From Core–Shell FeO/Fe₃O₄ to Magnetite Nanocubes: Enhancing Magnetic Hyperthermia and Imaging Performance by Thermal Annealing

Abstract

We report the synthesis of mostly magnetite nanocubes (NCs) in the size range of 16−23 nm starting from FeO/Fe 3 O 4 core−shell NCs and employing a thermal decomposition method, followed by thermal treatment. To induce the phase transformation, the as-prepared NCs were thermally annealed either directly in an organic solvent before their transfer into water or by a thermal process in an aqueous solution after coating the NCs with an amphiphilic polymer shell to render them soluble in water. The effects of NCs' size and type of post-synthesis annealing on improving their magnetic properties were investigated. The specific absorption rate (SAR) values, which measure the magnetic hyperthermia heating efficiency, were compared directly in water or in a viscous medium of glycerol/water mixtures to mimic the intratumoral dense environment. Among all samples, the 20 nm NCs annealed in organic solvent show the best heating capabilities. The 24 nm NCs exposed to the water annealing process are also able to achieve very high SAR values. Remarkably, all NC samples subjected to annealing exhibit heating efficiency values which are negligibly affected by the viscous media, thus demonstrating their unique SAR performance in a viscous-independent manner. For 20 nm NCs, a threefold higher magnetic particle imaging signal compared to the commercial tracer VivoTrax, and, at the same time, good magnetic resonance imaging contrast were measured.

Kinetics of spontaneous phase transitions from wüstite to magnetite in superparamagnetic core–shell nanocubes of iron oxides

“…The presence of wüstite, magnetite, and goethite was also confirmed by Mössbauer spectroscopy by measurements taken on a freshly prepared sample and published in our previous paper in collaboration. 19 The measurement also detected a paramagnetic FeOOH phase, which was not revealed by XRD, probably due to the amorphous character of this phase. The Mössbauer measurement took six weeks because of the age of the γ radiation source.…”

“…Iron oleate and 23 nm iron oxide NPs were synthesized by the protocols we published recently. 19 Briefly, for the preparation of 23 nm core–shell FeO/Fe 3 O 4 nanocubes (NCs), 2.5 mmol iron oleate, 1 mmol sodium oleate, 1 mmol oleic acid, 6 g of n -tetracosane, and 3 ml of 1-octadecene were mixed in a 50 mL round bottom flask equipped with a magnetic stirrer and a 20 cm condenser. The solution was degassed at 100 °C for 45 minutes under vigorous stirring (1100 rpm).…”

“…16 As such, it then usually goes through post-synthetic annealing to reach the more stable magnetite. 17–19 Previously, the wüstite–magnetite core–shell structure of iron oxide NPs was described. 18,20,21 The related oxidation process was, among others, followed by XRD and TEM techniques on NPs of various sizes and shapes.…”

Smart Magnetic Nanocarriers for Codelivery of Nitric Oxide and Doxorubicin for Enhanced Apoptosis in Cancer Cells

“…The observed higher number average diameter by DLS than TEM could be ascribed to the associated hydrated organic layer on the surface of the particles. 47 , 48 Moreover, the polydispersity in size (d) and particle aggregation will lead to higher average hydrodynamic diameter as DLS is weighted toward large sizes (d 6 dependence of the scattering intensity on particle size). Further, the colloidal stability of SNO-Cy-CMNPs was investigated by monitoring the changes in the hydrodynamic diameter, light scattering intensity, and absorbance with time ( Figure S1a–c , Supporting Information).…”