Streptavidin, 1 mg. Vector Laboratories Streptavidin is isolated from Streptomyces avidinii by a specific affinity system, which results in a homogeneous, ultrapure streptavidin with very low non-specific binding characteristics. Unconjugated streptavidin is recommended for use in solid-phase assays and immunohistochemical applications when the technique of sequential addition of reagents (sandwich technique) is employed. This reagent has also been effectively employed in subtractive hybridization procedures.