Electrochemical Detection of Single Molecules

The electrochemical behavior of a single molecule can be observed by trapping a small volume of a dilute solution of the electroactive species between an ultramicroelectrode tip with a diameter of ∼15 nanometers and a conductive substrate. A scanning electrochemical microscope was used to adjust the tip-substrate distance (∼10 nanometers), and the oxidation of [(trimethylammonio)methyl] ferrocene (Cp 2 FeTMA + ) to Cp 2 FeTMA 2+ was carried out. The response was stochastic, and anodic current peaks were observed as the molecule moved into and out of the electrode-substrate gap. Similar experiments were performed with a solution containing two redox species, ferrocene carboxylate (Cp 2 FeCOO - ) and Os(bpy) 3 2+ (bpy is 2,2′-bipyridyl).