In a recent publication in Nature Nanotechnology, Prof. Craig Martens of the UCI Chemistry Department, Prof. Zuzanna Siwy of the UCI Physics Department, and coworkers show how to induce current oscillations in a single nanopore [Nature Nanotechnology 3, 51 - 57 (2008)]. In strongly soluble salt solutions these systems act as molecular current rectifiers. When traces of sparingly soluble species, such as CaHPO4 are present, the systems undergo an intriguing transformation from DC current flow (a) to quasiperiodic current oscillations (b) when a critical membrane voltage is reached. This transition corresponds to negative differential resistance on the current-voltage (I-V) curve. The authors show how voltage-induced precipitation and re-dissolution inside the nanopore underlie the ion current oscillations. The behavior of these nonlinear systems is very sensitive to experimental conditions. The frequency of oscillation is tunable from a fraction of Hz to tens of Hz. The authors also discuss possible application of these nonlinear oscillating systems to the building a single pore-based chemical sensor.
Monday, February 18, 2008