Preparation of europium-quantum dots and europium-fluorescein composite nanoparticles available for ratiometric luminescent detection of metal ions

The silica-encapsulated luminescent lanthanide nanoparticles have been developed for the selective tagging of a wide range of important targets in recent years, however, they are mainly limited to europium and terbium compounds. In this work, two types of europium-containing dual-luminophore silica nanoparticles, silica-encapsulated CdTe quantum dots (CdTe QDs)-BHHCT-Eu3+ complex nanoparticles and BHHCT-Eu3+ surface-bound silica-encapsulated fluorescein isothiocyanate (FITC) nanoparticles (BHHCT: 4, 4'-bis(1'', 1'', 1'', 2'', 2'', 3'', 3''-heptafluoro-4'', 6''-hexanedion-6''-yl)chlorosulfo-o-terphenyl), were successfully prepared using a water-in-oil (W/O) reverse microemulsion method. The results of transmission electron microscopy and luminescence spectroscopy characterizations indicate that the two types of nanoparticles are all monodisperse, spherical and uniform in size (∼50 nm in diameter), and have well-resolved and stable dual luminescence emission properties. The CdTe QDs-BHHCT-Eu3+ nanoparticles can be excited at 365 nm to give dual-emission peaks at 535 and 610 nm, and the FITC-BHHCT-Eu3+ nanoparticles can be excited at 335 nm to give dual-emission peaks at 515 and 610 nm. The luminescence response investigations of the nanoparticles to different metal ions indicate that the new nanoparticles can be used as ratiometric luminescent sensing probes for the selective detection of Cu2+ and Fe2+ ions, respectively. The performance of the nanoparticle probe for metal ion detection was investigated.