Chen La, Offenhäusser Andreas, Krause Hans-Joachim
Institute of Bioelectronics (ICS-8/PGI-8), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
Rev Sci Instrum. 2015 Apr;86(4):044701. doi: 10.1063/1.4916255.
As a powerful and versatile scientific instrument, magnetic tweezers have been widely used in biophysical research areas, such as mechanical cell properties and single molecule manipulation. If one wants to steer bead position, the nonlinearity of magnetic properties and the strong position dependence of the magnetic field in most magnetic tweezers lead to quite a challenge in their control. In this article, we report multi-pole electromagnetic tweezers with high permeability cores yielding high force output, good maneuverability, and flexible design. For modeling, we adopted a piece-wise linear dependence of magnetization on field to characterize the magnetic beads. We implemented a bi-linear interpolation of magnetic field in the work space, based on a lookup table obtained from finite element simulation. The electronics and software were custom-made to achieve high performance. In addition, the effects of dimension and defect on structure of magnetic tips also were inspected. In a workspace with size of 0.1 × 0.1 mm(2), a force of up to 400 pN can be applied on a 2.8 μm superparamagnetic bead in any direction within the plane. Because the magnetic particle is always pulled towards a tip, the pulling forces from the pole tips have to be well balanced in order to achieve control of the particle's position. Active video tracking based feedback control is implemented, which is able to work at a speed of up to 1 kHz, yielding good maneuverability of the magnetic beads.
作为一种强大且多功能的科学仪器，磁镊已广泛应用于生物物理研究领域，如细胞力学特性和单分子操纵。如果想要控制珠子的位置，大多数磁镊中磁特性的非线性以及磁场对位置的强烈依赖性会给控制带来相当大的挑战。在本文中，我们报道了一种具有高磁导率磁芯的多极电磁镊，其具有高力输出、良好的可操纵性和灵活的设计。为了进行建模，我们采用了磁化强度与磁场的分段线性依赖关系来表征磁珠。我们基于从有限元模拟获得的查找表，在工作空间中实现了磁场的双线性插值。电子设备和软件都是定制的，以实现高性能。此外，还研究了尺寸和缺陷对磁尖端结构的影响。在尺寸为0.1×0.1 mm²的工作空间中，可以在平面内的任何方向上对一个2.8μm的超顺磁珠施加高达400 pN的力。由于磁性粒子总是被拉向一个尖端，为了实现对粒子位置的控制，来自磁极尖端的拉力必须很好地平衡。实现了基于主动视频跟踪的反馈控制，其能够以高达1 kHz的速度工作，使磁珠具有良好的可操纵性。
