Triple-Emitting Dumbbell Fluorescent Nanoprobe for Multicolor Detection and Imaging Applications

The combination of different fluorescent species into one nanostructure to develop fluorescent nanoparticles with multiple emission signatures by a single wavelength excitation has become a very popular research area in the field of multiplex bioanalysis, diagnostics, and multicolor imaging. However, these novel hybrids must be elaborately designed to ensure that the unique properties of each component are conveyed, i.e., fluorescent species and nanoparticles, and are maximized without serious interactions with each other. Herein, a first triple-fluorescence dumbbell nanoprobe with large Stokes shift based on incorporating fluorescein isothiocyanate (FITC) and lanthanide complexes onto Au–Fe₃O₄ NPs was synthesized. This hybrid displays well-resolved triple fluorescence emission, with FITC at 515 nm, Tb­(III) complex at 545 nm, and Eu­(III) complex at 616 nm under a single-excitation wavelength and is used for highly selective and sensitive colorimetric detection of Cu²⁺ with a detection limit of 30 nM. Under different Cu²⁺ concentrations, this hybrid exhibited distinguishable multiple colors under UV light, and the color could change in the presence of different concentrations of Cu²⁺. This sensor for ratio/multianalyte microscopic imaging of Cu²⁺ in HeLa cells and BHK cells was also demonstrated. Target molecules, such as folic acid, can be covalently attached to the fluorescent nanoparticle surface to serve as an effective probe for simultaneous multicolor imaging folate receptor-overexpressing HeLa cell lines in vitro