How to understand and interpret current flow in nanopore/electrode devices.

Nanopore-based single-molecule sensors have become an important class of analytical devices that have in some cases already reached the market place. Traditionally operated in a two-electrode configuration, devices with three or more electrodes have emerged recently, for example with a view on switching the transport properties of the nanopore or even tunneling-based detection of analytes with the ultimate goal of inexpensive and ultrafast DNA sequencing. How do these additional electrodes affect the current distribution in the cell and hence the sensor performance? This is significantly less clear and thus in focus here. We use impedance modeling of a prototypical three-electrode nanopore sensor and show that, depending on the conditions, standard experimental device characterization is severely affected by the presence of the third electrode. On the other hand, the simulations also provide guidelines on how to avoid such complications, identify "safe" operating conditions, and design criteria for optimized nanopore sensors.