LARTIGUE ET AL. VOL. 6 ’ NO. 3 ’ 2665–2678 ’ 2012 www.acsnano.org 2665 February 10, 2012 C 2012 American Chemical Society Nanomagnetic Sensing of Blood Plasma Protein Interactions with Iron Oxide Nanoparticles: Impact on Macrophage Uptake Le ´ naic Lartigue, † Claire Wilhelm, † Jacques Servais, † Ce ´cile Factor, ‡ Anne Dencausse, ‡ Jean-Claude Bacri, † Nathalie Luciani, † and Florence Gazeau †, * † Laboratoire Matière et Systèmes Complexes (MSC), UMR 7057 CNRS/Université Paris ; Diderot, PRES Sorbonne Paris Cité, 75205 Paris cedex 13, France and ‡ GUERBET, BP57400, 95943 Roissy CdG Cedex, France U nderstanding the interactions of nanomaterials with the biological en- vironment has crucial implications for both the efficacy of nanomedicines and safety issues in nanotechnology. After en- tering into the bloodstream, nanoparticles interact with biomolecules forming a “bio- nano interface”. At this interface a protein corona results from a dynamic exchange with biomolecules, influencing both the surface state and the local organization of nanoparticles. 1À4 Therefore what the cells “see and process” are no longer the initially engineered nanoparticles, but the dynamic biomoleculeÀnanoparticle complexes which are formed in vivo. 5 The biodistribution and fate of nanoparticles in the organism will significantly depend on their early interac- tions with plasma proteins. 6 Among the variety of nanoparticle func- tionalities, magnetic properties paved the way for various diagnostic and therapeutic applications such as magnetic resonance imaging (MRI), magnetic targeting, magne- tically induced hyperthermia, triggered drug release or magnetic control of cell migration and signaling. 7 Remarkably, all these applications rely on the on-command actuation of nanoparticles by different mag- netic stimuli applied at a distance and can be combined together to design theranos- tic nanoplatforms. 8,9 However, for most of the magnetic nanoparticles, the relatively poor control of their interactions with blood constituents remains a challenging obstacle toward their efficient targeting to specific organs or cells. The primary target of such nanoparticles are macrophages, which can be detected and tracked by MRI, allowing the monitoring of their recruitment into inflamed tissues such as atherosclerotic plaques, adipose tissue, brain ischemia, or tumors. 10À13 Macrophage imaging in var- ious diseases like, for example, the metabolic syndrome, atherosclerosis, stroke, multiple sclerosis, Alzheimer disease, or cancer is one of the most promising goals sought by nano- medicine, using superparamagnetic iron oxide nanoparticles as in vivo MRI markers. 14 * Address correspondence to florence.gazeau@univ-paris-diderot.fr. Received for review January 5, 2012 and accepted February 10, 2012. Published online 10.1021/nn300060u ABSTRACT One of the first biointeractions of magnetic nanoparticles with living systems is characterized by nano- particleÀprotein complex formation. The proteins dynami- cally encompass the particles in the protein corona. Here we propose a method based on nanomagnetism that allows a speci fic in situ monitoring of interactions between iron oxide nanoparticles and blood plasma. Tracking the nanoparticle orientation through their optical birefringence signal induced by an external magnetic field provides a quantitative real-time detection of protein corona at the surface of nanoparticles and assesses eventual onset of particle aggregation. Since some of the plasma proteins may cause particle aggregation, we use magnetic fractionation to separate the nanoparticle clusters (induced by “destabilizing proteins”) from well-dispersed nanoparticles, which remain isolated due to a stabilizing corona involving other di fferent types of proteins. Our study shows that the “biological identity” (obtained after the particles have interacted with proteins) and aggregation state (clustered versus isolated) of nanoparticles depend not only on their initial surface coating, but also on the concentration of plasma in the suspension. Low plasma concentrations (which are generally used in vitro) lead to di fferent protein/nanoparticle complexes than pure plasma, which reflects the in vivo conditions. As a consequence, by mimicking in vivo conditions, we show that macrophages can perceive several di fferent populations of nanoparticle/protein complexes (di ffering in physical state and in nature of associated proteins) and uptake them to a different extent. When extrapolated to what would happen in vivo, our results suggest a range of cell responses to a variety of nanoparticle/ protein complexes which circulate in the body, thereby impacting their tissue distribution and their efficiency and safety for diagnostic and therapeutic use. KEYWORDS: bionanointeractions . nanomagnetism . nanomedicine . superparamagnetic iron oxide nanoparticles . blood plasma . mononuclear phagocyte system ARTICLE