Fluorescein derivatives are the most common fluorescent reagents for biological research because of their high absorptivity, excellent fluorescence quantum yield, and good water solubility.

Fluorescein-based dyes and their conjugates have several performance characteristics that may facilitate or limit use in certain applications. Fluorescein displays:

  • A relatively high rate of photobleaching
  • Fluorescent signal that is sensitive to pH changes
  • A relatively broad fluorescence emission spectrum
  • Fluorescence quenching on conjugation to biopolymers
We offer a broad range of fluorescein conjugates and derivatives as well as a series of high-performance fluorophores with improved characteristics for labeling and detection.

Fluorescein dashboard

Initial brightness

Fluorescein is a bright green fluorphore that is sensitive to changes in pH and can photobleach rapidly unless an antifade agent is used. Anti-fluorescein antibodies can be useful in amplifying a weak signal. 

Photostability in buffer


Photostability in antifade


Fluorescein products

We offer a broad range of fluorescein products including protein and antibody labeling kits, primary and secondary antibody conjugates, bioconjugates, and more.

Learn more here:



HeLa cells were fixed and permeabilized using several Invitrogen products Image-iT Fixation/Permeabilization Kit then incubated with Anti-ATP Synthase Subunit IF1 and GAM-FITC secondary Ab. Cells were counterstained with NucBlue Live and ActinRed 555 then mounted using ProLong Gold Antifade Mountant and imaged using the EVOS M7000 Imaging System and a EVOS 40X Objective, coverslip-corrected

Fluorescein reactive dyes

Select dye-labeling chemistries for conjugation with the following reactive groups: 

AmineThiolAldehyde, ketone, carboxylate, or phosphate

Fluorescein protein/antibody labeling kits

Select an optimized labeling kit for your target antibody or protein:

Target proteinKitCat. No.
Site-specific antibody labeling
<1–20 µg mouse IgG1Zenon Fluorescein Mouse IgG1 Labeling KitZ25042
Conventional antibody/protein labeling
1 mg antibody/proteinFluorescein Antibody/Protein Labeling KitF10240

High-performance alternatives to fluorescein

Fluorescent conjugates

The Invitrogen Molecular Probes Alexa Fluor 488 dye—with spectral properties and quantum yield nearly identical to those of fluorescein isothiocyanate (FITC)—produces brighter, more photostable conjugates. These conjugates are ideal for imaging and other applications requiring increased sensitivity and environmentally insensitive fluorescence detection.

Monitoring pH

For pH monitoring the Invitrogen Molecular Probes pHrodo Green dye is almost nonfluorescent at neutral pH and fluoresces brightly in acidic environments. Unlike fluorescein, the minimal dye fluorescence at neutral pH also eliminates the need for wash steps and quencher dyes because any non-internalized dye will be essentially nonfluorescent.

 Comparison of the relative fluorescence of goat anti–mouse IgG antibody conjugates prepared from Alexa Fluor 488 dye and from fluorescein isothiocyanate (FITC). Conjugate fluorescence is determined by measuring the fluorescence quantum yield of the conjugated dye relative to that of a reference dye and multiplying by the dye:protein labeling ratio.

Not for resale. Super Bright Polymer Dyes are sold under license from Becton, Dickinson and Company.

Brilliant Ultra Violet™ and Brilliant Violet™ are trademarks or registered trademarks of Becton, Dickinson and Company or its affiliates, and is used under license.

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