Chemical locomotion.

Research into the autonomous motion of artificial nano- and microscale objects provides basic principles to explore possible applications, such as self-assembly of superstructures, roving sensors, and drug delivery. Although the systems described have unique propulsion mechanisms, motility in each case is made possible by the conversion of locally available chemical energy into mechanical energy. The use of catalysts onboard can afford nondissipative systems that are capable of directed motion. Key to the design of nano- and micromotors is the asymmetric placement of the catalyst: its placement in an environment containing a suitable substrate translates into non-uniform consumption of the substrate and distribution of reaction products, which results in the motility of the object. These same principles are exploited in nature to effect autonomous motion.