Alexa Fluor

The Alexa Fluor family of fluorescent dyes is produced by Molecular Probes, a subsidiary of Invitrogen. Alexa Fluor dyes are typically used as cell and tissue labels in fluorescence microscopy and cell biology. [cite web | title = Alexa Fluor Dyes Spanning the Visible and Infrared Spectrum
url = http://probes.invitrogen.com/handbook/sections/0103.html | date = 2007-06-06 | accessdate = 2007-08-13]

The excitation and emission spectra of the Alexa Fluor series cover the visible spectrum and extend into the infrared. [cite web | title = The Alexa Fluor Dye Series
url = http://probes.invitrogen.com/handbook/boxes/0442.html | publisher = Molecular Probes, Inc. | date = 2006-04-06 | accessdate = 2007-08-13] The individual members of the family are numbered according roughly to their excitation maxima (in nm).

Alexa Fluor dyes are synthesized through sulfonation of coumarin, rhodamine, xanthene (such as fluorescein), and cyanine dyes. Sulfonation makes Alexa Fluor dyes negatively charged and hydrophilic. Alexa Fluor dyes are generally more stable, brighter, and less pH-sensitive than common dyes (e.g. fluorescein, rhodamine) of comparable excitation and emission, [cite journal |author=Panchuk-Voloshina N, Haugland RP, Bishop-Stewart J, "et al" |title=Alexa dyes, a series of new fluorescent dyes that yield exceptionally bright, photostable conjugates |journal=J. Histochem. Cytochem. |volume=47 |issue=9 |pages=1179–88 |year=1999 |pmid=10449539 |url = http://www.jhc.org/cgi/content/full/47/9/1179] and to some extent the newer cyanine series.cite journal |author=Berlier JE, Rothe A, Buller G, "et al" |title=Quantitative comparison of long-wavelength Alexa Fluor dyes to Cy dyes: fluorescence of the dyes and their bioconjugates |journal=J. Histochem. Cytochem. |volume=51 |issue=12 |pages=1699–712 |year=2003 |pmid=14623938 |url = http://www.jhc.org/cgi/content/full/51/12/1699] However, they are also more expensive. They are patented by Invitrogen (which acquired the company that developed the Alexa dyes, Molecular Probes) and thus are priced higher than the common dyes that are available from multiple manufacturers.

Similar alternatives [cite web | title = Alexa Fluor Dye Comparison to Alternatives | url = http://www.invitrogen.com/etc/medialib/en/filelibrary/cell_tissue_analysis/pdfs.Par.69135.File.dat/BioProbes56-AlexaFluor488.pdf | date = 2008-06 | accessdate = 2008-05-29] include the HiLyte Fluors from AnaSpec, DyLight Fluors from Pierce (Thermo Fisher Scientific), and the Atto series from Atto-Tec and sold by Sigma-Aldrich.

History

The Alexa Fluor dyes were named after Alex Haugland, son of the founders of Molecular Probes, Richard and Rosaria Haugland. The "Marina Blue" dye was named after their daughter, Marina.

Comparison with other dyes

The Alexa series dyes are less pH-sensitive and more photostable than the original dyes (fluorescein, rhodamine, etc.) from which they were synthesized.

However, brightness comparisons are not presently available. Brightness is commonly measured as a product of extinction coefficient (absorption efficiency) and quantum yield (emission efficiency) [cite journal |author=Souslova EA, Belousov VV, Lock JG, Stromblad S, Kasparov S, Bolshakov AP, Pinelis VG, Labas YA, Lukyanov S, Mayr LM, Chudakov DM |title=Single fluorescent protein-based Ca2+ sensors with increased dynamic range |journal=BMC Biotechnol. |volume=7 |issue=7 |pages=37 |year=2007 |pmid=17603870 |url = http://www.biomedcentral.com/1472-6750/7/37 |doi=10.1186/1472-6750-7-37] While extinction coefficients are known (see the table above), the quantum yields of the Alexas have not been published by Molecular Probes.

In one case, a third party has compared one Alexa with another commonly used dye. This was a comparison of Cy5 and its Alexa with similar wavelength, Alexa 647, with the dyes conjugated to DNA. [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=17873405&ordinalpos=6] This study found that Cy5 is brighter, but less photostable than Alexa 647.

Therefore presently it is difficult to quantitatively choose the best dye for a particular application and in many cases empirical testing is in order.

References

External links

* [http://probes.invitrogen.com/servlets/datatable?item=30005&id=38089 Additional data table with molecular structures]