A Eu-MOF-Based Fluorescent Sensing Probe for the Detection of Tryptophan and Cu2+ in Aqueous Solutions

Abnormal tryptophan (Trp) metabolism can be used as an important indicator of chronic hepatitis, paranoia, Parkinson’s disease and other diseases. Deficiency or excessive accumulation of Cu2+ can cause diseases such as Wilson’s disease and Alzheimer’s disease. Eu-based metal-organic framework (Eu-MOF) was successfully prepared for fluorescence sensing of Trp and Cu2+ in an aqueous solution (pH = 7.4). Eu-MOF showed high selectivity and sensitivity for Trp and Cu2+ with detection limits of 0.22 µM and 0.09 µM and Ksv of 6.17 × 103 M− 1 and 2.37 × 104 M− 1 respectively. Trp and Cu2+ had overlapped UV absorption spectra with that of Eu-MOF and competed for the excitation light source. Trp also attenuated the antennae effect of organic ligands on Eu-MOF, thus quenching the red fluorescence of Eu-MOF. This study provides insights into the application of MOFs in bioanalysis and diagnostics. A water-stable Eu-MOF was synthesized with 2, 6-pyridine dicarboxylic acid (DPA) as ligand. Eu-MOF displayed good sensing properties for Trp and Cu2+ in aqueous solution (PH = 7.4). Lower detection limit of Eu-MOF for Trp and Cu2+ and larger Ksv for Cu2+ make Eu-MOF as a quench sensor for Trp and Cu2+. The fluorescence quenching of Eu-MOF by Trp and Cu2+ was explained experimentally and theoretically.