Physical origin of dynamic ion transport features through single conical nanopores at different bias frequencies

Abstract

Ionic transport through nanometer scale channels or interfaces is the physical origin of the detection signals in stochastic single molecular sensing, DNA sequencing and nano-structured electrodes. Dynamic transport regulated by systematically varying the bias frequency has not been explored. In this report, ion transport through single conical nanopore platforms is studied by applying an alternating electrical field at a wide range of scan rates. Rich frequency-dependent features of the measured transport current are discovered. The complete transition of characteristic transport features from low to high scan rates or bias frequencies is demonstrated experimentally. Key dynamic features include: multiple hysteresis loops separated by one or two non-zero cross points in the I–V curves, shifts in cross point potentials at different scan rates, and growth and diminishment in the hysteresis loops with normal and negative phase shifts. Combined theoretical and experimental studies reveal different processes contributing to and dominating the total current responses on different time scales. The respective contributions of each type of transport process to the overall measured current signals are quantitatively separated based on the fundamental insights gained. Although these exciting experimental observations are successfully simulated using an optimized model by solving PNP equations, the experimental studies at this nanoscale dimension suggest substantial deviations from a continuum regime. Inputs from molecular theory are needed to further validate the proposed physical mechanism.