DELFI® Eu-labeled streptavidin is intended for use as a generic reagent to detect biotin-labeled compounds, e.g. antibodies or antigens in various types of immunoassay or nucleic acid probes in hybridization assays based on solid-phase separation. The label, Eu³⁺, is measured using dissociation-enhanced time-resolved fluorometry.

The streptavidin is isolated from fermentation filtrates of Streptomyces avidinii and 1 mg of streptavidin binds approximately 10 μg of biotin. The preparation is supplied ready to use in 50 mmol/L Tris-HCl buffered saline solution. For DELFIA immunoassays, a final concentration of 100 ng/mL is recommended for the generation of a suitable signal.