Co-fluorescence of europium and samarium in time-resolved fluorimetric immunoassays

Abstract

In the presence of an excess of Y³⁺, the fluorescence intensities of Eu³⁺ and Sm³⁺, chelated with benzoyltrifluoroacetone (BTA) or thenoyltrifluoroacetone (TTA) in an aqueous solution containing 1,10-phenanthroline, were increased by factors ranging from 209- to 811-fold. This co-fluorescence phenomenon was used in a highly sensitive time-resolved fluorimetric detection of the lanthanides, Eu³⁺ and Sm³⁺. The detection limits of Eu³⁺ in the BTA- and TTA-based solutions were 4 and 15 fmol dm^–3, respectively. The detection limits of Sm³⁺ were 0.11 and 0.12 pmol dm^–3, respectively. The co-fluorescence enhancement systems were also applied in the double-lable time-resolved fluorimetric immunoassay of luteinizing hormone and follicle stimulating hormone using specific antibodies labelled either with Eu³⁺ or Sm³⁺. The co-fluorescence enhancement solution was superior as compared with the commercial ‘direct’ fluorescence enhancement solution based on the acidic solution of β-naphthoyltrifluoroacetone, trioctylphosphine oxide and Triton X-100, in respect to the signal level obtained and the sensitivity. It is suited to time-resolved fluorimetric immunoassays in which particularly high detection sensitivities are required, and it can also be used in double-label assays employing Eu³⁺ and Sm³⁺ chelate labels.