Fluorescent europium chelate sta.

The europium chelate of 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (thenoyl-trifluoroacetone; TTA) is firmly bound to microorganisms. It fluoresces brightly at 613 nm with activation at 340 nm. Cells may be stained with 10(-3)m chelate in 50% ethyl alcohol, followed by washing with 50% ethyl alcohol. Equal or better stains are produced with 10(-3)m aqueous europium salt, water wash, and 10(-2)m aqueous TTA. A noncomplexing buffer should be used to maintain the pH at 6.5 to 6.8.