A red-emitting Europium(III) complex as a luminescent probe with large Stokes shift for the sequential determination of Cu and biothiols in real samples.

In this work, a novel Eu-DTPA-bis(AMC) complex with red luminescence was designed and synthesized for sequential detection of Cu and biothiols (Cys/Hcy/GSH) based on the displacement strategy with the good selectivity, high sensitivity, and large Stokes shift (288 nm). The possible detection mechanism was verified by UV-vis, the high-resolution mass spectrometry, and the fluorescence decay curve. The experimental parameters, including the solution pH, the incubation time, the concentration ratio of Eu-DTPA-bis(AMC) to Cu and biothiols concentration, were optimized. Under the optimal conditions, it shows a good linear relationship between the concentration (0-10 μM) of Cu and the fluorescence intensity of Eu-DTPA-bis(AMC), with a low detection limit of 0.065 μM. The linear range and the limit of detection of the Eu-DTPA-bis(AMC)/Cu system for Cys/Hcy/GSH were 2.5-22.5/5-45/5-50 μM and 0.11/0.07/0.05 μM, respectively. Surprisingly, the high or low concentration of Eu-DTPA-bis(AMC)/Cu can significantly affect the selectivity of the sensing system to biothiols (Cys/GSH/Hcy). When the concentration of the Eu-DTPA-bis(AMC)/Cu system is 10.0 μΜ, it could recognize biothiols (Cys/GSH/Hcy) from other substances, but when the concentration is as low as 3.3 μM, it could further specifically distinguished Cys from Hcy/GSH. Owing to the high anti-interference characteristics, accuracy and specificity, the sensing system was well applied to the cascade detection of Cu in actual environmental samples and Cys in biological and food samples, including FBS, urine, milk, beverage, fresh juice with the satisfactory recoveries from 96.20 to 106.80 %.