Detection of heavy metal ions based on quantum point contacts

We report on a method to detect trace amounts of metal ions using electrodes separated by atomic scale gaps. By sweeping the electrode potentials cathodically, we deposit metal ions into the gap and form a point contact between the two electrodes, which triggers a quantum jump in the conductance. The deposition time required to form the point contact increases as the ion concentration decreases. We can also dissolve the point contact by sweeping the potentials anodically, which causes a sharp decrease in the conductance. The potentials at which a point contact is formed and dissolved provides the identity of the ions.