Time and spatial dependence of the concentration of less than 105 microelectrode-generated molecules

The time and spatial dependence of the concentration of as few as 40,000 electrogenerated, redox-active molecules has been determined. The distance between generator and detector microelectrodes in an array used in the study could be varied from 0.8 to 28 micrometers. Measurements of a sufficiently small ensemble of molecules allowed the experimental results to be compared with a quantitative simulation of the random movement of each member of the ensemble. The transit time of an electrogenerated species from the generator to a collector microelectrode was measured as a function of viscosity, diffusivity, and distance.