A water stable metal-organic framework, ZJU-108, was designed and successfully synthesized as a luminescent turn-up sensor, and it can discriminate tryptophan from other natural amino acids in aqueous solution. Because of the apparent lower singlet level of tryptophan compared with other amino acids, the singlet-singlet Förster energy transfer mechanism was applied to design a luminescent sensor. As a result, a selective MOF sensor for tryptophan was realized by choosing the ligand with the appropriate singlet energy level. As expected, ZJU-108 shows an excellent luminescence enhancement response to tryptophan over other natural amino acids with a detection limit of 42.9 nM. This work presents a new insight for designing turn-up MOF sensors and demonstrates the potential of ZJU-108 as a luminescent probe for the detection of tryptophan.