FITC vs Alexa 488

Richard Haugland richard.haugland at
Thu Mar 21 22:42:46 EST 2002

This is the comparison of the brightness of the Alexa Fluor 488 and fluorescein
conjugates that we publish, which indicates a closer to 1.5 to 2-fold advantage
of the Alexa Fluor 488 dye fluorescence intensity over fluorescein on this
secondary antibody. A principal advantage of the Alexa Fluor 488 dye over
fluorescein is its reduced photobleaching rate and the lack of pH sensitivity of
its fluorescence.

Figure 1.12 Comparison of the relative fluorescence of goat anti–mouse IgG
conjugates prepared from the Alexa Fluor 488 dye and from fluorescein
isothiocyanate (FITC). Conjugate fluorescence is determined by measuring the
fluorescein quantum yield of the conjugated dye relative to that of a reference
dye and multiplying by the dye:protein labeling ratio.


John Krowka wrote:

> On Molecular Probes' website are claims that Alexa 488 is 6-7 times brighter
> than FITC. Preliminary evidence from our conjugations of the same antibody
> with FITC or Alexa 488 indicate no advantage from using Alexa 488. Can
> anyone who compared Alexa 488 and FITC share their findings?
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