The Alexa Fluor dyes—a series of superior fluorescent dyes that span the visible spectrum—represent a major breakthrough in the development of fluorescent labeling reagents.ref Benefits of the Alexa Fluor dyes and their conjugates include:

  • Brightness—Alexa Fluor conjugates exhibit more intense fluorescence than other spectrally similar conjugates.
  • Photostability—Alexa Fluor conjugates are more photostable than most other fluorescent conjugates, allowing more time for image capture.
  • Instrument compatibility—Absorption spectra of the Alexa Fluor conjugates are matched to the principal output wavelengths of common excitation sources.
  • Color selection—Alexa Fluor conjugates are available in several distinct fluorescent colors, ranging from blue to red to near-infrared (Figure 1, Table 1).
  • pH insensitivity—Alexa Fluor dyes remain highly fluorescent over a broad pH range.
  • Water solubility—Alexa Fluor reactive dyes have good water solubility, so protein conjugations can be performed without organic solvents, and the conjugates are relatively resistant to precipitation during storage.

Conventional fluorophores and their conjugates can often be replaced with spectrally similar Alexa Fluor dyes and conjugates without affecting optical filter choices or other instrumentation considerations (Table 2). Each of the Alexa Fluor dyes are listed in Table 1 and described in detail in Alexa Fluor Dyes Spanning the Visible and Infrared Spectrum—Section 1.3 and in the accompanying Section 1.3 data table.

Alexa Fluor Dye
Figure 1. Emission spectra for the Alexa Fluor dye series.

Table 1. Spectral properties of Molecular Probes Alexa Fluor dyes

Alexa Fluor Dye Absorption
Max (nm) *
Emission
Max (nm) *
Emission Color † Extinction
Coefficient ‡
Alexa Fluor 350 346 442 Blue 19,000
Alexa Fluor 405 402 421 Blue 35,000
Alexa Fluor 430 434 539 Yellow-green 15,000
Alexa Fluor 488 495 519 Green 73,000
Alexa Fluor 514 518 540 Green 80,000
Alexa Fluor 532 531 554 Yellow 81,000
Alexa Fluor 546 556 573 Orange 112,000
Alexa Fluor 555 555 565 Orange 155,000
Alexa Fluor 568 578 603 Red-orange 88,000
Alexa Fluor 594 590 617 Red 92,000
Alexa Fluor 610 612 628 Red 144,000
Alexa Fluor 633 632 647 Far-red 159,000
Alexa Fluor 635 633 647 Far-red 140,000
Alexa Fluor 647 650 668 Far-red 270,000
Alexa Fluor 660 663 690 Near-IR § 132,000
Alexa Fluor 680 679 702 Near-IR § 183,000
Alexa Fluor 700 702 723 Near-IR § 205,000
Alexa Fluor 750 749 775 Near-IR § 290,000
Alexa Fluor 790 782 805 Near-IR § 260,000
* Approximate absorption and emission maxima, in nm, for conjugates.
† Typical emission color seen through the eyepiece of a conventional fluorescence microscope with appropriate filters.
‡ Extinction coefficient of the reactive dye at emission maximum in cm-1M-1.
§ Human vision is insensitive to light beyond ~650 nm; it is not possible to directly view far-red– and near-IR–fluorescent dyes.

Table 2. Alexa Fluor dye alternatives to several common fluorophores

If you are using... Try this Alexa Fluor dye
Coumarin (AMCA) Alexa Fluor 350
Cy2 or Fluorescein (FITC) Alexa Fluor 488
Cy3 or Tetramethylrhodamine (TRITC) Alexa Fluor 555
Rhodamine Red Alexa Fluor 568
Texas Red Alexa Fluor 594
Cy5 Alexa Fluor 647
Cy5.5 Alexa Fluor 680
Cy7 Alexa Fluor 750
For Research Use Only. Not for use in diagnostic procedures.