Sequential Growth of NaYF4:Yb/Er@NaGdF4 Nanodumbbells for Dual-Modality Fluorescence and Magnetic Resonance Imaging

Upconversional core–shell nanostructures have gained considerable attention due to their distinct enhanced fluorescence efficiency, multifunctionality, and specific applications. Recently, we have developed a sequential growth process to fabricate unique upconversion core–shell nanoparticles. Time evolution of morphology for the NaYF4:Yb/Er@NaGdF4 nanodumbbells has been extensively investigated. An Ostwald ripening growth mechanism has been proposed to illustrate the formation of NaYF4:Yb/Er@NaGdF4 nanodumbbells. The hydrophilic NaYF4:Yb/Er@NaGdF4 core–shell nanodumbbells exhibited strong upconversion fluorescence and showed higher magnetic resonance longitudinal relaxivity (r 1 = 7.81 mM–1 s–1) than commercial contrast agents (Gd-DTPA). NaYF4:Yb/Er@NaGdF4 nanodumbbells can serve as good candidates for high efficiency fluorescence and magnetic resonance imaging.