HOMOGENEOUS IMMUNOASSAYS USING RARE-EARTH CRYPTATES AND TIME-RESOLVEDFLUORESCENCE - PRINCIPLES AND SPECIFIC ADVANTAGES FOR TUMOR-MARKERS

We have developed a new type of long lived fluorescent tracer the rare earth cryptates formed by the inclusion of a Eu3+ ion into the intra molecular cavity of a macrobicyclic ligand containing bipyridine units . This tracer is used in a new homogeneous assay format based on spect ral and temporal selectivity as well as on an amplification of the cry ptate Florescence. As a consequence of these features, the measurement of the specific signal is totally shielded from media interaction and corrected in real time for sample to sample optical variation. We sho w the example of a PSA assay where an analytical sensitivity of 0.03 n g/ml is obtained and an AFP assay where measurements in the first minu tes of the incubation allow a rapid estimation of the AFP concentratio n and therefore an immediate dilution of the samples if required These results illustrate the performance of this new homogeneous method and point out the specific advantages it allows in terms of sensitivity, precision and flexibility. It is therefore particularly well adapted f or the assay of analytes like tumor markers where both sensitivity and wide dynamic range are needed.