Size-Dependent Accumulation of PEGylated Silane-Coated Magnetic Iron Oxide Nanoparticles in Murine Tumors

Magnetic nanoparticles (MNP) can be used as contrast-enhancing agents to visualize tumors by magnetic resonance imaging (MRI). Here we describe an easy synthesis method of magnetic nanoparticles coated with polyethylene glycol (PEG) and demonstrate size-dependent accumulation in murine tumors following intravenous injection. Biocompatible iron oxide MNPs coated with PEG were prepared by replacing oleic acid with a biocompatible and commercially available silane-PEG to provide an easy and effective method for chemical coating. The colloidal stable PEGylated MNPs were magnetically separated into two distinct size subpopulations of 20 and 40 nm mean diameters with increased phagocytic uptake observed for the 40 nm size range in vitro. MRI detection revealed greater iron accumulation in murine tumors for 40 nm nanoparticles after intravenous injection. The enhanced MRI contrast of the larger MNPs in the tumor may be a combined result of the size-dependent extravasation and capture by macrophages in the tumor, providing important considerations for improved bioimaging approaches.