Size and property bimodality in magnetic nanoparticle dispersions: single domain particles vs. strongly coupled nanoclusters

Abstract

The widespread use of magnetic nanoparticles in the biotechnical sector puts new demands on fast and quantitative characterization techniques for nanoparticle dispersions. In this work, we report the use of asymmetric flow field-flow fractionation (AF4) and ferromagnetic resonance (FMR) to study the properties of a commercial magnetic nanoparticle dispersion. We demonstrate the effectiveness of both techniques when subjected to a dispersion with a bimodal size/magnetic property distribution: i.e., a small superparamagnetic fraction, and a larger blocked fraction of strongly coupled colloidal nanoclusters. We show that the oriented attachment of primary nanocrystals into colloidal nanoclusters drastically alters their static, dynamic, and magnetic resonance properties. Finally, we show how the FMR spectra are influenced by dynamical effects; agglomeration of the superparamagnetic fraction leads to reversible line-broadening; rotational alignment of the suspended nanoclusters results in shape-dependent resonance shifts. The AF4 and FMR measurements described herein are fast and simple, and therefore suitable for quality control procedures in commercial production of magnetic nanoparticles.

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

“…These observations verify that the samples FS-XS→XXL contain in fact distinct fractions of core-clusters with systematically increasing size. Considering that for isometric clusters we would expect a bell-like shape of P (r), the elongated shape of the experimentally determined distributions for all seven samples suggests that the clusters tend to be anisotropic, as also observed by electron microscopy in [21].…”

Monocorevs.multicore magnetic iron oxide nanoparticles: uptake by glioblastoma cells and efficiency for magnetic hyperthermia

“…by a factor ∼10 only ( × < 5 • 10 9 A•m −1 •s −1 ), as proposed by Dutz and Hergt. 13 As reported in literature, [14][15][16] higher specific heating rates of multicore IONPs as compared to single core IONPs are ascribed to "spin glass" dynamics of the magnetic moments within a cluster, strongly correlated by the exchange interaction. This collective behaviour enhances the magnetic susceptibility, i.e.…”

Enhanced Methods to Estimate the Efficiency of Magnetic Nanoparticles in Imaging

“…FeraSpin R consists of elementary crystallites of iron-oxide, nominally γ-Fe 2 O 3 , with a diameter of 5–7 nm, according to which some of these crystallites aggregate to form particles with a larger diameter, such that there is a broader distribution due to these multi-cores [ 20 ] ( Figure 1 ). The mean hydrodynamic diameter is 60 nm.…”

“…A series of different multi-core size fractions have been isolated from FeraSpin R, namely, FeraSpin XS, FeraSpin M and FeraSpin XL, in which each fraction has a narrower multi-core size distribution than the parent material, and a mean hydrodynamic diameter of 15 nm, 35 nm, and 55 nm, respectively ( Figure 1 a). The magnetic core of FeraSpin XS has been shown from transmission electron microscopy (TEM) to be on the order of the elementary crystallites, with a mean of 5.8 nm, whereas FeraSpin L (not studied here) has larger aggregates with a mean magnetic core size of 33 nm [ 20 ]. Therefore, the average particle size of the fractions increases from XS to XL.…”

“…Therefore, the average particle size of the fractions increases from XS to XL. Although several studies have been made on FeraSpin R and the FeraSpin series in relation to their performance in MPI [ 17 , 18 , 20 , 21 , 22 , 23 ], this study performs a more detailed magnetic characterization on the immobilized particles. The magnetic properties of the immobilized particles are compared to the magnetic properties and image performance of Resovist.…”