Subsequently, we evaluated fluorescence sensing and selective recognition of JUC-557-nanosheet for anions, including SO 4 2-, CO 3 2-, F -, Cl -, Br -, and I -. Pure JUC-557-nanosheet showed low sensitivity for various anions (Supplementary Fig. ). However, the system of JUC-557-nanosheet combined with Fe 3+ was much more sensitive for specific halide anions, such as F -and I -(Fig. ). The residual fluorescence intensity of JUC-557-nanosheet after adding Fe 3+ (c = 60 µg mL -1 ) was approximate 20%. However, when F -ion was added into this system, the fluorescence of JUC-557-nanosheet with Fe 3+ was remarkably enhanced (up to 38%), which could be attributed to the formation of a stable coordination complex, FeF 6 3-. The quenched fluorescence of JUC-557-nanosheet with Fe 3+ could not be fully recovered because there may be a competitive equilibrium between the cyan group and F -with Fe 3+ . Interestingly, different from the detection of F -, the addition of I -resulted in an even more fluorescence decrease of JUC-557-nanosheet with Fe 3+ (as low as 6%) since I -can be oxidized to I 2 by Fe 3+ ions.