A Europium MOF-based turn-off fluorescent sensor for tryptophan detection in human serum, urine and lake water

This work presents a turn-off fluorescence sensor [Eu(SIP)(H2O)4] (Eu-MOF, H3SIP ​= ​5-sulfoisophthalic acid) which features a (3,6) topological network. Eu-MOF exhibits high structure stability in water, organic solvents and at pH ​= ​1–12. The sensitivity test indicates a linear equation of I0/I ​= ​0.04597∙Ctrp + 0.39164 with limit of detection (LOD) calculated as 0.80 ​μM. The fluorescence quenching mechanism is analyzed based on Stern-Volmer (SV) equation, giving the SV quenching rate constant (KSV) of 4.307 ​× ​104 ​M−1 and the quenching rate constant (Kq) of 2.51 ​× ​108 ​M−1 ​s−1, demonstrating tryptophan (trp) quenching Eu-MOF is a dynamic quenching process. In the selectivity test, trp shows the fluorescence quenching compared to twelve control compounds, and the interferents don't affect trp quenching Eu-MOF. Eu-MOF also exhibits a high durability that the characteristic emission remains stable in five-fluorescence quenching-recovery cycles. Eu-MOF returns very close calculated trp concentrations to the theoretic values and high recoveries in the application tests of human serum, urine and lake water based on the linear equation. The paper-based Eu-MOF sensor displays obvious emission color changes, whose red values (R) reveal a linear equation of R ​= ​−0.54857∙Ctrp ​+ ​188.33, indicating the possibility of the on-site trp detection. Totally, Eu-MOF is a rapid turn-off fluorescence sensor to trp with high sensitivity, selectivity, and durability.