Encapsulation of Dual‐Emitting Fluorescent Magnetic Nanoprobe in Metal‐Organic Frameworks for Ultrasensitive Ratiometric Detection of Cu²⁺

An effective dual‐emission fluorescent metal‐organic framework (MOF)‐based nanoprobe has been established for ultrasensitive and rapid ratiometric detection of Cu 2+ . Such a nanoprobe was prepared by encapsulating fluorescein isothiocyanate (FITC), and Eu(III) complex‐functionalized Fe 3 O 4 into the zeolitic imidazolate framework material (ZIF‐8). In this nanoprobe, FITC was used as a reference signal, thus improving the influence of external uncertainties. The Eu‐complex signal could be quenched after adding an amount of Cu 2+ . The ZIF‐8 could enrich the target analytes, which can amplify the fluorescence signal due to the good adsorption properties of the ZIF‐8. Based on above structural and compositional features, the detection limit of the nanoprobe is 0.1 n m for Cu 2+ , almost 2×10 4 times lower than the maximum allowable amount of Cu 2+ in drinking water, which constructed a platform for effective detection of Cu 2+ . Using the nanoprobe to detect Cu 2+ in aqueous solution is rapid and the probe still remained stable. Additionally, this sensor for the ratiometric fluorescence imaging of copper ions was also certified in real samples and live cells.