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 between the tip and a substrate. Repeated electron transfers of an electroactive molecule as it shuttles by diffusion between tip and substrate produce a current (similar to 0.6 pA/molecule) that can be used to detect the trapped molecules. The tip electrode size and shape can be found from the electrode approach curves (current vs tip-to-substrate distance) based on approximate equations and digital simulations. Analysis of the observed fluctuating currents by autocorrelation, spectral density, and probability density functions is also described.