Controlling the ionic current rectification factor of a nanofluidic/microfluidic interface with symmetric nanocapillary interconnects.

The current rectification factor can be tailored by changing the degree of asymmetry between the fluid baths on opposite sides of a nanocapillary membrane (NCM). A symmetric device with symmetric fluid baths connected to opposite sides of the NCM did not rectify ionic current; while a NCM connected between fluid baths with a 32-fold difference in cross-sectional area produced a rectification factor of 75. The data suggests that the primary mechanism for the current rectification is the change in cross-sectional area of the fluid baths and the polarity dependent propagation of the enriched and depleted concentration polarization (CP) zones into these regions. An additional contribution to the increasing rectification factor with increasing bath asymmetry appears to be a result of electroconvection in the macropore, with inside diameters (IDs) of 625 and 850-μm. Power spectral density (PSD) analysis reveals chaotic oscillations that are consistent with electroconvection in the I-t data of the 625 and 850-μm ID macropore devices. In the ON state, current rectification keeps ionic transport toward the NCM high, increasing the speed of processes like sample enrichment. A simple means is provided to fabricate fluidic diodes with tailored current rectification factors.