Metal chelates and methods of using them for time-resolved fluorescence

Abstract

β-diketone fluorescent tags are disclosed, particularly those enabling the use of excitation energy in the near visible or visible spectrum. In some cases, these tags allow the use of cost-effective excitation devices such as LED's. The compounds form fluorescent chelates (complexes) with lanthanide (III) rare earth metal ions (such as Eu3+). The fluorescent complex may be included in a latex microparticle, such as a styrene latex particle. Ideally, the complex has an absorption maximum λ equal to or greater than 360 nm, and the compound is characterized by a pKa<9.0. Kits and methods for detecting target molecules (e.g. immunoassays) are also disclosed. Such methods and kits typically use a ligand for binding to the target molecule and a labeling agent attached to the ligand. The fluorescent complexes described above are at least part of the labeling agent. Apparatus for detecting fluorescence from a sample includes an irradiating energy source that produces irradiating energy λ equal to or greater than 360 nm; a detector positioned to detect fluorescence from the sample; and a sample holder for holding the sample in position to be irradiated by the energy source. A light-emitting diode is preferably used as the irradiating energy source.