Nonisotopic receptor assay for benzodiazepine drugs using time-resolved fluorometry

A nonisotopic receptor assay for benzodiazepine drugs using a time-resolved fluorometric technique is described. A novel europium chelate-labeled benzodiazepine (Eu-1012-S) was prepared as a probe ligand for the binding assay based on the competitive inhibition of Eu-1012-S binding by benzodiazepine drugs to their receptors. In this system, the degree of the inhibition was proportional to the affinity of drugs for the receptor. Background fluorescence did not interfere with the measurement, due to the long-lifetime fluorescence of Eu-1012-S. The proposed nonisotopic assay may provide an alternative to radioreceptor assays of benzodiazepines in biological systems and could also be used to screen new benzodiazepine-like compounds from nature.