Preparation of europium complex-conjugated carbon dots for ratiometric fluorescence detection of copper(II) ions

In this work, by conjugating a europium complex, 4,4'-bis(1 '',1 '',1 '',2 '',2 '',3 '',3 ''-heptafluoro-4 '',6 ''-hexanedion-6 ''-ypchlorosulfo-o-terphenyl-Eu3+ (BHHCT-Eu3+), onto the surface of carbon dots (C-dots), a new type of dual-fluorophore nanoparticle, C-dots-BHHCT-Eu3+, has been successfully prepared for the ratiometric fluorescence detection of Cu2+ ions in aqueous media. The results of transmission electron microscopy (TEM) and fluorescence spectroscopy characterization indicate that the nanoparticles are monodisperse, spherical and uniform in size (similar to 8.6 nm in diameter), and have stable and well-resolved dual-wavelength emission properties. Under excitation at 337 nm, the composite nanoparticles of C-dots-BHHCT-Eu3+ exhibit two emission peaks at 410 nm and 615 nm, respectively. Upon the addition of Cu2+ ions, the emission intensity of the nanoparticles at 615 nm is significantly decreased, white that at 410 nm shows no response to the addition of Cu2+ ions. Correspondingly, the emission intensity ratio, /(615)//(410), shows a good linearity against the concentration of Cu2+ ions. In addition, the investigation results of fluorescence responses of the nanoparticles to different metal ions reveal that the fluorescence response of C-dots-BHHCT-Eu3+ to Cu2+ ions is highly specific without interference from other metal ions. All of the results suggest that the new dual-fluorophore composite nanoparticles could be used as a ratiometric fluorescence probe for the detection of Cu2+ ions in aqueous media with high selectivity and sensitivity.