Liquid mediated surface-particle interactions in near-surface motion of superparamagnetic particles and magnetic Janus microparticles in quiescent liquids

精确控制小磁颗粒（MP）的驱动为分析物检测和诊断（例如疾病标记物或病毒检测）新策略的开发开辟了新的途径。MP很有前途，因为目前还没有迹象表明用于驱动它们的磁场会改变生物物质。自21世纪初以来，外部随时间变化的磁场已经被叠加到静态磁场景观（MFLs）中，这些静态磁场景观来自磁荷阵列（在畴中、微磁体中或来自微导线中的电流）。通过这种方法，可以实现mp传输、流体混合、mp分离、mp分选，甚至可以通过巨磁电阻和霍尔效应传感器实现生物功能化MPs的传感。超强磁场的一个主要特征是在其产生的表面附近的小距离上有很强的场梯度。在这方面的大多数已知工作中，除了磁性相互作用外，mps与表面通过液体的相互作用被忽略了，并且在大多数研究中都使用了超顺磁性粒子。通过这一建议，我们希望从两个方面扩展对这些重要微系统的认识：我们希望(1)系统地研究液体介导的微系统与近表面之间的相互作用对微系统运动的影响，并探索(2)在微系统中具有磁帽的球形非磁性微粒子（磁性Janus粒子，MJPs）的不同运动类型（旋转和平移）。与它们的超顺磁粒子相比，这些特殊的粒子具有更大的磁矩，不仅可以平移，还可以定向和旋转。特别是，我们将建立一种技术，不仅可以自动跟踪2D-MP位置和mjp方向作为时间的函数（录制视频中的所有粒子），还可以自动跟踪它们在基片表面上的高度（3D跟踪）。这个实验确定的量将用于量化表面- MP相互作用对MP运动的影响。获得的理解将用于概念验证应用，其中病毒替代品（表面功能化的纳米颗粒）将通过表面上MP高度的变化来检测。

Precisely controlled actuation of small magnetic particles (MP) opens new avenues for the development of new strategies for analyte detection and diagnostics, e.g., for disease marker or virus detection. MP are promising as there is as yet no indication that the magnetic fields used for their actuation would modify biological matter. Since the early 2000s external time-dependent magnetic fields have been superposed for this purpose with static magnetic field landscapes (MFLs) emerging from arrays of magnetic charges (in domains, micromagnets, or from currents in micro wires). With this approach MP-transport, fluid mixing, MP-separation, MP-sorting, and even sensing of biologically functionalized MPs, e.g., via giant magnetoresistance and Hall-effect sensors has been achieved. A central characteristic of the MFLs are strong field gradients over small distances close to the surface from which the MFL emerges. In most of the known work in this context the interactions between MP and surface via the liquid, except for the magnetic interactions, have been neglected and in most of the studies superparamagnetic particles have been used. With this proposal we want to extend knowledge on these important micro systems by two aspects: We want to (1) systematically investigate the influence of the liquid mediated interactions between the MP and a close surface on the MP motion and explore (2) the different motion types (rotation and translation) of spherical non-magnetic micro particles with a magnetic cap (magnetic Janus particles, MJPs) in MFLs. These particular particles possess a much larger magnetic moment as compared to their superparamagnetic counterparts and may not only be translated but also oriented and rotated. In particular, we will establish a technique to automatically track not only the 2D-MP positions and MJP-orientations as functions of time (of all particles in a recorded video) but also their height over the substrate surface (3D tracking). This experimentally determined quantity will be used to quantify the influence of surface – MP interactions on the MP motion. The attained understanding will then be used for a proof-of-concept application, where a virus replacement (a surface-functionalized nano particle) shall be detected by a change in MP height over the surface.