NMR relaxivity of coated and non-coated size-sorted maghemite nanoparticles

Angular orientation between the cores of iron oxide nanoclusters controls their magneto-optical properties and magnetic heating functions

Oriented attachment of nanobricks into hierarchical multi-scale structures such as inorganic nanoclusters is one of the crystallization mechanisms that has revolutionized the field of nano and materials science. Herein, we show that the mosaicity, which measures the misalignment of crystal plane orientation between the nanobricks, governs their magneto-optical properties as well as the magnetic heating functions of iron oxide nanoclusters. Thanks to high-temperature and time-resolved millifluidic, we were able to isolate and characterize (structure, properties, function) the different intermediates involved in the diverse steps of the nanocluster's formation, to propose a detailed dynamical mechanism of their formation and establish a clear correlation between changes in mosaicity at the nanoscale and their resulting physical properties. Finally, we demonstrate that their magneto-optical properties can be described using simple molecular theories.

Coating Effect on the 1H-NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles

We present a ¹H Nuclear Magnetic Resonance (NMR) relaxometry experimental investigation of two series of magnetic nanoparticles, constituted of a maghemite core with a mean diameter d_TEM = 17 ± 2.5 nm and 8 ± 0.4 nm, respectively, and coated with four different negative polyelectrolytes. A full structural, morpho-dimensional and magnetic characterization was performed by means of Transmission Electron Microscopy, Atomic Force Microscopy and DC magnetometry. The magnetization curves showed that the investigated nanoparticles displayed a different approach to the saturation depending on the coatings, the less steep ones being those of the two samples coated with P(MAA-stat-MAPEG), suggesting the possibility of slightly different local magnetic disorders induced by the presence of the various polyelectrolytes on the particles’ surface. For each series, ¹H NMR relaxivities were found to depend very slightly on the surface coating. We observed a higher transverse nuclear relaxivity, r₂, at all investigated frequencies (10 kHz ≤ ν_L ≤ 60 MHz) for the larger diameter series, and a very different frequency behavior for the longitudinal nuclear relaxivity, r₁, between the two series. In particular, the first one (d_TEM = 17 nm) displayed an anomalous increase of r₁ toward the lowest frequencies, possibly due to high magnetic anisotropy together with spin disorder effects. The other series (d_TEM = 8 nm) displayed a r₁ vs. ν_L behavior that can be described by the Roch’s heuristic model. The fitting procedure provided the distance of the minimum approach and the value of the Néel reversal time (τ ≈ 3.5 ÷ 3.9·10⁻⁹ s) at room temperature, confirming the superparamagnetic nature of these compounds.

Biological Fate of Magnetic Protein-Specific Molecularly Imprinted Polymers: Toxicity and Degradation

Magnetic nanoparticles coated with protein-specific molecularly imprinted polymers (MIPs) are receiving increasing attention thanks to their binding abilities, robustness, and easy synthesis compared to their natural analogues also able to target proteins, such as antibodies or aptamers. Acting as tailor-made recognition systems, protein-specific MIPs can be used in many in vivo nanomedicine applications, such as targeted drug delivery, biosensing, and tissue engineering. Nonetheless, studies on their biocompatibility and long-term fate in biological environments are almost nonexistent, although these questions have to be addressed before considering clinical applications. To alleviate this lack of knowledge, we propose here to monitor the effect of a protein-specific MIP coating on the toxicity and biodegradation of magnetic iron oxide nanoparticles, both in a minimal aqueous degradation medium and in a model of cartilage tissue formed by differentiated human mesenchymal stem cells. Degradation of iron oxide nanoparticles with or without the polymer coating was monitored for a month by following their magnetic properties using vibrating sample magnetometry and their morphology by transmission electron microscopy. We showed that the MIP coating of magnetic iron oxide nanoparticles does not affect their biocompatibility or internalization inside cells. Remarkably, the imprinted polymer coating does not hinder the magnetic particle degradation but seems to slow it down, although this effect is more visible when degradation occurs in the buffer medium than in cells. Hence, the results presented in this paper are really encouraging and open up the way to future applications of MIP-coated nanoparticles into the clinic.