A cyclic peptide antenna ligand for enhancing terbium luminescence

We present here a cyclic peptide ligand, cy(WQETR), that binds to the terbium ion (Tb³⁺) and enhances Tb³⁺ luminescence intensity through the antenna effect. This peptide was identified through screening a cyclic peptide library against Tb³⁺ with an apparent EC₅₀ of 540 μM. The tryptophan residue from the peptide directly interacts with the Tb³⁺ ion, which provides access to a low-lying triplet excited state of the tryptophan. Direct excitation of this triplet state enables energy transfer to the Tb³⁺ ion and enhances Tb³⁺ luminescence intensity by 150 fold. We further showcase the application of this cy(WQETR)-Tb³⁺ system by demonstrating the detection of tromethamine with a detection limit of 0.5 mM.