Electrochemical reactivity at redox-molecule-based nanoelectrode ensembles

A model describing electrochemical reactivity at nanoelectrode ensembles co nsisting of redox-molecule-based active sites immobilized on otherwise pass ivated electrode surfaces is presented. A mathematical treatment in terms o f hemispherical diffusion of redox-active solutes to a layer of independent molecule-based nanoelectrode sites is shown to be equivalent to one in ter ms of a bimolecular diffusion-limited reaction between a layer of immobiliz ed redox molecules and a reservoir of redox-active solutes. This equivalenc e derives from the fact that in both cases the mass-transfer problem is ess entially that of hemispherical diffusion. The model is further developed to consider rate limitation by both the bimolecular redox reaction between th e active-site molecule and redox molecules in solution and the heterogeneou s redox reaction between the electrode and the active-site molecule. Analyt ical expressions are derived for the current-voltage relation corresponding to catalyzed electron transfer at an ensemble of redox-molecule-based nano electrode sites, and the expressions are used to interpret preliminary data for ultrasensitive electrochemical detection in how streams via an electro chemical amplification process that is thought to involve redox mediation b y individual analyte molecules adsorbed onto monolayer-coated electrodes. ( C) 2001 Elsevier Science B.V. All rights reserved.