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Carbon Dots and Terbium Co-Enhanced Fluorescence of Europium Nanoparticles for Cell Imaging.

Eu(III) and Tb(III) ions were doped into carbon dots (C dots) for the preparation of C:EuTb nanoparticles (C:EuTb NPs) via one-pot synthesis. Because of the dual energy transfer effects from C dots and Tb(III) ion to Eu(III) ion, the fluorescence of Eu(III) in C:EuTb NPs is enhanced 336.8-fold without any antenna molecules. The intense fluorescence of C:EuTb NPs is not easily quenched in aqueous solutions due to the insertion of Eu(III) ions into C dots, which reduces the quenching from water molecules, overcoming the weakness of fluorescence quenching of lanthanide materials in water. Not only in aqueous solution, solid C:EuTb NPs also present strong fluorescence because of the doped structure. The cytotoxicity of C:EuTb NPs is determined by an MTT (thiazolyl blue) assay for human breast adenocarcinoma cell line (MCF-7) cells. C:EuTb NPs show excellent biological safety; the viability of MCF-7 is more than 90% even at a concentration of 1250 μg·mL-1 of C:EuTb NPs. MCF-7 cells stained with C:EuTb NPs display distinct red fluorescence in the fluorescent field of microscope. C:EuTb NPs are promising to be used as a red coloring agent for biological observations.