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Superparamagnetic Contrast Agents
Published in Michel M. J. Modo, Jeff W. M. Bulte, Molecular and Cellular MR Imaging, 2007
Claire Corot, Marc Port, Irène Guilbert, Philippe Robert, Jean-Sebastien Raynaud, Caroline Robic, Jean-Sebastien Raynaud, Philippe Prigent, Anne Dencausse, Idée Jean-Marc
Oxidation in air is not the only way to transform magnetite (Fe3O4) into maghemite (γFe2O3). Various electron or ion transfers, depending on the pH of the suspension, are involved. Under acidic and anaerobic conditions, surface Fe2+ ions are desorbed as hexa-aqua complexes in solution, whereas, under basic conditions, oxidation of magnetite involves oxidation-reduction of the surface of magnetite. Oxidation of ferrous ions is always correlated with migration of cations through the lattice framework, creating cationic vacancies in order to maintain the charge balance, explaining the structure of maghemite. Consequently, maghemite has a spinel structure inverse to that of magnetite (in maghemite, iron ions are distributed in the octahedral (Oh) and tetrahedral (Td) sites of the spinel structure (Formula 4.1)), but differs from magnetite by the presence of cationic vacancies within the octahedral site. The vacancies ordering scheme is closely related to the sample preparation method and results in symmetry lowering and possibly superstructures. The vacancies can be completely random or partially or totally ordered. It has been shown, essentially from combined infrared (IR) spectroscopy and x-ray diffraction, that vacancy ordering occurs only for particles exceeding 5 nm.19
Targeted Agents for MRI
Published in Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman, Molecular Imaging in Oncology, 2008
As was discussed above, CAs with large magnetic moments induce very efficient relaxation. Superparamagnetic iron oxide (SPIO) nanoparticles were introduced as highly efficient MR CAs. The SPIO magnetic core is typically composed from magnetite, which is an inverse spinel with formula Fe2+O·Fe3+2O3 = Fe3O4. The iron oxide magnetic core is protected by various polymeric coats to ensure biocompatibility of the agent and to prevent formation of aggregates. Depending on the size, the core consists of several thousands of iron atoms and has very high magnetic moment. Because of the large molecular size of SPIO nanoparticles, they have relatively long rotational correlation time, τc, and they act as efficient T1 CAs only at low magnetic fields where the condition ω0 = γB0 = τc−1 is fulfilled. On the other hand, strong local magnetic fields generated by SPIO make them very efficient T2 and T2* CAs with typical T2 relaxivity R2 in the order of 50 to 100 [sec·(mM·Fe)]−1. A single SPIO particle consists of a large amount of iron, which results in several order of magnitude higher relaxivities per CA molecule in comparison to Gd-based agents. Several different SPIO preparations have been tested for MRI applications, including monocrystalline iron oxide nanoparticles (MION), with a core diameter of 4.6 nm and nanoparticles diameter of about 20 nm; ultrasmall SPIO (USPIO), with 3 to 4 nm core and hydrodynamic diameter <25 nm; cross-linked iron oxide (CLIO), classical SPIO such as Feridex (Berlex Laboratories, Wayne, New Jersey, U.S.) with 5- to 6-nm polycrystalline core and dextran coating and ~ 35 nm average diameter (10). Large SPIO particles with polystyrene coating and a diameter of ~ 1 μm are produced by Bangs, Inc. (Fishers, Indiana, U.S.) and are very useful as in vitro cell labeling probes (11).
Superparamagnetic iron oxide nanoparticles (SPIONs) modulate hERG ion channel activity
Published in Nanotoxicology, 2019
Roberta Gualdani, Andrea Guerrini, Elvira Fantechi, Francesco Tadini-Buoninsegni, Maria Rosa Moncelli, Claudio Sangregorio
In conclusion, we investigated the effect of water suspensions of SPIONs characterized by different size, coating, or oxidation state (magnetite or maghemite) of the inorganic core, on the activity of hERG channel. This protein plays a crucial role in the repolarization of cardiac action potential and regulation of the heartbeat and it is therefore an ideal system for preclinical cardiotoxicity testing of new drugs and nanomaterials. Using patch-clamp recordings, we found that Fe3O4 NP suspensions have an inhibitory effect on the hERG current, which depends on the size (the larger the size, the smaller the effect) and on the coating of the magnetic NPs. Conversely, almost no inhibition of the hERG channel was observed when the NPs were converted to the fully oxidized spinel, maghemite.
Folate-molecular encapsulator-tethered biocompatible polymer grafted with magnetic nanoparticles for augmented drug delivery
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Sivaraj Ramasamy, Rex Jeya Rajkumar Sam David, Israel V. M. V. Enoch
Spinel ferrites substituted with elements like Mn2+, Co2+, Ni2+ and Zn2+ provide opportunity to fine-tune the magnetic characteristics of the MNP core depending on the kind of divalent ion [7]. Coating of MNPs with biocompatible carbohydrate polymers like dextran mitigates the toxicity of the MNPs. The induction of reactive oxygen species (ROS) depends on the firmness of the coating agent, its inclination to produce ROS and concentration inside the cells [13–16]. A few dextran-coated MNP formulations have been approved as MRI contrast agents by the FDA and EMA [7]. A raise to a more desirable or better quality of recourse of tumour specific hitting, water-soluble folate conjugates are designed and synthesized as the folate conjugation facilitates the uptake by folate-receptor overexpressed cells [17].
Multifunctional magnetite nanoparticles to enable delivery of siRNA for the potential treatment of Alzheimer’s
Published in Drug Delivery, 2020
Natalia Lopez-Barbosa, Juan G. Garcia, Javier Cifuentes, Lina M. Castro, Felipe Vargas, Carlos Ostos, Gloria P. Cardona-Gomez, Alher Mauricio Hernandez, Juan C. Cruz
XRD measurements were performed prior to and after the silanization of the magnetite nanoparticles. Identified peaks in Figure 1(A) allowed to confirm the effective synthesis of magnetite nanoparticles by both coprecipitation and thermal decomposition techniques, showing a crystalline structure of inverse spinel, which is characteristic of magnetite nanoparticles (Fe3O4) (JCPDS 15-8743). Lanthanum hexaboride (LaB6) was used as a correction factor to obtain the approximate size of the ordered crystalline domains by using Scherrer equation (Equation (1); Hui et al., 2015; Tatarchuk et al., 2017) as follows: