Fluorescent and paramagnetic core–shell hybrid nanoparticles for bi-modal magnetic resonance/luminescence imaging

Abstract

Well calibrated core–shell multifunctional nanoparticles for biomedical applications were synthesized by a multistep soft chemistry route. The core is composed of Gd(OH)CO₃·H₂O spheres prepared via a urea-based homogeneous precipitation technique, while the shell is a homogeneous thin silica layer embedded with the fluorescent dye rhodamine B (RhB) prepared via a modified Stöber process. The hybrid core–shell nanoparticles show a paramagnetic behavior with a specific saturation magnetization of 2.8 emu g⁻¹. The nuclear magnetic resonance relaxation measurements reveal that these systems could be used as T₁ and T₂ magnetic resonance imaging (MRI) contrast agents. Also, the resulting core–shell nanoparticles are fluorescent due to the presence of RhB entrapped inside the silica shell. When incubated with the human cervical carcinoma (HeLa) cells the core–shell composite particles exhibit bright intracellular fluorescence, indicating their capability for optical imaging in biology. Furthermore, the incorporation of organic dyes inside the silica matrix yields outstanding advantages such as significantly improved photostability of the dye and reduced cytotoxicity due to the protection of biocompatible silica shell. These features demonstrate that the magnetofluorescent core–shell nanoparticles prepared in our work have the potential to serve as a versatile imaging tool for smart detection or diagnosis in future biomedical engineering.