Fluorescein-polyethyleneimine coated gadolinium oxide nanoparticles as T₁ magnetic resonance imaging (MRI)-cell labeling (CL) dual agents

We report the synthesis, characterization and application of highly water-soluble fluorescein-polyethyleneimine (PEI) coated gadolinium oxide (Gd₂O₃) nanoparticles to magnetic resonance imaging (MRI) and cell labeling (CL). The average particle diameter and average hydrodynamic diameter were estimated to be 3.92 and 7.5 nm, respectively. Fluorescein-PEI was prepared from EDC/NHS coupling method. The surface coating was characterized by the FT-IR absorption spectrum and the surface coating amount was estimated to be 22.42 wt% from a TGA analysis, corresponding to 0.65 nm^-2 grafting density. The fluorescein-PEI coated gadolinium oxide nanoparticles showed r₁ and r₂ of 6.76 and 20.27 s^-1mM^-1, respectively, and a strong fluorescence at ∼527 nm. A pronounced positive contrast enhancement was clearly observed in 3 tesla T₁ MR images of a rat with a liver tumor after injection of an aqueous sample solution into a rat tail vein. After treatment of DU145 cells with a sample solution, a strong fluorescence in confocal images was also observed. These two results together confirm the excellent MRI-CL dual functionality of fluorescein-PEI coated gadolinium oxide nanoparticles.