Multicore Magnetic Fe₃O₄@C Beads With Enhanced Magnetic Response for MRI in Brain Biomedical Applications

In this paper, spherical core@shell (multi-Fe ₃ O ₄ @C) magnetic beads (DMB ~ 100 nm), composed of several single cores of magnetite nanoparticles (MNPs) (Dsingle-core ~ 15 nm) surrounded by a wide carbon shell (δ ~ 20 nm), have been synthesized by a solvothermal procedure in organic solvent that provides good control over size, shape, and crystallinity of the iron oxide nanostructures. Large colloidal stability and good biocompatibility are ensured by the carbon shell, whose thickness can be tuned by the synthesis conditions, and endow the NP with robust stability under extreme physicochemical conditions (acid and base media, or high temperatures and pressures). In vitro testing with rat mesenchymal cells shows high stability and high labeling capacities combined with poly-L-lysine for further cell tracking applications. The so-obtained multi-core MNPs, present: 1) superparamagnetic behavior with a saturation magnetization around 70 emu/g Fe ₃ O ₄ at 25 kOe and room temperature and 2) negligible heating by magnetic hyperthermia procedure and an enhanced magnetic resonance imaging (MRI) response. The simultaneous fulfillment of all the previously listed properties makes these multiFe ₃ O ₄ @C NPs ideal candidates for MRI brain multifunctional applications, where deleterious heating of tissues is a major restriction that ends up in the rejection of, otherwise, magnetically and chemically well-engineered NPs.