Ionic current modulation from DNA translocation through nanopores under high ionic strength and concentration gradients

Abstract

Ion transport through nanopores is an important process in nature and has important engineering applications. To date, most studies of nanopore ion transport have been carried out with electrolytes of relatively low concentrations. In this paper, we report on ionic current modulation from the translocation of dsDNA through a nanopore under high ionic strength and with an electrolyte concentration gradient across the nanopore. Results show that in this case, DNA translocation can induce either negative or positive ionic current modulation, even though usually only downward peaks are expected under this high ion concentration. Through a series of experiments and numerical simulations with nanopores of different diameters and concentration gradients, it is found that the positive pulse is due to extra ions outside the electric double layer of the DNA that are brought into the nanopore by the enhanced electroosmotic flow (EOF) with the negatively charged DNA inside the nanopore.

The Origin of Conductive-Pulse Sensing Inside a Nanopore and the Role of Electro-Hydrodynamics

“…To show that this nding is not limited to low ionic strength phenomenon, we employed salt concentration gradients as previously described 20 . As shown in Figure 1e, our experimental set-up involved having a solution of 1 M KCl + λ-DNA inside the nanopore with 4 M KCl outside.…”

“…Although these hypotheses can predict the well-known crossover point in which events transition from resistive to conductive (via decreasing salt concentrations), the cation-speci c, voltage-speci c, and pore size-speci c dependence of CEs have not been studied and should provide con rming evidence for one of these hypotheses 6,19 . One recent experiment in particular con icts with these hypotheses and may lead to a third potential theory; namely that current enhancement is not only a low salt phenomena and can also be observed at high, asymmetric salt conditions 20 . Above 1 M KCl, counterions should contribute very little to current modulation.…”

Salt Gradient Modulation of MicroRNA Translocation through a Biological Nanopore

“…The authors postulated that salt gradients enhance the electric funneling field near the pore entrance, and also increase the electro-osmotic counterflow inside the pore, 22 which was later supported by a number of comprehensive theoretical studies on KCl salt gradients over solid-state nanopores. [23][24][25][26][27][28][29][30][31][32] Kowalczyk et al also investigated alternative electrolyte species, concluding that DNA dwell times in a silicon nitride pore increase when symmetrical KCl is replaced with NaCl or LiCl because of stronger DNA binding of these smaller cations. 33…”

On the Origins of Conductive-Pulse Sensing Inside a Nanopore

“…To show that this finding is not limited to low ionic strength phenomenon, we employed salt concentration gradients as previously described 20 . As shown in Figure 1e, our experimental set-up involved having a solution of 1 M KCl + λ -DNA inside the nanopore with 4 M KCl outside.…”