Alexa Fluor 488-conjugated antibodies absorb light maximally at 493 nm and fluoresce with a peak around 519 nm. In aqueous mounting media they are brighter than FITC, Cy2, and DyLight 488. Alexa Fluor 489 conjugates are recommended for maximum sensitivity for all immunofluorescence procedures requiring a green-fluorescing dye, except for protocols that include mounting in plastic mounting media.