Our CELT-252 ligand is a highly potent fluorescent antagonist developed for hAT₁R testing with a K_i of 39.0 nM in radioligand binding assay. The product comes in a 10 µg vial that enables the preparation of 69 mL of 100 nM working solution to test AT₁R. Our fluorescent antagonist is ideal for visualization in confocal microscopy and high-content system experiments. Our CELT-252 ligand is potentially suitable for other fluorescence-based assays such as Fluorescence Polarization.