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

Abstract

In this work, by conjugating a europium complex, 4,4′-bis(1′′,1′′,1′′,2′′,2′′,3′′,3′′-heptafluoro-4′′,6′′-hexanedion-6′′-yl)chlorosulfo-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 (∼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, while that at 410 nm shows no response to the addition of Cu²⁺ ions. Correspondingly, the emission intensity ratio, I₆₁₅/I₄₁₀, 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.