Evolution of molecular machines: from solution to soft matter interface

In the molecular machine concept, single molecules and/or small molecular assemblies operate as independent machines in the ultimate miniaturization of functional systems. For the development of molecular machines, changing the medium of operation from solution to solid surface satisfies several demands for machine functions including allowing direct observation, enabling connection with devices and facilitation of sequential actions. However, the field of molecular machines on solid surfaces is still immature when compared with the sophisticated molecular mechanical systems observed in Nature. Required further developments of molecular machines include improved dynamic operations so that investigations of molecular machine functionality at dynamic interfacial media have become important. In this paper, the development of research on molecular machines in solution and at solid interfaces is described together with an introduction of recent challenges in the operation of molecular machines at soft matter interfaces.