Biotin-4-fluorescein (N-(5-aminopentyl)biotinamide, trifluoroacetic acid salt) has been reported to be a superior fluorescent biotin derivative for accurate measurement of avidin and streptavidin in crude biological samples. Binding of biotin to avidin and streptavidin is high affinity, fast and noncooperative.    &lamba;Ex/&lamba; Em = 494/523 nm  Yellow solid soluble in DMSO, or pH>7 buffers  Store at 4°C and protect from light  C33H32N4O8S  MW: 644.7