Homogeneous Phosphodiesterase and Hybridization Assays Using Europium Cryptate: Oligonucleotide Conjugates

Upon conjugation to single-stranded oligonucleotides, a europium cryptate (Eu³⁺ tris-bipyridine) showed a marked increase in its fluorescence lifetime and was much less sensitive to fluorescence quenching by uric acid. This behavior was shown to be moderately dependent on the length and sequence of the oligonucleotide and all the single-stranded oligonucleotides studied displayed similar behavior. In contrast, a cryptate moiety attached to a double-stranded oligonucleotide did not display such an increase in its fluorescence lifetime and was quenched in presence of uric acid. Taking advantage of this unique behavior characterizing single-stranded K-ODN conjugates, a new concept of dosage based on the modulation of the cryptate fluorescence by a quencher was set up. This fluorescence quenching assay involving a single fluorescent label was applied to the monitoring of hybridization reactions and detection of a phosphodiesterase activity.