New class of tetradentate β-diketonate-europium complexes that can be covalently bound to proteins for time-gated fluorometric application.

Luminescent lanthanide complexes that can be covalently bound to proteins have shown great utility as biolabels for highly sensitive time-gated luminescence bioassays in clinical diagnostics and biotechnology discoveries. In this work, three new tetradentate β-diketonate-europium complexes that can be covalently bound to proteins to display strong and long-lived Eu(3+) luminescence, 1,2-bis[4'-(1",1",1",2",2",3",3"-heptafluoro-4",6"-hexanedion-6"-yl)-benzyl]-4-chlorosulfobenzene-Eu(3+) (BHHBCB-Eu(3+)), 1,2-bis[4'-(1",1",1",2",2"-pentafluoro-3",5"-pentanedion-5"-yl)-benzyl]-4-chlorosulfobenzene-Eu(3+) (BPPBCB-Eu(3+)), and 1,2-bis[4'-(1",1",1"-trifluoro-2",4"-butanedion-4"-yl)-benzyl]-4-chlorosulfobenzene-Eu(3+) (BTBBCB-Eu(3+)), have been designed and synthesized as biolabels for time-gated luminescence bioassay applications. The luminescence spectroscopy characterizations of the aqueous solutions of three complex-bound bovine serum albumin reveal that BHHBCB-Eu(3+) has the strongest luminescence with the largest quantum yield (40%) and longest luminescence lifetime (0.52 ms) among the complexes, which is superior to the other currently available europium biolabels. The BHHBCB-Eu(3+)-labeled streptavidin was prepared and used for both the time-gated luminescence immunoassay of human prostate specific antigen and the time-gated luminescence microscopy imaging of a pathogenic microorganism Cryptosporidium muris . The results demonstrated the practical utility of the new Eu(3+) complex-based biolabel for time-gated luminescence bioassay applications.