Surface-charge induced ion depletion and sample stacking near single nanopores in microfluidic devices.

We report integrated nanopore/microchannel devices in which single nanopores are isolated between two microfluidic channels. The devices were formed by sandwiching track-etched conical nanopores in a poly(ethylene terephthalate) membrane between two poly(dimethylsiloxane) microchannels. Integration of the nanopores into microfluidic devices improves mass transport to the nanopore and allows easy coupling of applied potentials. Electrical and optical characterization of these individual nanopores suggests double layer overlap is not required to form an ion depletion region adjacent to the nanopore in the microchannel; rather, excess surface charge in the nanopore contributes to the formation of this ion depletion region. We used fluorescent probes to optically map the ion depletion region and the stacking of fluorescein near the nanopore/microchannel junction, and current measurements confirmed formation of the ion depletion region.