Tuning interactions in nanopore arrays with charges on the pore walls

Abstract

Physiological processes at the cellular level are regulated by nanoconfined ionic transport. Protein channels regulate the passage of specific ions into and out of the cell, and biological systems rely on the concerted function of many channels embedded in their membranes. For instance, the propagation of an action potential down an axon is moderated by the coordinated transport of sodium and potassium ions across neuronal membranes. Beyond its ubiquity in biological systems, transport across nanoporous devices has industrial applications such as single-molecule sensing, energy storage, and water desalination. While single nanopore systems have been thoroughly studied in both biological and industrial contexts, systems containing an array of multiple nanopores are of increasing interest. Due to the close proximity of channels in an array, local environmental changes at the interface of one channel may influence the transport properties of neighboring channels. In this work, we fabricated nanopore arrays with tunable geometries and surface chemistries to probe this cross-talk between nanopores. We employed electron beam sculpting of silicon nitride membranes to fabricate arrays containing two and three nanopores. This method allowed us to engineer devices of varying interpore distances to probe neighboring interactions as a function of interpore distance. Using electrochemical methods, we characterized the current-voltage response of each array at varying sizes of the electric double layer to probe the nature of interpore interactions. Furthermore, we explored surface modifications to create nanopores with bipolar surface charge distributions, which effectively act as ionic diodes. Our results are also complemented by computational modeling. An exploration of the electrokinetic phenomena of these arrays will deepen our understanding of the interplay between neighboring channels, elucidating the mechanisms behind ionic sieving on the scale of an entire network of nanopores.