A thorough understanding of nanoscale transport properties is vital for the development and optimization of nanopore sensors. The thickness of the electrical double layers (EDLs) at the internal walls of a nanopore, as well as the dimensions of the nanopore itself, plays a crucial role in determining transport properties. Herein, we demonstrate the effect of the electrolyte concentration, which is inversely proportional to the EDL thickness, and the effect of pore size, which controls the extent of the electrical double layer overlap, on the ion current rectification phenomenon observed for conical nanopores. Experimental and numerical results showed that as the electrolyte concentration is decreased, the rectification ratio reaches a maximum, then decreases, and eventually inverts below unity. We also show that as the pore size is decreased, the rectification maximum and the inversion take place at higher electrolyte concentrations. Numerical investigations revealed that both phenomena occur due to the shifting of ion enrichment distributions within the nanopore as the electrolyte concentration or the pore size is varied.

The α-hemolysin nanopore has attracted much attention as a tool for the singlemolecule analysis of DNA due to its potential as an ultra-sensitive, specific, and label-free sensing technique. The vast majority of DNA sensing research with the α-hemolysin nanopore has focused on interrogating single-stranded DNA. Nevertheless, the structure of the α-hemolysin pore, specifically the circa 32.6 cubic nanometer vestibule, is of sufficient size for a short section of double-stranded DNA (dsDNA) to reside before unzipping into its single-stranded constituents. In this review, we describe past and current literature relating to the rich information that can be obtained from the interrogation of dsDNA while residing within the α-hemolysin nanopore vestibule, and the subsequent voltage-driven unzipping of the residing DNA into its single-stranded constituents. Applications for dsDNA interrogation and unzipping that have been implemented include DNA sequencing, disease diagnosis, and the identification of epigenetic modifications.