Cooperative Organization in Iron Oxide Multi-Core Nanoparticles Potentiates Their Efficiency as Heating Mediators and MRI Contrast Agents

In the pursuit of optimized magnetic nanostructures for diagnostic and therapeutic applications, the role of nanoparticle architecture has been poorly investigated. In this study, we demonstrate that the internal collective organization of multi-core iron oxide nanoparticles can modulate their magnetic properties in such a way as to critically enhance their hyperthermic efficiency and their MRI <i>T</i>₁ and <i>T</i>₂ contrast effect. Multi-core nanoparticles composed of maghemite cores were synthesized through a polyol approach, and subsequent electrostatic colloidal sorting was used to fractionate the suspensions by size and hence magnetic properties. We obtained stable suspensions of citrate-stabilized nanostructures ranging from single-core 10 nm nanoparticles to multi-core magnetically cooperative 30 nm nanoparticles. Three-dimensional oriented attachment of primary cores results in enhanced magnetic susceptibility and decreased surface disorder compared to individual cores, while preserving a superparamagnetic-like behavior of the multi-core structures and potentiating thermal losses. Exchange coupling in the multi-core nanoparticles modifies the dynamics of the magnetic moment in such a way that <i>both</i> the longitudinal and transverse NMR relaxivities are also enhanced. Long-term MRI detection of tumor cells and their efficient destruction by magnetic hyperthermia can be achieved thanks to a facile and nontoxic cell uptake of these iron oxide nanostructures. This study proves for the first time that cooperative magnetic behavior within highly crystalline iron oxide superparamagnetic multi-core nanoparticles can improve simultaneously therapeutic and diagnosis effectiveness over existing nanostructures, while preserving biocompatibility

Iron Oxide Monocrystalline Nanoflowers for Highly Efficient Magnetic Hyperthermia

Magnetic nanoparticles exhibit a high potential to selectively treat cancer by hyperthermia provided that high heating capacity can be reached. In this work, we report an efficient synthesis of novel structures of magnetic iron oxide. The particles, obtained by applying a modified “polyol” protocol, present a particular shape: they look constituted of smaller grains of approximately 11 nm, assembled in a flower-shaped structure. These nanoflowers, dispersed in water at physiological pH, present particularly interesting magnetic properties and a great capacity of heating. The value of the specific loss power (SLP) of these nanoflowers is 1 order of magnitude higher than the SLP reported for conventional 11 nm single-domain maghemite nanoparticles in the same condition of field exposure