Stochastic sensing of single molecules in a nanofluidic electrochemical device.

We report the electrochemical detection of individual redox-active molecules as they freely diffuse in solution. Our approach is based on microfabricated nanofluidic devices, wherein repeated reduction and oxidation at two closely spaced electrodes yields a giant sensitivity gain. Single molecules entering and leaving the cavity are revealed as anticorrelated steps in the faradaic current measured simultaneously through the two electrodes.

Electrochemical correlation spectroscopy in nanofluidic cavities.

We introduce both theoretically and experimentally a new electrochemical technique based on measuring the fluctuations of the faradaic current during redox cycling. By analogy with fluorescence correlation spectroscopy (FCS), we refer to this technique as electrochemical correlation spectroscopy (ECS). We first derive an analytical expression of the power spectral density for the fluctuations in a thin-layer-cell geometry.

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.