Lanthanide probes displays unique fluorescence properties, including long lifetime of fluorescence, large Stokes shift and narrow emission peak. These properties is highly advantageous to develop analytical probes for receptor-ligand interactions. Many lanthanide-based fluorescence studies have been developed for GPCRs, including CXCR1, insulin-like family peptide receptor 2, protease-activated receptor 2, β2-adrenergic receptor and C3a receptor.