A macrophage specific nanoparticle suitable for magnetic resonance, fluorescence, and magnetic particle imaging

Introduction: Magnetic particle imaging (MPI), introduced in 2005, is a new imaging modality that allows the direct visualization of magnetic particle concentration with high sensitivity and unprecedented high temporal resolution (1). The advantages of MPI could be exploited for a variety of purposes, particularly in real-time cardiac imaging. The successful application of MPI relies heavily on the properties of the superparamagnetic nanoparticles used. It is of eminent importance that the nanocrystalline characteristics of these particles, i.e. crystalline structure, size and magnetic properties, are judiciously chosen and well defined. Recently, we introduced a nanoparticle platform of which the coating was based on high density lipoprotein (HDL) and the core was comprised of an iron oxide nanocrystal (FeO-HDL) (2). In vitro, this platform was demonstrated to exhibit macrophage specificity and in vivo it was successfully employed for macrophage imaging in atherosclerotic plaques of apoE-KO mice using magnetic resonance imaging (MRI), fluorescence imaging and confocal microscopy. In the current study we further modified this platform to make it also suitable for MPI by using 20 nm, highly monodisperse magnetic particles as the core of FeO-HDL. We demonstrate preferential uptake by cultured macrophages with confocal laser scanning microscopy (CLSM), MRI, and magnetic particle spectroscopy (MPS).