XFD488 is manufactured by AAT Bioquest, and it has the same chemical structure of Alexa Fluor® 488 (Alexa Fluor® is the trademark of ThermoFisher). XFD488 NHS Ester (Succinimidyl Ester) has the same molecule as Alexa Fluor® 488 NHS Ester (#A20000 and A20100 from ThermoFisher). It is a bright green-fluorescent dye optimal for use with the 488 nm Argon laser. XFD488 dye is water soluble and pH-insensitive from pH 4 to pH 10. XFD488 NHS ester (or succinimidyl ester) is the most convenient amine-reactive form for conjugating this dye to a protein or antibody. Although the Alexa Fluor® 488 NHS Ester is one of the most common green fluorescent labeling dyes, its purity has been quite challenging. ThermoFisher provides it with purity of ~50-60% while a few other vendors offer it at even lower purities. Among all the impurities, we noted that the Bis-NHS ester of XFD488 is quite detrimental since it could give a non-fluorescent product. This high purity XFD488 NHS ester is free of the detrimental XFD488 Bis-NHS ester impurity with the minimal purity of >75%.