Interaction of a chemically propelled nanomotor with a chemical wave.

Self-propulsion on small scales is an ubiquitous phenomenon in biology. Bacteria and other microorganisms swim in order to obtain food or to respond to stimuli, molecular motors like ATP synthase are the engines that power swimming motion, and kinesin and other molecular motors are essential for active transport in the cell, participate in the DNA replication process and perform a variety of other essential tasks. More recently, there has been considerable interest in synthetic nanoand micrometer-scale self-propelled objects. 6] Chemists have fabricated a variety of nanomachines that either swim by unsymmetrical motions driven by external fields or utilize chemical reactions to effect directed motion. Theoretical models have been constructed to describe chemically powered nanomotors. Several supramolecular entities, such as pseudorotaxanes, rotaxanes, and catenanes, that can be used as molecular switches, molecular brakes, and rachets have been developed. Synthetic nanomotors with no moving parts and use chemical energy for their directed motion provide some of the simplest examples of self-propulsion on nanoand micrometer scales. These include bimetallic nanorods, Pt–silica sphere dimers, and Janus particles. There has also been a significant effort aimed at controlling the motion and transport of nanoscale objects by magnetic fields, microchannel networks, chemical sensing, and other means. The interest in these synthetic nanomachines stems from their potential applications: targeted drug delivery, pick up and delivery of cargo, motion-based biosensing, nanoscale assembly, targeted synthesis, nanoand microfluidics, collective oscillations, nanoactuators, etc. 23–30] It is well known that chemical systems which are displaced far from equilibrium may exhibit temporal oscillations and chaos or may self-organize to form spatially inhomogeneous patterns such as chemical waves in solution or on catalytic surfaces, Turing patterns, etc. Questions that naturally arise are, how do nanomotors move and respond to chemically active environments, and can the inhomogeneity in the environment be used to influence the dynamics of motors and possibly provide a way to control their motions? Here, we consider how a sphere dimer motor moves in a chemically active medium and interacts with a chemical wave. We find that a chemical wave is able to reflect a dimer motor (Figure 1) and suggest that this effect can provide a possible