XFD350 NHS Ester (Succinimidyl Ester) is the same molecule to the Alexa Fluor® 350 NHS Ester (Alexa Fluor® is the trademark of ThermoFisher). It is a blue-fluorescent dye optimal for use with the 350 nm UV laser. XFD350 dye is water soluble and pH-insensitive from pH 4 to pH 10. The NHS ester (or succinimidyl ester) of XFD350 is the most convenient amine-reactive form for conjugating this dye to a protein or antibody.