Rietberg Max Tigo, Waanders Sebastiaan, Horstman-van de Loosdrecht Melissa Mathilde, Wildeboer Rogier R, Ten Haken Bennie, Alic Lejla
Magnetic Detection & Imaging Group, Technical Medical Centre, University of Twente, 7522 NH Enschede, The Netherlands.
Nanomaterials (Basel). 2021 Dec 15;11(12):3396. doi: 10.3390/nano11123396.
The efficient development and utilisation of magnetic nanoparticles (MNPs) for applications in enhanced biosensing relies on the use of magnetisation dynamics, which are primarily governed by the time-dependent motion of the magnetisation due to externally applied magnetic fields. An accurate description of the physics involved is complex and not yet fully understood, especially in the frequency range where Néel and Brownian relaxation processes compete. However, even though it is well known that non-zero, non-static local fields significantly influence these magnetisation dynamics, the modelling of magnetic dynamics for MNPs often uses zero-field dynamics or a static Langevin approach. In this paper, we developed an approximation to model and evaluate its performance for MNPs exposed to a magnetic field with varying amplitude and frequency. This model was initially developed to predict superparamagnetic nanoparticle behaviour in differential magnetometry applications but it can also be applied to similar techniques such as magnetic particle imaging and frequency mixing. Our model was based upon the Fokker-Planck equations for the two relaxation mechanisms. The equations were solved through numerical approximation and they were then combined, while taking into account the particle size distribution and the respective anisotropy distribution. Our model was evaluated for Synomag-D70, Synomag-D50 and SHP-15, which resulted in an overall good agreement between measurement and simulation.
磁性纳米颗粒（MNPs）在增强生物传感应用中的高效开发和利用依赖于磁化动力学的应用，而磁化动力学主要由外部施加磁场导致的随时间变化的磁化运动所支配。对其中涉及的物理过程进行准确描述很复杂且尚未完全理解，特别是在奈尔和布朗弛豫过程相互竞争的频率范围内。然而，尽管众所周知非零、非静态的局部场会显著影响这些磁化动力学，但MNPs的磁动力学建模通常采用零场动力学或静态朗之万方法。在本文中，我们开发了一种近似方法来对暴露于振幅和频率变化磁场中的MNPs进行建模并评估其性能。该模型最初是为预测差分磁强计应用中的超顺磁性纳米颗粒行为而开发的，但它也可应用于类似技术，如磁粒子成像和频率混合。我们的模型基于两种弛豫机制的福克 - 普朗克方程。通过数值近似求解这些方程，然后在考虑颗粒尺寸分布和各自的各向异性分布的情况下将它们组合起来。我们对Synomag - D70、Synomag - D50和SHP - 15进行了模型评估，结果测量值与模拟值总体吻合良好。
