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: Cyanine Cy™5
Cy5 conjugates are excited maximally at 650 nm and fluoresce maximally at 670 nm. They can be excited to about 98% of maximum with a krypton/argon laser (647 nm line) or to about 63% of maximum with a helium/neon laser (633 nm line). Cy5 can be used with a variety of other fluorophores for multiple labeling due to a wide separation of its emission from that of shorter wavelength-emitting fluorophores. However, we recommend Alexa Fluor® 647 as the preferred far-red-fluorescing dye because it is brighter than Cy5 in aqueous mounting media. The reverse is true when mounting in non-polar, plastic mounting media, i.e. Cy5 is brighter than other far-red-fluorescing dyes, including Alexa Fluor® 647 and DyLight 650.