MPS and ACS with an atomic magnetometer

We show that a single atomic magnetometer in a magnetically unshielded environment can be used to perform magnetic particle spectroscopy (MPS) and AC susceptometry (ACS) on liquid-suspended magnetic nanoparticles. We demonstrate methods allowing a simultaneous recording of M(H) and dM/dH(H) dependences of samples containing down to 1 μg of iron. Our results pave the way towards an atomic magnetometer based MPI scanner

Study of magnetic relaxation dynamics in soft matter nanoparticle composite systems

Die vorliegende Arbeit behandelt magnetische Relaxationsphänomene von Eisenoxid-Nanopartikeln, eingebracht in verschiedene viskose und viskoelastische Kompositmaterialien, und deren Reaktion auf externe Stimuli. Die Kombination magnetischer Nanopartikel und verformbaren Matrixmaterials eröffnet eine Vielzahl möglicher Anwendungen, von denen jede eigene Anforderungen an die Reaktion des Komposits auf seine Umgebung hat, welche durch die Magnetisierungsdynamik der eingebetteten Nanopartikel bestimmt wird. Daher liegt das Hauptaugenmerk auf dem Einfluss der Nanostruktur des umgebenden Mediums und der Partikel-Matrix-Wechselwirkung auf das dynamische Magnetisierungsverhalten der Partikel im Soft-Matter Komposit. Um einen Vergleich dieser Größen auf verschiedenen Längen- und Zeitskalen zu ermöglichen, wurde AC-Suszeptometrie (ACS) ergänzend zur Mössbauerspektroskopie (MS) durchgeführt. Weitere Informationen über magnetische Struktur und Relaxationseigenschaften der Partikel ergaben sich aus Röntgenbeugungsexperimenten (XRD), Ferromagnetischer Resonanz (FMR) und SQUID-Magnetometrie. Um den Einfluss interpartikulärer Wechselwirkung auf Néelsche Relaxation als primären Relaxationsmechanismus kleiner Nanopartikel zu untersuchen, wurde das Relaxationsverhalten verschieden dick beschichteter 6 nm Eisenoxidpartikel verglichen. Neben einem geringen Effekt der Beschichtung auf die statische magnetische Struktur der Partikel konnte eine deutliche Änderung der Néelschen Relaxationsrate nachgewiesen werden. Im Vergleich beschichteter Magnetitpartikel von 6 - 26 nm in Glycerollösung konnte der Übergang von Néelschem Superparamagnetismus zum (Pseudo-)Superparamagnetismus hervorgerufen durch Brownsche Bewegung beobachtet werden, was es ermöglichte beide Prozesse bei verschiedenen Temperaturen und externen Magnetfeldern zu studieren. Auf diese Weise konnten zum ersten Mal Parameter beider Relaxationsmechanismen gleichzeitig mittels Mössbauerspektroskopie ermittelt werden. Im direkten Vergleich von Mössbauerspektroskopie- und AC-Suszeptometriemessungen wurde in eingehenden Untersuchungen von Hämatitnanospindeln in Ferrohydrogelen die Einschränkung der Partikelmobilität abhängig von der Vernetzungsdichte des Hydrogels untersucht, wobei in den letztgenannten ACS-Experimenten keine Anzeichen magnetischer Relaxation erkennbar waren. Dieser scheinbare Widerspruch konnte unter Berücksichtigung eingeschränkter Partikelbewegung in räumlich begrenzten Polymermaschen und den beiden Techniken zugänglichen Zeitskalen und Relaxationsarten erklärt werden. Ein ähnlicher Ansatz wurde genutzt, um die Brownsche Bewegung Ölsäure-beschichteter Magnetit-Partikelcluster in verschiedenen Polymerarten quantitativ zu bestimmen. Aufbauend auf der Analyse der magnetischen Struktur und Diffusionsbewegung wurden Beiträge Néelscher und Brownscher Relaxation in detaillierten AC-Suszeptometriemessungen identifiziert und interpretiert, was zudem die Abschätzung der hydrodynamischen Clustergröße ermöglichte

