http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2005/06/02/MNGUOD1V1P1.DTL
"Wolkow said his team demonstrated that a molecule could be controllably charged by a single atom while all adjacent atoms remained neutral."

"Basically, Wolkow's transistor works like this:
The natural electrostatic field from a single silicon atom is permitted to flow through a hydrocarbon molecule bonded to a silicon crystal substrate. One end of the molecule is the "in" electrode, and the other is the "out" electrode; the electricity is then conducted through the hydrocarbon molecule to the tip of a hovering electron tunneling microscope. The microscope tip is the "controlling" electrode -- the on/off switch."

Coming soon: single-quark transistor.