Relating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers

Bender, Philipp; Fock, Jeppe; Frandsen, Cathrine; Hansen, Mikkel Fougt; Balceris, Christoph; Ludwig, Frank; Posth, Oliver; Wetterskog, Erik; Bogart, Lara K.; Southern, Paul; Szczerba, Wojciech; Zeng, Lunjie; Witte, Kerstin; Gruettner, Cordula; Westphal, Fritz; Honecker, Dirk; González-Alonso, David; Barquı́n, L. Fernández; Johansson, Christer

doi:10.1021/acs.jpcc.7b11255

Cited by 121 publications

(117 citation statements)

References 56 publications

(104 reference statements)

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“…Comparing the present samples to the nanoflowers studied in [35], subtle differences are observed. The nanoflowers were found to consist of intergrown seeds with a clear overlap but slightly varying orientations.…”

Section: Acs and Magnetic Hyperthermia Experimentsmentioning

confidence: 71%

“…The complex volume susceptibility χ(ω) = χ (ω) + iχ (ω) was measured with a custom-built setup described in [34], which uses an field amplitude of 95 µT, following the protocol described in [20]. By a numerical inversion of the ACS spectra we derived P (ω c ) [31,35]. The uncertainty was not known and we assumed for each data point a reasonable value of σ = 0.05 • χ max .…”

Section: Methodsmentioning

confidence: 99%

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Influence of clustering on the magnetic properties and hyperthermia performance of iron oxide nanoparticles

et al. 2018

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Clustering of magnetic nanoparticles can drastically change their collective magnetic properties, which in turn may influence their performance in technological or biomedical applications. Here, we investigate a commercial colloidal dispersion (FeraSpinR), which contains dense clusters of iron oxide cores (mean size around 9 nm according to neutron diffraction) with varying cluster size (about 18-56 nm according to small angle x-ray diffraction), and its individual size fractions (FeraSpinXS, S, M, L, XL, XXL). The magnetic properties of the colloids were characterized by isothermal magnetization, as well as frequency-dependent optomagnetic and AC susceptibility measurements. From these measurements we derive the underlying moment and relaxation frequency distributions, respectively. Analysis of the distributions shows that the clustering of the initially superparamagnetic cores leads to remanent magnetic moments within the large clusters. At frequencies below 10 rad s, the relaxation of the clusters is dominated by Brownian (rotation) relaxation. At higher frequencies, where Brownian relaxation is inhibited due to viscous friction, the clusters still show an appreciable magnetic relaxation due to internal moment relaxation within the clusters. As a result of the internal moment relaxation, the colloids with the large clusters (FS-L, XL, XXL) excel in magnetic hyperthermia experiments.

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Section: Acs and Magnetic Hyperthermia Experimentsmentioning

confidence: 71%

Section: Methodsmentioning

confidence: 99%

Influence of clustering on the magnetic properties and hyperthermia performance of iron oxide nanoparticles

et al. 2018

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“…From the SAXS data we derived the underlying correlation function C(r)r 2 by an indirect Fourier transform (IFT) [41,[66][67][68][69] of the radially averaged scattering intensity I(q) ( Fig. 1(b)).…”

Section: A Structural and Magnetic Pre-characterizationmentioning

confidence: 99%

Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

et al. 2018

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Here, we resolve the nature of the moment coupling between 10-nm DMSA-coated magnetic nanoparticles. The individual iron oxide cores were composed of > 95 % maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent AC susceptibility data in the superparamagnetic regime indicates a tendency for dipolar coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross-section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross-section. The correlation function suggests non-stochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core-clusters.

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“…The synomag-D nanoflowers were supplied by micromod Partikeltechnologie GmbH, Germany, which consist predominately of γ − Fe 2 O 3 , and are coated with dextran. A detailed study of these particles can be found in Bender et al 27 which showed that they are around 39 nm in size and consist of crystallites with sizes ranging from 5 − 15 nm. Transmission electron microscopy (TEM) images were taken with a FEI Titan 80-300 TEM, for which the sample was prepared by putting a small droplet of the dilute dispersion of the particles on a carbon-coated copper grid.…”

Section: Nanoflowersmentioning

confidence: 99%

Supraferromagnetic correlations in clusters of magnetic nanoflowers

Bender

Honecker

Barquı́n

2019

Applied Physics Letters

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Magnetic nanoflowers are densely packed aggregates of superferromagnetically coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia experiments. Here, we investigate the nature of the moment coupling within a powder of such nanoflowers using spin-resolved small-angle neutron scattering. Within the powder the nanoparticles are agglomerated to clusters, and we can show that the moments of neighboring nanoflowers tend to align parallel to each other. Thus, the whole system resembles a hierarchical magnetic nanostructure consisting of three distinct levels, i.e. (i) the ferrimagnetic nanocrystallites as building blocks, (ii) the superferromagnetic nanoflowers, and (iii) the supraferromagnetic clusters of nanoflowers. We surmise that such a supraferromagnetic coupling explains the enhanced magnetic hyperthermia performance in case of interacting nanoflowers.The working principle of magnetic hyperthermia (MHT) is to administer a moderate quantity of magnetic nanoparticles within tumors and to heat them up by applying alternating magnetic fields with clinically acceptable parameters (i.e. comparatively high frequencies 100 kHz but low amplitudes 20 mT 1,2 ) to kill the tumors. Additionally, a magnetomechanical actuation of the embedded particles may disrupt the cytoskeleton and lead to cell death. 3,4 In physiological environment nanoparticles usually agglomerate, which can significantly modify their magnetic properties compared to the dilute non-interacting case 5,6 and which in turn may alter their heating behavior. 7-10 Depending on the characteristics of the individual particles and the field parameters, such a clustering can either improve or impair the MHT performance. [11][12][13][14][15] In fact it was observed for so-called nanoflowers, which are densely packed aggregates of iron oxide crystallites, that they excel during MHT experiments compared to the singlecrystals 16 and other systems such as magnetosomes. 17 This intriguing result motivated numerous studies regarding synthesis and characterization of such flower-shaped particles. [18][19][20][21][22][23] It can be shown that an exchange coupling between the cores leads to a superferromagnetic magnetization state 24 within the individual nanoflowers, 25 but with a significant internal spin disorder caused by the high defect density, e.g. due to the grain boundaries. 26 It is speculated that such a disordered state enables an increased excitation of the moments 27,28 , similar to other defect-rich particles. 29 When introduced into tumors, it is safe to assume that the nanoflowers will agglomerate to clusters, and thus interparticle interactions will be relevant. 30 In Bender et al. 31 we could show for homogeneous superparamagnetic nanoparticles a predominance for antiferromagnetic-like moment correlations within particle clusters via polarized small-angle neutron scattering (SANS). In this work we use the same approach to determine the nature of the moment coupling within a powder of iron oxide a) Electronic mail: philipp.bender@uni...

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Relating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers

Cited by 121 publications

References 56 publications

Influence of clustering on the magnetic properties and hyperthermia performance of iron oxide nanoparticles

Influence of clustering on the magnetic properties and hyperthermia performance of iron oxide nanoparticles

Dipolar-coupled moment correlations in clusters of magnetic nanoparticles

Supraferromagnetic correlations in clusters of magnetic nanoflowers

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