Integrated Eu³⁺ loaded covalent organic framework with smartphone for ratiometric fluorescence detection of...

Developing rapid tetracycline sensing system is of great significance to monitor the illegal addition to drugs and pollution to food and ecosystem. By loading covalent organic frameworks (COFs) with Eu³⁺, a new hybridized material (COF@Eu³⁺) was prepared for tetracycline determination. Based on the Schiff base reaction, the COFs were by synthesized through solvent evaporation in 30 min at room temperature. Thereafter, Eu³⁺ was modified into COFs to develop the COF@Eu³⁺ sensing platform by adsorption and coordination. In presence of tetracycline, tetracycline can displace water molecules and coordinate with Eu³⁺ through the antenna effect. As a result, the red fluorescence of Eu³⁺ was enhanced by tetracycline with green fluorescence of COF as a reference. The developed ratiometric fluorescence sensor exhibits a linear range of 0.1-20 μM for detecting tetracycline with a detection limit of 30 nM. Integrated with a smartphone, the rapid tetracycline detection can be realized in situ, which is potential for high-throughput screening of tetracycline contaminated samples. Furthermore, the COF@Eu³⁺ fluorescence sensor has been successfully applied to the detection of tetracycline in traditional Chinese medicine compound preparation with satisfied recoveries. Therefore, a smartphone-assisted device was successfully developed based on Eu³⁺-functionalized COF, which is an attractive candidate for further applications of fluorescence sensing and visual detection.