Controlled oxidation and surface modification increase heating capacity of magnetic iron oxide nanoparticles

Abstract

Magnetic iron oxide nanoparticles (MIONs) can generate heat under an alternating magnetic field, enabling a wide range of applications from water treatment to cancer hyperthermia therapy. For most magnetic heating applications, it is crucial to generate a high level of heat with a low dose of MIONs. Current methods to increase the specific absorption rate (SAR) of MIONs include increasing their size and doping iron oxide nanocrystals with other metal elements. Here, we demonstrate that controlled oxidation and surface modification can significantly increase SAR of MIONs. We synthesized MIONs of different core sizes and with different coatings, including phospholipid-PEG and triethylenetetramine (TETA). We oxidized PEG-coated MIONs in a controlled fashion and measured the SAR values of the MIONs under different oxidation states. We found that, with controlled oxidation, the SAR values of 15-nm and 18-nm MIONs increased by ∼1.87 fold after two weeks of oxidation. A similar fold-increase in SAR was achieved for 15-nm MIONs with TETA coating compared with PEG coating. We systematically characterized the physical properties of MIONs and showed that oxidation caused MIONs to transition from magnetite to maghemite, resulting in increased anisotropy constant and SAR values. Our results demonstrate new approaches to significantly increase the heating capacity of MIONs by controlled nanocrystal oxidation and surface modification.

Magnetic Fields and Cancer: Epidemiology, Cellular Biology, and Theranostics

“…Ferrimagnetic glass-ceramic have been successfully used as thermo-seeds for a hyperthermic treatment of carcinoma cells in Sprague-Dawley rats [589], whereas magnetite cationic liposomes where used to generate hyperthermia on local tumors and lung metastases in a mouse model of osteosarcoma [590]. Spinel ferrite nanoparticles were successfully synthesized and used for MHT [591], whereas MIONs (such as crack-free ferrimagnetic maghemite, γ-Fe 2 O 3 ) may be useful for the in situ hyperthermic treatment of cancer [592][593][594][595]. SPIONs have been increasingly studied for their excellent MHT applications [596,597], whereas lanthanum-strontium manganite particles that were embellished with gold nanoparticles were found to be suitable for the treatment of deeper tumors [598].…”

Enhanced Magnetic Hyperthermia of Magnetoferritin through Synthesis at Elevated Temperature

“…Magnetic anisotropy is also a significant parameter that influences the hyperthermic efficiency of MNPs [ 49 ]. With the determined T B value, the anisotropy constant K A of MNPs with no magnetic interactions can be calculated by [ 50 ]. where t 0 is the timescale of the measurement (100 s), τ 0 is the microscopic jump time (10 −9 s), k B is the Boltzmann constant, and V is the volume of MNPs, which can be estimated using the average particle diameter determined via TEM measurements (spherical shape approximation).…”

Redox phase transformations in magnetite nanoparticles: impact on their composition, structure and biomedical applications

“…At room temperature, magnetite exhibits a spin-polarized conductivity due to the rapid hopping of the additional electron every two Oh sites [11] (see section 2). However, as a result of electronic transitions due to overlapping Fe-3d orbitals [120,121], there is a weak electron localization into a polaron responsible for an intervalence charge transfer band in the near infrared radiation (NIR) region (0.6-1 eV), which has been exploited by some authors to monitor the conversion between magnetite and maghemite [25,120,122]. For example, by following the absorbance of a NP suspension, Jung and Schimpf [122] showed that a colloid of maghemite NPs can be reduced to magnetite by using ethanol as a sacrificial reductant during UV irradiation (figure 3(b)).…”

“…The magnetite lattice can accommodate a full range of stoichiometries (Fe 3−x O 4 ) between stoichiometric magnetite (x = 0) and maghemite (x = 0.33) and it has been demonstrated that the physicochemical response behind most applications depends on the Fe 2+ concentration. For example, the contaminant reduction rates can change several orders of magnitude due to variations in the amount of Fe 2+ [24], whereas the magnetic properties and the heating efficiency of the NPs are strongly modulated by their oxidation degree [25]. While many applications rely on a precise control of the iron oxide stoichiometry, it is known that magnetite NPs transform into maghemite in a topotactic (i.e.…”