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. 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.
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) *
Max (nm) *
|Emission Color †||Extinction|
|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.