Motility of Coupled Swimmers

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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.