Single-walled carbon nanotubes (SWCNTs) have attracted great attention on account of their superior and tunable electrical properties for promising applications in low-cost and high-performance nano-electronics and thin-film devices.

In this work, we demonstrate a chemical modification approach, by means of covalent-bonding amphoteric poly- l -lysine (PLL) on the interior nanopore surface, which could intensively protect the pore from etching when exposed in the electrolyte under various pH conditions (from pH 4 to 12). Nanopore was generated via simple current dielectric breakdown methodology, covalent modification was performed in three steps, and the functional nanopore was fully characterized in terms of chemical structure, hydrophilicity, and surface morphology. I – V curves were recorded under a broad range of pH stimuli to evaluate the stability of the chemical bonding layer; the plotted curves demonstrated that nanopore with a covalent bonding layer has good pH tolerance and showed apparent reversibility. In addition, we have also measured the conductance of modified nanopore with varied KCl concentration (from 0.1 mM to 1 M) at different pH conditions (pHs 5, 7, 9, and 11). The results suggested that the surface charge density does not fluctuate with variation in salt concentration, which inferred that the SiN x nanopore was fully covered by PLL. Moreover, the PLL functionalized nanopore has realized the detection of single-stranded DNA homopolymer translocation under bias voltage of 500 mV, and the 20 nt homopolymers could be evidently differentiated in terms of the current amplitude and dwell time at pHs 5, 8, and 11.

The fabrication of nanopores through a dielectric breakdown method, achieved by simple, low-cost desktop setups, has promoted the research of solid-state nanopore sensing. This paper reports a method for fabricating nanopores. This method uses transient high electric field controlled breakdown (THCBD) to form electric-field-dependent nanopores with different diameters in the order of milliseconds. By manipulating a micropipette with a high electric field to establish the meniscus contact with the SiN x membrane, nanopores can be formed through an “auto-brake” fabrication process. Compared with the traditional dielectric breakdown, THCBD can greatly shorten the breakdown time and form pores of different sizes under higher electric fields without causing additional damage to the SiN x membrane. The nanopores formed by this method can be successfully used to detect two types of RNA molecules. One is transfer RNA from yeast extract and the other is a synthetic RNA oligonucleotide fragment (rArArArArArArArArArArArA).