Motility of Coupled Swimmers

我们将利用先进的DNA技术来构建耦合的热渗透游泳体，并研究它们的运动性。我们的方法的一个独特之处是内置的力传感器，它将允许在原位测量耦合游泳者推进所涉及的力，从而推导出自推进运动的物理描述。力传感器是通过双链DNA分子将主动驱动的Janus粒子与被动负载粒子耦合实现的。由于DNA的力-距离关系是众所周知的，当整个整体被推进时，这种设置允许通过测量粒子之间的距离直接推导局部力。激光诱导推进将利用Janus粒子作为主动游泳者来实现。Janus粒子是聚苯乙烯微球，在一个半球上有一层薄薄的金层，在它的周围有一个不对称的温度，因此，当它们被激光照射时，会产生流场。DNA技术很容易地允许改变主动游泳者和货物颗粒之间的连接物的长度。通过这种方式，将构建耦合游泳者的排列，其中货物位于激光诱导流场的内部或外部，从而可以研究货物对局部流场的影响。通过改变激光照射的输入功率和货物颗粒的斯托克斯阻力产生的反作用力，我们计划推导出系统的重要物理参数，例如，Janus颗粒的失速力或旋转扩散时间。在初步的实验中，我们已经得到了拖曳货物可以减少旋转扩散的证据。在这里，我们计划详细研究这种行为，因为抑制旋转扩散是游泳者定向运动的一个重要要求。在此背景下，我们还计划通过DNA折纸技术构建和应用具有更高机械刚度的连接体。在计划项目的后期状态中，我们将重点研究复杂游泳者的运动性，其中不同数量的耦合活性Janus粒子可以同时驱动。这里的目标是确定速度和产生的力如何取决于驱动粒子的数量。这项任务将允许将人工游泳者的行为与生物系统进行比较，例如与已经得到充分研究的微管相关分子马达的运动进行比较。我们计划与来自莱比锡大学的长期合作伙伴进行可持续的合作——与Frank Cichos小组就他们的暗场设置进行测量，与Klaus Kroy小组就游泳者运动的理论描述进行合作。研究结果有望促进新的人工游泳者的创造。

We will harness advanced methods of DNA technology to construct coupled thermo-phoretic swimmers and to investigate their motility.A unique feature of our approach is a built-in force sensor which will allow to measure forces involved in the propulsion of coupled swimmers in situ, and thus, to derive a physical description of the self-propelled motion. The force sensor is realized by coupling of actively driven Janus particles and passive cargo particles by means of a double-stranded DNA molecule. Since the force-distance relation of DNA is well known, this setup allows deriving local forces directly by measuring the distance between the particles, when the whole ensemble is propelled.Laser-induced propulsion will be realized using Janus particles as active swimmers. The Janus particles are polystyrene microspheres with a thin gold layer on one hemisphere, around which an asymmetric temperature, and thus, flow field is generated when they are irradiated by laser light.DNA technology easily allows varying the length of the linker between the active swimmer and the cargo particle. In this way, arrangements of coupled swimmers will be constructed, where the cargo is positioned within or outside of the laser-induced flow field which allows to study the impact of the cargo on the local flow field. By varying both the input power of laser irradiation and the counteracting force created by the Stokes drag of the cargo particle, we plan to derive important physical parameters of the system, such as, e.g. stall force or rotational diffusion time of the Janus particle.In preliminary experiments we already got evidence that the rotational diffusion can be reduced by dragging cargo. Here we plan to investigate this behavior in detail, because the suppression of rotational diffusion is one important requirement for a directed movement of swimmers. In this context, we also plan to construct and to apply linkers with much higher mechanical stiffness by means of DNA origami technique.In the later state of the planned project, we will focus on the investigation of the motility of complex swimmers, where a varying number of coupled active Janus particles can be driven simultaneously. Here the goal is to determine, how both velocity and generated force depend on the number of driven particles. This task will allow comparing the behavior of artificial swimmers to biological systems, for example to the well-studied motility of microtubule-associated molecular motors.We plan a sustainable collaboration with our long-term partners from University Leipzig - with the group of Frank Cichos in terms of the measurements on their dark-field setup and with the group of Klaus Kroy concerning the theoretical description of the swimmer motility. The results are expected to facilitate the creation of new artificial swimmers.