THE CONDUCTANCE THROUGH a single-molecule molecular wire can be controlled by changing where an electrode contacts it, chemist Colin P. Nuckolls of Columbia University reported last week at the American Chemical Society national meeting in Anaheim, Calif., and in a recent Nano Letters paper (DOI: 10.1021/nl104411f ). The resulting device behaves as a single-molecule potentiometer, a variable resistor that can control electronic devices. Nuckolls, physicist Latha Venkataraman, and their coworkers connected both ends of oligoacetylene molecular wires to gold electrodes and measured the system’s conductance. They found that the conductance through the molecule depends on where the electrode binds to it. The electrodes can contact the molecules at their terminal sulfides or at any point along the conductive conjugated backbone, Nuckolls said. Nuckolls likens the double bonds in the oligoacetylene chain to the rungs of a ladder. Each time the electrode steps past a rung, “it changes the resistance because you’...