Kinetics of nanopore fabrication during controlled breakdown of dielectric membranes in solution

Abstract

Nanopore fabrication by controlled breakdown (CBD) overcomes many of the challenges of traditional nanofabrication techniques, by reliably forming solid-state nanopores sub-2 nm in size in a low-cost and scalable way for nucleic acid analysis applications. Herein, the breakdown kinetics of thin dielectric membranes immersed in a liquid environment are investigated in order to gain deeper insights into the mechanism of solid-state nanopore formation by high electric fields. For various fabrication conditions, we demonstrate that nanopore fabrication time is Weibull-distributed, in support of the hypothesis that the fabrication mechanism is a stochastic process governed by the probability of forming a connected path across the membrane (i.e. a weakest-link problem). Additionally, we explore the roles that various ions and solvents play in breakdown kinetics, revealing that asymmetric pH conditions across the membrane can significantly affect nanopore fabrication time for a given voltage polarity. These results, characterizing the stochasticity of the nanopore fabrication process and highlighting the parameters affecting it, should assist researchers interested in exploiting the potential of CBD for nanofluidic channel fabrication, while also offering guidance towards the conceivable manufacturing of solid-state nanopore-based technologies for DNA sequencing applications.

Solid-state nanopore localization by controlled breakdown of selectively thinned membranes

“…However, certain factors – including applied voltage, pH, membrane thickness and area – play a vital role in determining the most probable time to breakdown. [19,46] Given the exponential dependence of pore fabrication time on electric field strength, for a given applied voltage, locally thinning the membrane will produce a region where the electric field is proportionally stronger (Figure 1(c), inset diagrams), thus increasing the rate of defect generation per unit area in the thinned region compared to the rest of the membrane. In essence, the thinned region would offer a more favorable path toward pore formation than the thicker surrounding membrane for a given voltage.…”

“…[21] In addition, ion beam exposure is known to induce defects,[47] which may further contribute to pore formation efficiency. [48]…”

“…Some increase in pore fabrication time was expected, concurrent with the six-fold reduction in the area of the thinned region; strong area dependence of fabrication time by CBD is consistent with the Weibull distribution of nanopore fabrication time developed in previous work. [21] However, the six-fold reduction in area cannot account for the three orders of magnitude increase in pore fabrication time.…”

“…[19,21] Most standard nanopore-based sensors do not require pore positioning, but a number of specialized applications – including nanofluidic transistors, electrode-embedded devices,[23– 34] and plasmonic optical detection of analytes[35–38] – necessitate formation of the pore within a short distance of an existing structure on the membrane. Other applications require pore fabrication in a region of the membrane that has been locally thinned to maximize the signal amplitude of translocating biomolecules.…”

Detection of methylation on dsDNA using nanopores in a MoS2 membrane

“…47 Various strategies, from applying gel media on the cis or trans side of the membrane, to varying voltage or buffer solution concentration gradient, have been implemented to slow translocation and suspend DNA strands in the pore. 47–48 For our experiment, we used an asymmetric buffer solution of 0.6M KCl on the cis side of the membrane and 3M KCl on the trans side. Our MoS 2 nanopore-based methylation assay demonstrates detection of a single methylation CpG dyad site at the end of 90bp dsDNA.…”