Time-resolved fluorometry: a sensitive method to quantify DNA-hybrids.

Europium and other lanthanides can be excitated with UV-radiation, whereafter the energy is released as fluorescence, delayed in time up to 1 ms after the excitation. Eu can be used as a sensitive label in biological assays. Here we report on the application of time-resolved fluorometry to detect nucleic acid hybrids. The probe DNA was tagged with a hapten, either a fluorene or a sulfone group. After hybridization the probe DNA was detected by a two-step immunological assay with the second antibody labelled with Eu. The method is quantitative with a detection limit of 0.3 pg of actual target regions of immobilized adenovirus genomic DNA. The label was also used in sandwich hybridization, which allowed analyzing nasopharyngeal mucus for the presence of adenovirus.