The Alexa Fluor family of

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...

dyes is a series of dyes invented by

Molecular Probes Molecular Probes was a biotechnology company located in Eugene, Oregon specializing in fluorescence. The company was founded in 1975 by Richard and Rosaria Haugland in their kitchen in Minnesota, then moved briefly to Texas and finally to Oregon i ...

, now a part of

Thermo Fisher Scientific Thermo Fisher Scientific Inc. is an American supplier of scientific instrumentation, reagents and consumables, and software services. Based in Waltham, Massachusetts, Thermo Fisher was formed through the merger of Thermo Electron and Fisher Sc ...

, and sold under the Invitrogen brand name. Alexa Fluor dyes are frequently used as cell and tissue labels in

fluorescence microscopy A fluorescence microscope is an optical microscope that uses fluorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study the properties of organic or inorganic substances. "Fluorescence microscop ...

and cell biology. Alexa Fluor dyes can be conjugated directly to primary antibodies or to secondary antibodies to amplify signal and sensitivity or other biomolecules. The excitation and emission spectra of the Alexa Fluor series cover the

visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' or simply light. A typical human eye will respond to wa ...

and extend into the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

. The individual members of the family are numbered according roughly to their excitation maxima in nanometers.

History

Richard and Rosaria Haugland, the founders of

, are well known in biology and chemistry for their research into fluorescent dyes useful in biological research applications. At the time that Molecular Probes was founded, such products were largely unavailable commercially. A number of fluorescent dyes that are now widely used were discovered and developed in the laboratories of Molecular Probes.—dyes such as

Texas Red Texas Red or sulforhodamine 101 acid chloride is a red fluorescent dye, used in histology for staining cell specimens, for sorting cells with fluorescent-activated cell sorting machines, in fluorescence microscopy applications, and in immunohis ...

, Cascade Blue, Oregon Green, Marina Blue, and the Alexa Fluor family. The most famous of these, the Alexa Fluor family of dyes, were designed to improve upon properties of previously developed biological fluorescent dye families, and solve some of the issues that they possessed. The Alexa Fluor dyes were named after Alex Haugland, son of Richard and Rosaria Haugland. Molecular Probes was acquired in 2003 by

Invitrogen Invitrogen is one of several brands under the Thermo Fisher Scientific corporation. The product line includes various subbrands of biotechnology products, such as machines and consumables for polymerase chain reaction, reverse transcription, cl ...

, See also who worked to further expand the Alexa Fluor family by the addition of new dyes to fill gaps not covered in the emission spectrum. In 2008, Invitrogen and the Alexa Fluor product line became a part of the Life Technologies, after the Invitrogen merger with

Applied Biosystems Applied Biosystems is one of various brands under the Life Technologies brand of Thermo Fisher Scientific corporation. The brand is focused on integrated systems for genetic analysis, which include computerized machines and the consumables used w ...

. In 2014, Life Technologies was acquired by

, who revitalized the

name and brand, bringing the Alexa Fluor product line back under it.

Dyes and chemistry

The Alexa Fluor dyes were chemically synthesized through

sulfonation Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. Aryl sulfonic acids are used as detergents, dye, and drugs. Stoichiometry a ...

and additional chemical modifications made to the well known families of

coumarin Coumarin () or 2''H''-chromen-2-one is an aromatic organic chemical compound with formula . Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by a lactone-like chain , forming a second six-membered h ...

rhodamine Rhodamine is a family of related dyes, a subset of the triarylmethane dyes. They are derivatives of xanthene. Important members of the rhodamine family are Rhodamine 6G, Rhodamine 123, and Rhodamine B. They are mainly used to dye paper and inks ...

, and

cyanine Cyanines, also referred to as tetramethylindo(di)-carbocyanines are a synthetic dye family belonging to the polymethine group. Although the name derives etymologically from terms for shades of blue, the cyanine family covers the electromagnetic ...

dyes, and to the

xanthene Xanthene (9''H''-xanthene, 10''H''-9-oxaanthracene) is the organic compound with the formula CH2 6H4sub>2O. It is a yellow solid that is soluble in common organic solvents. Xanthene itself is an obscure compound, but many of its derivatives are us ...

family (of which the

fluorescein Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used ...

, an industry-standard, is a part). Sulfonation made the product Alexa Fluor dyes negatively charged and thus more

hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are ...

and soluble than their parent dyes; the additional modifications were aimed to improve dye performance in other areas. For example, Alexa Fluor 488, a sulfonated and otherwise chemically modified form of fluorescein, was designed to solve the well known issues of rapid

photobleaching In optics, photobleaching (sometimes termed fading) is the photochemical alteration of a dye or a fluorophore molecule such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between ...

and pH-dependent fluorescent intensity characteristic of the dye

fluorescein isothiocyanate Fluorescein isothiocyanate (FITC) is a derivative of fluorescein used in wide-ranging applications including flow cytometry. First described in 1942, FITC is the original fluorescein molecule functionalized with an isothiocyanate reactive group ( ...

Comparison with other dyes

The Alexa Fluor series dyes are less pH-sensitive and more photostable than the original dyes (

, etc.) from which they were synthesized. While extinction coefficients of each member of this line of dyes are known (see table), quantum yields and life times are not. Brightness comparisons are also generally favorable. Other commercial product lines provide alternatives to individual members of the line of Alexa Fluor Dyes. Comparisons with other dyes are less consistent, and also even more "delicate", depending on the conditions and techniques used. Such comparisons should be considered, depending on the conditions and techniques used, and the dye performance (signal, background, stability) needed.

Specific comparison studies

* Alexa Fluor 647 dye compared to dye Cy5,} in an application involving conjugation to DNA.

References

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External links