Motion of nanometer sized magnetic particles in a magnetic field gradient

Abstract

Using magnetic particles with sizes in the nanometer range in biomedical magnetic separation has gained much interest recently due to their higher surface area to particle volume and lower sedimentation rates. In this paper, we report our both theoretical and experimental investigation of the motion of magnetic particles in a magnetic field gradient with particle sizes from 425 nm down to 50 nm. In the experimental measurements, we monitor the absorbance change of the sample volume as the particle concentration varies over time. We also implement a Brownian dynamics algorithm to investigate the influence of particle interactions during the separation and compare it to the experimental results for validation. The simulation agrees well with the measurements for particle sizes around 425 nm. Some discrepancies remain for smaller particle sizes, which may indicate that additional factors also influence the separation for the smaller size range. We observe that the separation process includes the formation of chainlike particle aggregates due to the magnetic dipole-dipole interactions between particles when subjected to an external magnetic field. We can also see that the hydrodynamic interaction between these chains contributes to reducing the separation time. In conclusion, we show that the formation of these particle aggregates, and to a less extent the hydrodynamic interactions between them contributes to significantly enhancing the particle separation process.

Uptake and Transport of Superparamagnetic Iron Oxide Nanoparticles through Human Brain Capillary Endothelial Cells

“…The magnetic core of the particles consists of approximately 101 single-domain magnetite crystallites of 12.3 nm each, and the intrinsic magnetization (M s ) of the particle is 350 kA/m. 39 Both red and blue fluorescent SPIONs were used in this study. The blue fluorescent nanoparticles have maximal excitation at 378 nm and emission at 413 nm, and red nanoparticles have an excitation wavelength of 578 nm and an emission wavelength of 613 nm.…”

Self-assembly processes of superparamagnetic colloids in a quasi-two-dimensional system

“…This can be studied numerically (Langevin dynamics simulations [14,19,20]) and theoretically (Smoluchowsky rate equations [16,17,21]). (4) The respective cases of the formation process and energy barriers should be taken into account [25].…”

“…It is noticed that the latter approach depends on a free parameter h (the effective interaction range averaged over the attractive region), and the long time saturated regime is not addressed. Later, the transient and long range equilibrium dynamics are obtained with Langevin dynamics simulations [14,19,20] and in experimental results [12,13,16,17,21]. The evolution of the mean length of the aggregatess(t) scales with t z [15] until the saturation regime, where it converges to a constant value [s(t) →s] in thermodynamic equilibrium after a transient time (t → t sat ).…”

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