Negative Mem-Capacitance and Warburg Ionic Filtering in Asymmetric Nanopores

Abstract

The pervasive model for a solvated, ion-filled nanopore is often a resistor in parallel with a capacitor. Although the simple model suggests that ionic current can flow through both components, under voltage-clamped conditions, capacitive currentshouldbe negligible. However, non-linear electrokinetics routinely predict voltage and capacitance fluctuations that can lead to otherwise anomalous current transients. We aimed to test the hypothesis that voltage and/or capacitance can fluctuate despite distant electrodes being clamped at a specified voltage. The first supportive piece of evidence for this theory is the appearance ofnegativecapacitance within the nanopore sensor which is characterized by long equilibration times and is observed only under millimolar salt concentrations. Next, we used the transient occlusion of the pore using λ-DNA and 10-kbp DNA to test whether events are being attenuated by this purely ionic phenomenon. We conclude the study with a new interpretation of molecular translocations which is not only based on the pulse-like resistance changes but rather a complex and non-linear pseudo-steady state that changes during molecular transit.