TO-PRO®-3 stain is a carbocyanine monomer nucleic acid stain with far-red fluorescence similar to Alexa Fluor® 647 or Cy®5 dyes. It is useful as a nuclear counterstain and dead cell indicator, and is among the highest-sensitivity probes for nucleic acid detection.

Also available as a room-temperature-stable, ready-to-use solution: NucRed Dead 647 Ready Probes Reagent.
See other Ready Probes ready-to-use imaging reagents and accessories ›

Important Features of TO-PRO®-3 Stain Include:

• Ultrasensitive detection of dsDNA (double-stranded nucleic acids)
• Ideal for flow cytometry and fluorescence microscopy
• Long-wavelength fluorescence well separated from green and red fluorophores
• Excitation⁄Emission: 642⁄661 nm
• Cell impermeant

Many Applications
TO-PRO®-3 and the other monomeric cyanine stains have wide applicability due to their low background and bright fluorescence. Uses include staining of nucleic acids on solid supports, prestaining of samples for gel or capillary electrophoresis, viability detection and counterstaining in multiple-label experiments.

TO-PRO®-3 Stain has High Selectivity for Nuclear Over Cytoplasmic Staining
TO-PRO®-3 gives strong and selective staining of the nucleus in cultured cells and in paraffin sections. TO-PRO®-3 and other carbocyanine monomers have very strong binding affinity for dsDNA, with dissociation constants in the micromolar range.

Use TO-PRO®-3 Stain for 2-Color Viability Staining
Simultaneous labeling with a green-fluorescent SYTO® dye and cell-impermeant TO-PRO®-3 stain is frequently used to assess cell viability. TO-PRO®-3 and TOTO®-3 stains both have much greater extinction coefficients than DNA-bound propidium iodide.

Expand Your Options for Multicolor Labeling
The long-wavelength fluorescence of TO-PRO®-3 stain is well separated from that of commonly used fluorophores, such as our popular Alexa Fluor® dyes, Oregon Green®, fluorescein (FITC), rhodamine (TRITC), Texas Red™, coumarin (AMCA), Marina Blue™ and Pacific Blue™ dyes. Additionally, long-wavelength light–absorbing dyes such as TO-PRO®-3 stain have the advantage that their fluorescence is usually not obscured by the autofluorescence of tissues.
Explore other probes for the nucleus

Learn more about nucleic acid detection on gels, blots, and arrays.

Read more about cyanine dyes and other nucleic acid stains.

Find out more about viability and cytotoxicity assay reagents.

Plot the TO-PRO®-3 spectra and check spectral compatibility with other fluorophores