A Single Picture Explains Diversity of Hyperthermia Response of Magnetic Nanoparticles

Progress in the design of nanoscale magnets for localized hyperthermia cancer therapy has been largely driven by trial-and-error approaches, for instance, by changing of the stoichiometry composition, size, and shape of the magnetic entities. So far, widely different and often conflicting heat dissipation results have been reported, particularly as a function of the nanoparticle concentration. Thus, achieving hyperthermia-efficient magnetic ferrofluids remains an outstanding challenge. Here we demonstrate that diverging heat-dissipation patterns found in the literature can be actually described by a single picture accounting for both the intrinsic magnetic features of the particles (anisotropy, magnetization) and experimental conditions (concentration, magnetic field). Importantly, this general magnetic-hyperthermia scenario also predicts a novel non-monotonic concentration dependence with optimum heating features, which we experimentally confirmed in iron oxide nanoparticle ferrofluids by fine-tuning the particle size. Overall, our approach implies a <i>magnetic hyperthermia trilemma</i> that may constitute a simple strategy for development of magnetic nanomaterials for optimal hyperthermia efficiency

Modulation of Magnetic Heating via Dipolar Magnetic Interactions in Monodisperse and Crystalline Iron Oxide Nanoparticles

In the pursuit of controlling the heat exposure mediated by magnetic nanoparticles, we provide new guidelines for tailoring magnetic relaxation processes via dipolar interactions. For this purpose, highly crystalline and monodisperse magnetic iron oxide nanocrystals whose sizes range from 7 to 22 nm were synthesized by thermal decomposition of iron organic precursors in 1-octadecene. The as-synthesized nanoparticles are soft nanomagnets, showing superparamagnetic-like behavior and SAR values which progressively increase with particle size, field frequency, and amplitude up to 3.6 kW/g_Fe. Our data show the influence of media viscosity, particle size, and concentration on dipolar interactions and consequently on the magnetic relaxation processes related to the heat release. Understanding the role of dipolar interactions is of great importance toward the use of iron oxide nanoparticles as efficient hyperthermia mediators

High-Performance Implantable Sensors based on Anisotropic Magnetoresistive La_0.67Sr_0.33MnO₃ for Biomedical Applications

We present the design, fabrication, and characterization of an implantable neural interface based on anisotropic magnetoresistive (AMR) magnetic-field sensors that combine reduced size and high performance at body temperature. The sensors are based on La0.67Sr0.33MnO3 (LSMO) as a ferromagnetic material, whose epitaxial growth has been suitably engineered to get uniaxial anisotropy and large AMR output together with low noise even at low frequencies. The performance of LSMO sensors of different film thickness and at different temperatures close to 37 °C has to be explored to find an optimum sensitivity of ∼400%/T (with typical detectivity values of 2 nT·Hz–1/2 at a frequency of 1 Hz and 0.3 nT·Hz–1/2 at 1 kHz), fitted for the detection of low magnetic signals coming from neural activity. Biocompatibility tests of devices consisting of submillimeter-size LSMO sensors coated by a thin poly(dimethyl siloxane) polymeric layer, both in vitro and in vivo, support their high suitability as implantable detectors of low-frequency biological magnetic signals emerging from heterogeneous electrically active tissues