Abstract
In the present study, we applied a regularized inversion method to extract the particle size, magnetic moment and relaxation-time distribution of magnetic nanoparticles from small-angle x-ray scattering (SAXS), DC magnetization (DCM) and AC susceptibility (ACS) measurements. For the measurements the particles were colloidally dispersed in water. At first approximation the particles could be assumed to be spherically shaped and homogeneously magnetized single-domain particles. As model functions for the inversion, we used the particle form factor of a sphere (SAXS), the Langevin function (DCM) and the Debye model (ACS). The extracted distributions exhibited features/peaks that could be distinctly attributed to the individually dispersed and non-interacting nanoparticles. Further analysis of these peaks enabled, in combination with a prior characterization of the particle ensemble by electron microscopy and dynamic light scattering, a detailed structural and magnetic characterization of the particles. Additionally, all three extracted distributions featured peaks, which indicated deviations of the scattering (SAXS), magnetization (DCM) or relaxation (ACS) behavior from the one expected for individually dispersed, homogeneously magnetized nanoparticles. These deviations could be mainly attributed to partial agglomeration (SAXS, DCM, ACS), uncorrelated surface spins (DCM) and/or intra-well relaxation processes (ACS). The main advantage of the numerical inversion method is that no ad hoc assumptions regarding the line shape of the extracted distribution functions are required, which enabled the detection of these contributions. We highlighted this by comparing the results with the results obtained by standard model fits, where the functional form of the distributions was a priori assumed to be log-normal shaped.
Highlights
As evident from recent review articles [1,2,3,4], biomedical application of magnetic iron oxide nanoparticles (IONPs) is presently an intensely investigated, multi-disciplinary field of research
The pH value of the final water-based colloidal dispersion of the nanoparticles was adjusted to 7. This colloidal dispersion was directly measured by small-angle x-ray scattering (SAXS), DC magnetization (DCM) and AC susceptibility (ACS) without any sample modification, for ACS the sample was diluted ten-fold with distilled water
The isothermal DCM measurement of the colloidal dispersion of IONPs was performed at 300 K in a magnetic property measurement system (MPMS XL, Quantum Design, USA)
Summary
H Gavilán, D González-Alonso, I de Pedro, L Fernández Barquín and C Johansson. H Gavilán, D González-Alonso, I de Pedro, L Fernández Barquín and C Johansson11 Original content from this Krakow, Poland work may be used under the terms of the Creative. Commons Attribution 3.0 8 Lund Centre for Field-Flow Fractionation, Department of Food Technology, Engineering and Nutrition, Lund University, SE-223 63 licence. Any further distribution of 9 Instituto de Ciencia de Materiales de Madrid, ICMM/CSIC, E-28049 Madrid, Spain this work must maintain 10 Departmento CITIMAC, Faculty of Science, University of Cantabria, E-39005 Santander, Spain attribution to the
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