Researchers from Cornell University unveiled a robot as small as a a single cell. Here’s more form Engadget:
The robots themselves are only 5 microns thick, 40 microns wide and between 40 and 70 microns long, depending on the design. The brain and body consist of a silicon photovoltaic circuit while the legs are made from a quartet of electrochemical actuators.
“In the context of the robot’s brains, there’s a sense in which we’re just taking existing semiconductor technology and making it small and releasable,” [Cornell professor Paul McEuen] told Cornell News. “But the legs did not exist before. There were no small, electrically activatable actuators that you could use. So we had to invent those and then combine them with the electronics.”