Used extensively in molecular and cell biology for detection and visualization of biomolecules. It combines the high-affinity binding of biotin to streptavidin with the strong fluorescent signal of fluorescein, enabling sensitive dual-labeling techniques. Commonly applied in fluorescence microscopy, flow cytometry, and ELISA assays to track proteins, nucleic acids, or cellular structures. The biotin moiety allows for amplification of signal through streptavidin-enzyme or streptavidin-fluorophore conjugates, while the fluorescein provides direct green fluorescence for real-time imaging. Ideal for multicolor labeling experiments where distinct fluorescent signals are required. Also used in affinity purification followed by fluorescent detection.