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 DyeAbsorption
Max (nm) *
Max (nm) *
Emission Color †Extinction
Coefficient ‡
Alexa Fluor 350346442Blue19,000
Alexa Fluor 405402421Blue35,000
Alexa Fluor 430434539Yellow-green15,000
Alexa Fluor 488495519Green73,000
Alexa Fluor 514518540Green80,000
Alexa Fluor 532531554Yellow81,000
Alexa Fluor 546556573Orange112,000
Alexa Fluor 555555565Orange155,000
Alexa Fluor 568578603Red-orange88,000
Alexa Fluor 594590617Red92,000
Alexa Fluor 610612628Red144,000
Alexa Fluor 633632647Far-red159,000
Alexa Fluor 635633647Far-red140,000
Alexa Fluor 647650668Far-red270,000
Alexa Fluor 660663690Near-IR §132,000
Alexa Fluor 680679702Near-IR §183,000
Alexa Fluor 700702723Near-IR §205,000
Alexa Fluor 750749775Near-IR §290,000
Alexa Fluor 790782805Near-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 RedAlexa Fluor 568
Texas RedAlexa Fluor 594
Cy5Alexa Fluor 647
Cy5.5Alexa Fluor 680
Cy7Alexa Fluor 750