Silica-Coated Manganese Oxide Nanoparticles as a Platform for Targeted Magnetic Resonance and Fluorescence Imaging of Cancer Cells

Monodisperse silica-coated manganese oxide nanoparticles (NPs) with a diameter of similar to 35 nm are synthesized and are aminated through silanization. The amine-functionalized core-shell NPs enable the covalent conjugation of a fluorescent dye, Rhodamine B isothiocyanate (RBITC), and folate (FA) onto their surface. The formed Mn3O4@SiO2(RBITC)-FA core-shell nanocomposites are water-dispersible, stable, and biocompatible when the Mn concentration is below 50 mu g mL(-1) as confirmed by a cytotoxicity assay. Relaxivity measurements show that the core-shell NPs have a T-1 relaxivity (r(1)) of 0.50 mM(-1) s(-1) on the 0.5 T scanner and 0.47 mM(-1) s(-1) on the 3.0 T scanner, suggesting the possibility of using the particles as a T-1 contrast agent. Combined flow cytometry, confocal microscopy, and magnetic resonance imaging studies show that the Mn3O4@SiO2(RBITC)-FA nanocomposites can specifically target cancer cells overexpressing FA receptors (FARs). Findings from this study suggest that the silica-coated Mn3O4 core-shell NPs could be used as a platform for bimodal imaging (both magnetic resonance and fluorescence) in various biological systems.