Catalytically propelled micro-/nanomotors: how fast can they move?

Synthetic micro-/nanomotors represent one of the most exciting challenges facing nanotechnology and hold considerable promise for diverse future applications. This review discusses different strategies to improve the speed of the catalytic nanomotors, summarizing and comparing the maximum absolute and relative speeds obtained with different catalytically propelled micro-/nanomotors. Remarkably ultrafast nanowires and microtube engines, with speeds of 60 and 375 body lengths s(-1), respectively, have been developed recently. Achieving such amazingly high speed and power has been accomplished through rational optimization of key factors governing the propulsion behavior, including composition of the motor and fuel, the motor morphology and various external stimuli. We hope that our discussion will serve as a guide to the rational design of even faster and more powerful catalytically propelled fuel-efficient micro-/nanomotors, with speed limits that are limited only by our imagination.