Mobile paramagnetic nanoparticle-based vortex for targeted cargo delivery in fluid

Microrobots are considered as potential candidates for targeted delivery of cargos, drugs and even energy with high precision. One interesting phenomenon is their collective behaviour actuated by dynamic fields, which is yet to be adequately studied. Herein, we report a novel method of using millions of magnetic nanoparticles to generate a dynamic-equilibrium particle-based vortex, which can manipulate multiple cargos simultaneously at the microscale. The governing physical laws of the generation of a particle-based vortex are explained and the experimental results are presented. The high effectiveness of this micro-vortex-based method of particle gathering is testified. Moreover, the vortex can be navigated near a solid surface in a controlled manner. The velocity and morphology of the mobile vortices with different pitch angles are investigated, showing that the vortex moving with small pitch angles is capable of maintaining the original shape and coverage area. Collecting and transporting multiple polystyrene (PS) microbeads into a channel using the vortex are also demonstrated. This method allows us to perform micromanipulation using the collective behaviour of nanoparticles and to develop new strategies for the formation and control of the microrobotic swarm.