The bifunctional PE-Biotin conjugate demonstrates excellent avidin binding and strong fluorescence upon binding to a protein or nucleic acid target. It has avidin-binding properties similar to native biotin in terms of high affinity, fast association, and non-cooperative binding to avidin and streptavidin tetramers. PE-Biotin conjugate can be used for detecting and quantifying biotin binding sites of avidin, streptavidin or neutravidin. PE (R-Phycoerythrin), isolated from red algae, might be the brightest fluorophore. Its primary absorption peak is at 565 nm with secondary peaks at 496 and 545 nm. PE is the most intensely fluorescent phycobiliprotein, with quantum efficiencies probably in excess of 90%, and its orange fluorescence is readily visible by eye in any moderately concentrated solution.