Controlling nanopore size, shape and stability

Abstract

Solid-state nanopores are considered a promising tool for the study of biological polymers such as DNA and RNA, due largely to their flexibility in size, potential in device integration and robustness. Here, we show that the precise shape of small nanopores (∼5 nm diameter in 20 nm SiN membranes) can be controlled by using transmission electron microscope (TEM) beams of different sizes. However, when some of these small nanopores are immersed in an aqueous solution, their resistance is observed to decrease over time. By comparing nanopores of different shapes using (scanning) TEM both before and after immersion in aqueous solution, we demonstrate that the stability of small nanopores is related to their three-dimensional geometry, which depends on the TEM beam size employed during pore fabrication. Optimal stability is obtained using a TEM beam size of approximately the same size as the intended nanopore diameter. In addition, we show that thermal oxidation can serve as a means to independently control nanopore size following TEM fabrication. These observations provide key guidelines for the fabrication of stable solid-state nanopores on the scale of nucleic acids and small proteins.

Nano-structured interface of graphene and h-BN for sensing applications

“…There are enormous experimental efforts underway to control the pore size, shape and stability [16,17], and it can be said that nowadays it remains a significant technological challenge to build a sophisticated nano-biosensor.…”

“…Their controlled fabrication in solid-state materials still poses some challenges. In recent studies [16], nanopores were created on SiN membranes and it was claimed that it is possible to control the stability, size and also the shape of the nanopores, using transmission electron microscope (TEM). Another technique, using electrochemical reaction (ECR) [17], can create a nanopore in 2D materials with ann atom-by-atom control, and this technique has been applied on both graphene and MoS 2 .…”

Through a Window, Brightly: A Review of Selected Nanofabricated Thin-Film Platforms for Spectroscopy, Imaging, and Detection

“…[235][236][237] In overview, nanopores as small as 1 nm in diameter and $10 nm long can be fabricated with some flexibility in fabrication method. Characterization of nanopores can be done using chargedparticle microscopes and related techniques such as electron tomography and EELS, 219,220,[238][239][240][241] or by much less instrumentally intensive (ionic) conductance-based approaches.…”

Fine-tuning the Size and Minimizing the Noise of Solid-state Nanopores

“…Despite this limitation, the transition from one setup to the other is quick and straightforward. In comparison with existing techniques for controlling nanopore size such as the use of SEM 5 , thermal oxidation and membrane reshaping 8 , high electric fields offer a faster, more precise and less expensive methodology that can be performed on the lab bench using standard equipment and provide a broader range of nanopore sizes. The ability to rapidly and reproducibly reduce low-frequency noise also makes initial fabrication more reliable and prolongs the lifetime of solid-state nanopores, as previously used pores can be rejuvenated for further experiments.…”

“…For example, nanopores drilled by focused-ion beam have been recently shown to shrink under specific experimental conditions in a scanning electron microscope (SEM) 5 . In other approaches, nanopores drilled by transmission electron microscopy (TEM) can expand or shrink depending on the beam conditions and subsequent exposure to aqueous solvents 8 . In these cases, the achievable range of nanopore sizes is limited, difficult to control and even unreliable as the size of the nanopore can change following chemical treatment or when immersed in a particular liquid environment 9 .…”