SINGLE-MOLECULE ELECTROCHEMISTRY

By using specially constructed nanometer tips of sharpened Pt-Ir wire in a wax sheath, small numbers of molecules (1-10) can be trapped betw een the tip and a substrate. Repeated electron transfers of an electro active molecule as it shuttles by diffusion between tip and substrate produce a current (similar to 0.6 pA/molecule) that can be used to det ect the trapped molecules. The tip electrode size and shape can be fou nd from the electrode approach curves (current vs tip-to-substrate dis tance) based on approximate equations and digital simulations. Analysi s of the observed fluctuating currents by autocorrelation, spectral de nsity, and probability density functions is also described.