Conjugates prepared with the amine-reactive Alexa Fluor 488 carboxylic acid, succinimidyl ester are significantly brighter and more photostable than fluorescein. The bright, green fluorescence of the Alexa Fluor 488 dye, which is spectrally similar to that of fluorescein, is pH independent from pH 4 to 10. Also available in a 5 mg unit size (Catalog number: A-20100).