DPP-8/9 probe-1 (compound 20) is a fluorescent probe targeting Dipeptidyl Peptidase DPP8/9 , which can be selectively labeled and visualized in vitro by fluorescence microscopy Active DPP8/9. DPP-8/9 probe-1 contains a nitrobenzoxadiazole (NBD) tag and has high affinity and selectivity for DPP8/9 over related S9 family members ( IC 50 of 210 nM and 15 nM, respectively).