Magnetic Colloidal Currents Guided on Self‐Assembled Colloidal Tracks

The nondiffusive directional transport of micro‐cargos, such as colloids, cells, or liposomes, is vital for living organisms, for example in the intracellular transport of cytoplasmic organelles along actin filaments or microtubules, and also in numerous applications in biomedicine and nanotechnology. Mimicking natural designs, the self‐assembly capacity of magnetic colloids is studied and exploited to construct different paths along which swarms of magnetic micro/nanoparticles can be guided. Driven transport is possible thanks to the combined effect of the magnetic microstructure of the self‐assembled tracks, adsorbed on a solid interface, and the application of a time‐dependent magnetic field. Nonadsorbed magnetic particles propel along the pre‐formed structures under the action of an externally controllable traveling potential ratchet, like molecular walkers. The transport mechanisms are determined by both the properties of the particles and the configuration of the applied field. Finally, it is shown how the proposed combination of self‐assembly and guided transport paves the way to the development of a new class of techniques, able to adapt ad hoc to the environment, and transport of microparticles along irregular profiles and/or crowded conditions. The technological interest is immediate, including drug delivery and controlled guidance of microcargos, in biological environments and microfluidic platforms.