Seph-PAO is the modified PAO attached a sepharose fluorophore and is used to detect the thioredoxin reductase (TrxR)[1].
References
[1] Dongzhu Duan, et al. Targeting Thioredoxin Reductase by Parthenolide Contributes to Inducing Apoptosis of HeLa Cells. J Biol Chem. 2016 May 6;291(19):10021-31. DOI:10.1074/jbc.M115.700591