Whither Magnetic Hyperthermia? A Tentative Roadmap

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia

Whither Magnetic Hyperthermia? A Tentative Roadmap

The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia.This work was supported by the NoCanTher project, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 685795. The authors acknowledge support from the COST Association through the COST actions "RADIOMAG" (TD1402) and "MyWAVE" (CA17115). D.O., A.S.-O. and I.R.-R. acknowledge financial support from the Community of Madrid under Contracts No. PEJD-2017-PRE/IND-3663 and PEJ-2018-AI/IND-11069, from the Spanish Ministry of Science through the Ramon y Cajal grant RYC2018-025253-I and Research Networks RED2018-102626-T, as well as the Ministry of Economy and Competitiveness through the grants MAT2017-85617-R, MAT2017-88148R and the "Severo Ochoa" Program for Centers of Excellence in R&D (SEV-2016-0686). M.B. and N.T.K.T. would like to thank EPSRC for funding (grant EP/K038656/1 and EP/M015157/1) and AOARD (FA2386-171-4042) award. This work was additionally supported by the EMPIR program co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation program, grant no. 16NRM04 "MagNaStand". The work was further supported by the DFG grant CRC "Matrix in Vision" (SFB 1340/1 2018, no 372486779, project A02)

Magnetic Nanoparticle Systems for Nanomedicine—A Materials Science Perspective

Iron oxide nanoparticles are the basic components of the most promising magneto-responsive systems for nanomedicine, ranging from drug delivery and imaging to hyperthermia cancer treatment, as well as to rapid point-of-care diagnostic systems with magnetic nanoparticles. Advanced synthesis procedures of single- and multi-core iron-oxide nanoparticles with high magnetic moment and well-defined size and shape, being designed to simultaneously fulfill multiple biomedical functionalities, have been thoroughly evaluated. The review summarizes recent results in manufacturing novel magnetic nanoparticle systems, as well as the use of proper characterization methods that are relevant to the magneto-responsive nature, size range, surface chemistry, structuring behavior, and exploitation conditions of magnetic nanosystems. These refer to particle size, size distribution and aggregation characteristics, zeta potential/surface charge, surface coating, functionalization and catalytic activity, morphology (shape, surface area, surface topology, crystallinity), solubility and stability (e.g., solubility in biological fluids, stability on storage), as well as to DC and AC magnetic properties, particle agglomerates formation, and flow behavior under applied magnetic field (magnetorheology)

OPM magnetorelaxometry in the presence of a DC bias field

Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP’s magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNP’s relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to 100μT. We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNP’s alignment direction. Further, not only the relaxation process of the MNP’s magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field. © 2020, The Author(s)

The aggregation and reduction of iron minerals by the Alzheimer’s disease peptide ß-amyloid (1-42): an X-ray absorption study

Iron is vital for healthy brain function. However when present in a redox-active form or in excess concentrations it can be toxic. Interestingly, increased levels of redox-active iron biominerals have been shown to exist in Alzheimer’s disease (AD) tissues, including lesions comprised of the AD peptide β-amyloid (Aβ). These iron phases are capable of producing reactive oxygen species, resulting in the generation of oxidative stress manifesting as neuronal injury. As oxidative stress and the accumulation of iron are recognised as early stage events in AD, the presence of redox-active iron may prove fundamental in the development of AD pathology. The origin of these redox-active iron biominerals is unclear but recent studies suggest their formation may involve the interaction of Aβ with unbound brain iron and/or the malfunction of the iron storage protein ferritin. Despite these observations, the relationship between Aβ and iron is poorly understood, and the products of Aβ/iron interaction remain unknown. In this thesis, synchrotron-based x-ray techniques are combined with traditional biological approaches to examine the interactions between Aβ and various synthetic and naturally occurring iron forms. Through this methodology Aβ is shown to incorporate ferric iron phases into its fibrillar structure in vitro, with this interaction resulting in the chemical reduction of iron into a redox-active state. Further to this, Aβ is demonstrated to disrupt ferritin structure resulting in the chemical reduction of its redox-inactive iron core in vitro. Additionally the interaction of Aβ with crystalline iron phases is shown destroy iron crystal structure. Finally, redox-active iron is shown to be associated with regions of AD pathology, including fibrillar Aβ-like structures, within a transgenic mouse model of AD in situ. These findings suggest an origin for the redox-active iron forms and oxidative stress previously witnessed in AD tissue, thereby shedding light on the process of AD pathogenesis

Spin canting across core/shell Fe3O4/MnxFe3−xO4 nanoparticles

Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin configurations is important for optimizing these applications. The measured magnetization of MNPs can be significantly lower than bulk counterparts, often due to canted spins. This has previously been presumed to be a surface effect, where reduced exchange allows spins closest to the nanoparticle surface to deviate locally from collinear structures. We demonstrate that intraparticle effects can induce spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm diameter, core/shell Fe3O4/MnxFe3−xO4 MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy, x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular magnetic correlations, suggesting multiparticle coherent spin canting in an applied field. Atomistic simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI can lead to magnetic frustration within the shell and cause canting of the net particle moment. These results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the whole of the particle, rather than solely at the surface