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.