Abstract
AbstractThe structural, microstructural, and magnetic properties of ~5‐nm‐sized Co0.6Zn0.4Fe2 − xGdxO4 nanoparticles were investigated in order to evaluate their capability to enhance the magnetic resonance imaging contrast as high magnetization agents. A focus was made on the solubility of Gd3+ cations within the spinel lattice. By coupling X‐ray diffraction to X‐ray fluorescence spectroscopy, we demonstrated that only a limited fraction of Gd3+ can substitute Fe3+ ions into the whole crystal structure and does not exceed 6 at.‐%. At this concentration, the room temperature (27°C) saturation magnetizations of the prepared superparamagnetic nanocrystals were found to be close to 80 emu g−1. Coating these nanoparticles with hydrophilic dopamine ligands leads to the formation of ~50‐nm‐sized clusters in water. As a consequence, relatively high r2/r1 ratios of transverse to longitudinal proton relaxivities and high r2 values were measured in the resulting colloids at physiological temperature (37°C) for an applied magnetic field of 1.41 T: 33 and 188 mM−1 sec−1, respectively, for the richest system in gadolinium. Moreover, after incubation with healthy human model cells (fibroblasts) at doses as high as 10 μg mL−1, they induce neither cellular death nor acute cellular damage making the engineered probes particularly valuable for negative magnetic resonance imaging contrasting.
Highlights
Superparamagnetic iron oxide nanoparticles (SPIONs) are largely used as negative contrast agents for magnetic resonance imaging (MRI), because of their ability to shorten the longitudinal T1 and transversal T2 relaxation times of the nuclear magnetic moment of water protons
The first one is called the “motional averaging regime” (MAR), for which the protons of freely diffusing water molecules surrounding the particle explore all the possible values of magnetic dipolar field created by the SPIONs
The r2 relaxivity can be expressed as follows, where equation 1a is related to the MAR and equation 1b to the static dephasing regime” (SDR): r2
Summary
Superparamagnetic iron oxide nanoparticles (SPIONs) are largely used as negative contrast agents for magnetic resonance imaging (MRI), because of their ability to shorten the longitudinal T1 and transversal T2 relaxation times of the nuclear magnetic moment of water protons. Representative micrographs showed roughly spherical particles, slightly agglomerated, with an average size ranging between 5 and 6 nm (Fig. 4), suggesting that the produced NPs are consistent with single crystals, interacting mutually magnetically.
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