Controllable Fabrication of Rare-Earth-Doped Gd₂O₂SO₄@SiO₂ Double-Shell Hollow Spheres for Efficient Upconversion Luminescence and Magnetic Resonance Imaging

Uniform hollow spheres of Yb and Er codoped Gd 2 O 2 SO 4 (noted as Gd 2 O 2 SO 4:Yb,Er) have been developed as novel bifunctional contrast agents for efficient upconversion optical and magnetic resonance imaging (MRI) for the first time. Gd-containing organic precursory spheres were first obtained by a facile hydrothermal process. Owing to the innate hydrophilic nature of the precursory spheres, surface modification with a layer of stable and biocompatible silica could be readily achieved through the Stöber sol–gel method and subsequent calcination. The morphology and thickness of the silica shell can be tailored by adjusting the reaction time. Compared with Gd 2 O 2 SO 4:Yb,Er hollow spheres without silica coating, well-dispersed Gd 2 O 2 SO 4:Yb,Er@SiO 2 double-shell hollow spheres could generate intense upconversion fluorescence, and showed a significant contrast enhancement of T1-weighted MRI both in vitro and in vivo . These gadolinium oxysulfate-based hollow spheres are thus regarded as a new type of potential bimodal optical-MRI contrast agents.