Correlating Magnetic Hyperthermia and Magnetic Resonance Imaging Contrast Performance of Cubic Iron Oxide Nanoparticles with Crystal Structural Integrity

Abstract

Magnetic iron oxide nanoparticles have multiple biomedical applications in AC-field hyperthermia and magnetic resonance imaging (MRI) contrast enhancement. Here, two cubic particle suspensions are analyzed in detail, one suspension displayed strong magnetic heating and MRI contrast efficacies, while the other responded weakly. This is despite them having almost identical size, morphology, and colloidal dispersion. Aberration-corrected scanning transmission electron microscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy analysis confirmed that the spinel phase Fe 3 O 4 was present in both samples and identified prominent crystal lattice defects for the weakly responding one. These are interpreted as frustrating the orientation of the moment within the cubic crystals. The relationship between crystal integrity and the moment magnitude and dynamics is elucidated for the case of fully dispersed single nanocubes, and its connection with the emergent hyperthermia and MRI contrast responses is established.

Optimal sizes of iron oxide nanoflowers for magnetic hyperthermia depend on the alternating magnetic field conditions

“…Our results follow the report of Levy et al, as well as the recent study of Shingte et al, which clearly demonstrate that lattice defects affect the magnetic moment magnitude and dynamics, resulting in lower magnetization and lower magneto-crystalline energy both for spherical and cubic morphologies. 38,71 In addition, we notice that the remnant magnetization Mr is negligible for batches NF1-6, confirming pure superparamagnetic behavior of the IONPs from 11.8 to 28.7 nm at room temperature as shown in the inset of Figure 3 (a-c). On the opposite, sample NF7 of 29.3 nm diameter shows slight opening of the magnetization curve into a hysteresis loop characterized by a Mr of 81 kA•m -1 at 293 K and zero applied field.…”

Modulation of hyperthermic and relaxometric responses of magnetic iron oxide nanoparticles through ligand exchange provides design criteria for dual-functionality

“…Rinaldi and co-workers have shown reproducibility for the Fe(oleate) system in docosane, 43 a precursor that is difficult to provide reproducibly. 34 To the best of our knowledge, ours is the first reproducibility study reported for the key OA/OAm/Fe(acac) 3 system, a stable, readily available precursor. This advance was key for the analysis into the effects of MNP concentration, surface ligands and suspending medium that follows, as multiple batches were required.…”

“…Simultaneous optimisation of the SAR and relaxivity of MNP suspensions is critical for the development of multi-functional agents, and can provide insights into how moment dynamics determines both properties. 33,34 However this approach has not been reported for spherical MNPs.…”

Effect of Hollow Structures on T1 and T2 Relaxivities and Their Application in Accurate Tumor Imaging

“…Magnetic nanoparticles (MNPs) have been widely used as magnetic resonance imaging (MRI) contrast agents (CAs) to improve the sensitivity and accuracy in lesion detection. − MNPs accelerate both longitudinal ( T 1 ) and transverse ( T 2 ) relaxation processes of protons and fulfill T 1 / T 2 contrast. − The contrasts of MNPs are highly dependent on their crystal structures, which determine their sensitivity and accuracy in MRI contrast imaging . In the classical model, inner-sphere, second-sphere, and outer-sphere regions are classified to investigate the effect of MNPs on protons. , The inner-sphere region involves the direct interaction between protons and MNPs and dominates T 1 contrast. , The Solomon–Bloembergen–Morgan (SBM) theory reveals that the T 1 contrast is the result of energy loss of spin between protons and magnetic ions through dipole–dipole interactions. , T 1 contrasts of traditional paramagnetic compounds are mainly dependent on the coordination number of water ( q ), proton residence lifetime, molecular tumbling time (τ R ), and electronic relaxation time (τ s ). − Compared to paramagnetic compounds, the chemical exchange only occurs between protons and magnetic ions on the surface of MNPs. , For a specific MNP, the q and τ s values of magnetic ions are constant .…”