The one-molecule size 4x4

Nature magazine reports how Groningen chemist Ben Feringa and a group of researchers from Swiss group Empa managed to built the smallest electric vehicle yet. This improves on the group's 2004 award-winning invention of a light-powered molecular motor.
Their new 4x4, shaped in a single molecule, features the equivalent of "motors" on each wheel and gets its power from an overhead supply - in this case the tip of a scanning tunneling microscope.
The reseachers say a 500-millivolt charge rotates the wheels about 180 degrees.
Chemists is not quite sure how it works, but surmise that "electrons tunnel through the molecule, causing reversible structural changes in each motor/wheel."

Ben Faringa

Its builders do not call it a tiny car but a"molecular transport machine," and hope to power future versions with laser to deliver medicine precisely where needed or repair/destroy cell structures in the human body.
Like the seven years it took to get here, the next step may take a while yet. The nano works only at cryogenic temperatures, on copper inside a vacuum.