Nanoscale Inorganic Motors Driven by Light: Principles, Realizations, and Opportunities

The prospect of self-propelled artificial machines small enough to navigate within biological matter has fascinated and inspired researchers and the public alike since the dawn of nanotechnology. Despite many obstacles toward the realization of such devices, impressive progress on the development of its basic building block, the nanomotor, has been made over the past decade. Here, we review this emerging area with a focus on inorganic nanomotors driven or activated by light. We outline the distinct challenges and opportunities that differentiate nanomotors from micromotors based on a discussion of how stochastic forces influence the active motion of small particles. We introduce the relevant light-matter interactions and discuss how these can be utilized to classify nanomotors into three broad classes: nanomotors driven by optical momentum transfer, photothermal heating, and photocatalysis, respectively. On the basis of this classification, we then summarize and discuss the diverse body of nanomotor literature. We finally give a brief outlook on future challenges and possibilities in this rapidly evolving research area.