases from pH 8 to pH 4		pH range from 6.2 to 9.5
Vehicle	Dextran 10,000 MW	Dextran 10,000 MW	Dextran 10,000 MW
Standard filter set	FITC	TRITC	Requires excitation ratio to quantify pH
Fluorophore	pHrodo Green	pHrodo Red	BCECF
Ex/Em (nm)	509/533	560/585	~440-490/535
Cell permeant or impermeant?	Impermeant	Impermeant	Impermeant
Usage notes	Loaded by endocytosis, microinjection, patch pipette of pinocytic loading agent		Loaded by endocytosis, microinjection, patch pipette, or pinocytic loading agent
Platforms	Flow cytometer, microplate, Imaging		Imaging
Format	0.5 mg	0.5 mg	10 mg
Cat. No.	P35368	P10361	D1878

What are pHrodo indicators?

pHrodo dye is a novel, fluorogenic dye that dramatically increases in fluorescence as the pH of its surroundings becomes more acidic. The optimal absorption and fluorescence emission maxima of the pHrodo Green dye and its conjugates are approximately 509 nm and 533 nm, respectively, while pHrodo Red excites at 560 nm and emits at 585 nm. Both pHrodo Green and pHrodo Red can also be excited with the 488 nm argon-ion laser installed on most flow cytometers, microscopes, and microplate readers.

Phagocytosis in MMM cells. Cultured MMM macrophage cells were resuspended in Live Cell Imaging Solution containing 0.5 mg/mLpHrodo Red (left) or Green (right) Zymosan BioParticles reagent. After 90 minutes at 37C, NucBlue Live Stain was added to stain the nucleus, and the cells were imaged. BioParticles probes change from nonfluorescent to intensely fluorescent following cellular engulfment, allowing clear indication of phagocytic activity.

pHrodo red (left) and pHrodo Green (right) dye fluorescence emission spectra. The fluorescence emission spectra of pHrodo dye–labeled E. coli were measured in a series of 50 mM potassium phosphate buffers ranging in pH from 4 to 10. The E. coli were at a concentration of 0.1 mg/mL, and the readings were made on a Hitachi F4500 fluorometer, using an excitation wavelength of 532 nm.

Murine J774A.1 macrophages were labeled with pHrodo Green AM Intracellular pH Indicator and pHrodo Red 10,000 MW Dextran. The pH was clamped to the indicated values using the Intracellular pH Calibration Buffer Kit.

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For Research Use Only. Not for use in diagnostic procedures.