Europium-Doped TiO₂ Hollow Nanoshells: Two-Photon Imaging of Cell Binding

A simple scalable method to fabricate luminescent monodisperse 200 nm europium doped hollow TiO(2) nanoshell particles is reported. Fluorophore reporter, Eu(3+) ions, are incorporated directly in the NS matrix, leaving the surface free for functionalization and the core free for payload encapsulation. Amine functionalized polystyrene beads were used as templates, and the porous walls of europium doped titania nanoshells were synthesized using titanium(IV) t-butoxide and europium(III) nitrate as reactants. X-ray diffraction analysis identified anatase as the predominant titania phase of the rigid nanoshell wall structure, and photoluminescence spectra showed that the Eu(III) doped TiO(2) nanoshells exhibited a red emission at 617 nm due to an atomic f-f transition. Nanoshell interactions with HeLa cervical cancer cells in vitro were visualized using two-photon microscopy of the Eu(III) emission, and studied using a luminescence ratio analysis to assess nanoshell adhesion and endocytosis.