Experiment and Simulation of Ion Transport through Nanopipettes of Well-Defined Conical Geometry

We describe simulated models combined with experimental results that investigate mechanisms of ion transport and current rectification in asymmetric nanochannels fabricated from quartz nanopipettes. Numerical simulation of a nanopipette model was performed through coupled Poisson-Nernst-Planck equations. Simulation results suggest the highest degree of rectification does not always appear at lowest electrolyte concentration. To support this model with experimental evidence, pipettes with various geometries were prepared and characterized with current-voltage measurements. Exact geometries of individual pipettes were obtained by scanning electron and scanning transmission microscopies. Current-voltage responses of pipettes with tip radii that varied from 14 nm to 3800 nm and cone angles that varied from 5.0° to 66° were measured as a function of electrolyte concentrations over the range of 1 mM to 1000 mM. These studies of ion transport mechanisms through nanopipettes provide a basis for applications of nanopipettes as delivery tools, separation devices or biosensors.