alexa fluor 488 flourescent dye

Alexa Fluor® 488 Dye—A Superior Alternative to FITC

You have a choice when it comes to green-fluorescent dyes conjugates. The Alexa Fluor® 488 dye—with nearly identical spectral properties and quantum yield as 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.

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Seeing Green

Since its first synthesis in the 1870s, the fluorescein fluorophore has spread into a multitude of applications, including biological research. The fluorophore has much to recommend it: visible light excitation and emission, a high quantum yield, and pH sensitivity in the physiological range. However, as the uses of fluorescein spread and detection technology improved, some limitations began to appear. Although protein conjugates can be made using fluorescein, the fluorophore has a tendency to quench after only a few dyes are attached. These conjugates also tend to photobleach quickly, making it difficult to obtain images requiring longer exposure times.

A Cornucopia of Alexa Fluor® 488 Dye Conjugates

Invitrogen features a wide selection of Alexa Fluor® 488 dye conjugates, including a large selection of secondary antibody conjugates for your most demanding imaging applications.

Advantages of the Alexa Fluor® 488 Dye Conjugates

Introduced in 1997, the Alexa Fluor® 488 dye is the first dye in 100 years to seriously challenge fluorescein’s dominance as the green-fluorescent dye of choice:

  • A perfect spectral match for FITC filters—absorption—and emission profiles of Alexa Fluor® 488 and fluorescein are nearly identical, so there’s no need to change equipment, settings, or filters
    (Figure 1).
  • Brighter conjugate fluorescence—fluorescein conjugates rapidly quench as more fluorophores are added. Alexa Fluor® 488 dye allows more fluorophores to attached before self-quenching. This produces brighter conjugates (Figure 2) which means you can add less antibody and still get optimal results.
  • Superior photostability—allows more time for image observation and capture, permitting greater sensitivity and simplifying low-abundance target detection (Figure 3).

Figure 1FluoCells® prepared slide #6 showing a fixed, permeabilized, and labeled muntjac skin fibroblast. Mitochondria were labeled with anti–Oxphos Complex V inhibitor protein mouse IgG1 and visulaized using orange-fluorescent Alexa Fluor® 555 goat anti–mouse IgG. F-actin was labeled with green-fluorescent Alexa Fluor® 488 phalloidin, and the nucleus was stained with TO-PRO® 3 iodide (pseudocolored magenta). Image contributed by Michael S. Janes, Invitrogen.


Figure 2
—Comparison of the relative fluorescence of goat anti–mouse IgG antibody conjugates prepared from the 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.


Figure 3
—Photobleaching profiles of cells stained with Alexa Fluor® 488 or fluorescein conjugates of goat anti–mouse IgG antibody F(ab')2 fragment were used to detect HEp-2 cells probed with human antinuclear antibodies. Samples were continuously illuminated and images were collected every 5 seconds with a cooled CCD camera. Normalized intensity data demonstrate the difference in photobleaching rates.