BACKGROUND: At present there is no standard of care for patients with primary central nervous system lymphoma (PCNSL) because of the difficulty in delivering therapeutically effective doses of drugs to the intracellular site of the target PCNSL. Here we report the use of an iron oxide nanoparticle to promote the internalization of a PCNSL targeting antibody by target cells. METHODS: Iron oxide nanoparticles coated with a copolymer of chitosan-grafted polyethylene glycol (NPs) were conjugated with an anti-CD20 single-chain variable fragment-streptavidin fusion protein (FP), and optically activated with Oregon Green 488. The ability of NP-FP to target PCNSL cells was assessed using flow cytometry and the ferrozine assay. Cell internalization of NP-FP was examined by confocal fluorescence microscopy. RESULTS: The antibody-conjugated NPs had a near-neutral zeta potential and remained stable in biological media for more than 1 week, which may minimizes nonspecific cell uptake. The diameter of the NPs was about 70 nm, which is in an optimal range for maximizing cell uptake. The selective binding of these NPs was demonstrated with binding to PCNSL cells 3- to 4-fold higher than binding to control cells. Z-stack imaging by confocal microscopy revealed the NPs were internalized by PCNSL cells. CONCLUSIONS: The high-degree specific binding and cell uptake of NP-FP in PCNSL suggests this NP formulation can be further developed to improve therapy of PCNSL.