Silica-coated ZnS: Mn nanoparticles were synthesized by coating hydrophobic ZnS: Mn nanoparticles with silica shell through microemulsion. The core-shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core-shell nanoparticle contains single ZnS: Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV-vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS: Mn nanoparticles, the silica-coated ZnS: Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS: Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu2+ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu2+ concentrations as low as 7.3 x 10 (9) mol L (1), thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed. (C) 2009 Elsevier Inc. All rights reserved.