Nanotransport controlled by means of the ratchet effect

The directional motion of micro- and nanoparticles can be induced not only directly due to the effect of forces with a nonzero average value, which set the direction of the motion, but also, in the absence of such forces in systems with broken mirror symmetry, under the effect of nonequilibrium fluctuations of various natures (the motor or ratchet effect). Unlike other reviews on nanoparticle transport, we focus on the principles of nanotransport control by means of the ratchet effect, which has numerous practical applications and, in particular, is a promising mechanism for targeted delivery of drugs in living organisms. We explain in detail various techniques to arrange directional motion in asymmetric media by means of rectification of the nonequilibrium fluctuations that supply energy to the system and feature a zero average value of applied forces, whether actual or generalized. We consider in depth the properties and characteristics of ratchet systems, their dependences on temperature, load forces, and features of the periodic potential profile in which nanoparticles move, such as the frequency of fluctuations of this profile and its spatial and time asymmetry. A systematic description of factors that determine the direction of motion of ratchet systems is presented.