Steptavidin, a bacterial protein isolated from Streptomyces avidinii, is similar to egg-white avidin in its ability to bind biotin, and has been used as a replacement for egg-white avidin because of its more favorable chemical properties.
Conjugates of streptavidin are recommended for use with Biotin-SP-conjugated antibodies and Biotin-SP-conjugated ChromPure proteins.
Conjugate: Alexa Fluor® 488
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® 488 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.