One-pot fabrication of polymer nanoparticle-based chemosensors for Cu2+ detection in aqueous media

Cupric pollution is a global problem, and the development of stable and sensitive fluorescent probes for cupric ions in the water phase has long been sought. In the present study, we report on the fabrication of core–shell nanoparticle-based fluorescent chemosensors for Cu2+ detection in aqueous media. The core–shell nanoparticle sensor was prepared by a facile one-pot miniemulsion polymerization, in which the fluorescent dye (4-methamino-9-allyl-1,8-naphthalimide, MANI) was covalently incorporated into particle core and the Cu2+ ligand i.e. Vinylbenzylcyclam (VBC), chemically linked onto the surface. The cyclam-functionalized fluorescent polymeric nanoparticles exhibit a high affinity for Cu2+ ions in aqueous media. Upon the addition of Cu2+, the fluorescent emission of the MANI dye in nanoparticles can be quenched on the basis of intraparticle fluorescence resonance energy transfer (FRET) from the dye in the hydrophobic PMMA core to the Cu2+–cyclam complexes on the nanoparticle surface, and the nanoparticle sensor can selectively detect the Cu2+ in water with the detection limit of 500 nM. The observed FRET efficiencies (31.6–73.4%), as well as the distance (r) between MANI (donor) and Cu2+–cyclam complexes (acceptor), were also determined. No interference was observed from other metal ions, making it a highly sensitive and selective Cu2+ probe. Moreover, the nanoparticle-based fluorescent sensor was applicable in a relatively wide pH range (pH 4–10) in water and it exhibited excellent long-term photostability for Cu2+ detection (>45 days) in aqueous media; thus, this approach may provide a new strategy for ratiometric detection of analytes in environmental and biological applications.