Development of luminescent lanthanide chelate labels for diagnostic assays

Luminescence properties of some of the lanthanide ions form the basis of highly sensitive diagnostic methods which employ their chelates as probes and time resolved fluorometry in the detection. In addition to bring highly luminescent, i.e., having an efficient light collection and energy transfer, photostability, good quantum yield and long excited state lifetime, an ideal luminescent chelate label must be small and highly hydrophilic and contain a functional group enabling its gentle coupling to the bioreagent. Certain qualifications have to be fulfilled when luminescent chelate labels are to be made, such as the optimal position of ligand triplet states, position and type of the binding arm, insulation of the coupling group from the energy absorbing moiety, a critical distance between the luminescent moiety and protein surface (in case of Tb) and elimination of all possible quenching routes associated with O-H and C-H stretching (in case of Eu). Lanthanide chelates have already proven to be very useful in highly sensitive immunoassays and simplified homogeneous assays. In addition, the new chelates developed permit materialization of numerous future ideas, such as miniaturized assay devices able to perform multi-parametric assays on sub-microliter volumes of samples.