Diffusional interaction between closely spaced dual microelectrodes

Electrode assemblies with a pair of independent carbon fiber microelectrodes (diameter = 10 mu m) were constructed with gap distances from <1 mu m to 30 mu m. The tips of these electrodes have overall diameters of between 20 and 60 mu m. Scanning electrochemical microscopy (SECM) was used in the feedback mode to measure the distance between the electrodes. Diffusional interaction between the two electrodes was investigated and then modeled by convolution of the concentration produced by the generator electrode with the impulse response function for a spherically divergent source. This impulse response function was calculated using the electrode spacing measured with SECM, the generator electrode radius experimentally determined from steady-state voltammetry, and the diffusion coefficient of the analyte. This convolution method successfully predicted the collector electrode response to any applied waveform when the concentration produced by the generator electrode was calculated from the Nernst equation. If desired, diffusional interaction between the electrodes can be nearly eliminated while retaining the same tip dimensions by employing a two-step beveling procedure. (C) 1999 Elsevier Science B.V. All rights reserved.