Color†	Absorb (nm)	Emit (nm)	MM (g/mol)	ε (cm-1M-1)
Alexa Fluor 350	blue	346	442	410	19,000
— 405	violet	401	421	1028	34,000
— 430	green	434	541	702	16,000
— 488	cyan-green	495	519	643	71,000
— 500	green	502	525	700	71,000
— 514	green	517	542	714	80,000
— 532	green	532	554	721	81,000
— 546	yellow	556	573	1079	104,000
— 555	yellow-green	555	565	~1250	150,000
— 568	orange	578	603	792	91,300
— 594	orange-red	590	617	820	90,000
— 610	red	612	628	1172	138,000
— 633	red	632	647	~1200	100,000
— 647	red	650	665	~1300	239,000
— 660	red	663	690	~1100	132,000
— 680	red	679	702	~1150	184,000
— 700	red	702	723	~1400	192,000
— 750	red	749	775	~1300	240,000
↑ = approximate color of the emission spectrum ε = extinction coefficient

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.^[1]

The excitation and emission spectra of the Alexa Fluor series cover the visible spectrum and extend into the infrared.^[2] 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,^[3] and to some extent the newer cyanine series.^[4] However, they are also more expensive. They are patented by Invitrogen (which acquired the company that developed the Alexa dyes, Molecular Probes) and are priced higher than the common dyes that are available from multiple manufacturers. On the other hand it has been reported that due to lower dosage, Alexa dyes offer a similar value plus the noted benefits.

Similar alternatives^[5] include the PromoFluor Dyes from PromoKine, the HiLyte Fluors from AnaSpec, DyLight Fluors from Pierce (Thermo Fisher Scientific), and the ATTO Dye series available from ATTO-TEC and Sigma-Aldrich.

Contents 1 History 2 Comparison with other dyes 3 References 4 External links

[edit] 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.

[edit] 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) ^[6] 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. [1] 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.

[edit] References

[edit] External links

• Additional data table with molecular structures