Recyclable Magnetic Fluorescent Fe₃O₄@SiO₂ Core–Shell Nanoparticles Decorated with Carbon Dots for Fluoride Ion Removal

Tremendous efforts have been dedicated to developing fluorescent probes with biocompatible and cyclic features. Challenges remain in terms of high toxicity, poor dispersity in aqueous solution, low efficiency, and high detection limit problems. Inspired by the low biotoxicity and high quantum yield of amine-modified carbon dots (NCDs) as well as the reversible binding between metal ions (Mn+ ions) and carbon dots, a fluorescent quenching receptor is created based on the mechanism of nonradiative electron transfer from NCDs to Mn+ ions. This fluorescent quenching receptor is coordinated on a mesoporous superparamagnetic Fe3O4@mSiO2 nanoparticle, which forms a probe structure of Fe3O4@mSiO2-SiCDs@DTPA-Mn+/NCDs. NCDs detach from metal ions and recover their fluorescence when the probe is placed in the environment to be detected. The concentration of fluoride ions (F– ions) in the environment could be determined by the fluorescence intensity of the detached NCDs. This novel nanoscale probe has recyclable performance and can be reused at least 6 times. The minimum detection limit is down to 65 nM with a wide linear response range of 1 to 25 μM. The ion removal capacity could be up to 21.4 mg/g. This nanoscale fluorescent probe can be used for sufficiently high-response F– ion detection and removal of the platform.