A colored heat map based on the functional selectivity of opioid ligands at the DOR. The DMR signals of ligands in HEK-DOR cells with and without (i.e., buffer) pretreatment with probe molecules including PTX, CTX, U0126, SB202190, SP600125 and LY294002 were used to generate the heat map. All of the ligands in the library were assayed at 10 μM. The negative control (DMSO) was also included. To effectively visualize the impact of probe molecules, the net change for each ligand after pretreatment was obtained via subtraction, except for both the positive control (i.e., DMR in cells pretreated with the buffer vehicle only) and the ligand DMR in PTX-pretreated cells for which the raw data were used.