Fast electron-transfer kinetics probed in nanofluidic channels.

We demonstrate that a 50 nm high solution-filled cavity bounded by two parallel electrodes in which electrochemically active molecules undergo rapid redox cycling can be used to determine very fast electron-transfer kinetics. We illustrate this capability by showing that the heterogeneous rate constant of Fc(MeOH)(2) sensitively depends on the type and concentration of the supporting electrolyte. These solid-state devices are mechanically robust and stable over time and therefore have the potential to become a widespread and versatile tool for electrochemical measurements.