Remotely powered self-propelling particles and micropumps based on miniature diodes

Microsensors and micromachines that are capable of self-propulsion through fluids could revolutionize many aspects of technology. Few principles to propel such devices and supply them with energy are known. Here, we show that various types of miniature semiconductor diodes floating in water act as self-propelling particles when powered by an external alternating electric field. The millimetre-sized diodes rectify the voltage induced between their electrodes. The resulting particle-localized electro-osmotic flow propels them in the direction of either the cathode or the anode, depending on their surface charge. These rudimentary self-propelling devices can emit light or respond to light and could be controlled by internal logic. Diodes embedded in the walls of microfluidic channels provide locally distributed pumping or mixing functions powered by a global external field. The combined application of a.c. and d.c. fields in such devices allows decoupling of the velocity of the particles and the liquid and could be used for on-chip separations. It is not easy to make small particles and devices that propel themselves in liquid. Viscous effects predominate on the microscale and render most mechanical means of propulsion inefficient1–4. The flagellar and ciliar bacterial motors are among the few natural chemical–mechanical ways of self-propulsion on the microscale5–8. Significant progress has been achieved in th