Fabrication of Graphene Nanopores and a Preliminary Study onλ-DNA Translocation

Abstract

Nanopore sequencing is among the most promising technologies to achieve the goals of the "$1,000 Genome." Two major types of nanopores have been extensively investigated, protein and silicon-based solid-state nanopores. However, protein pores are short-lived and the length of solid-state nanopores is much larger than the distance between adjacent bases, resulting in incapability to discriminate individual bases along the single-stranded DNA molecules. In this paper, we report λ-DNA translocations through graphene nanopore. A large nanopore with diameter of about 30 nm on silicon nitride substrates were first fabricated using focused ion beam(FIB) system under the beam current of 2 pA, accelerating voltage of 30 kV and sculpting time of 1 s. Individual graphene membranes were suspended onto the substrates to cover the large pore, and nanopores with a diameter less than 10 nm are sculpted in the graphene sheet by focused electron beam(FEB) from a transmission electron microscope(TEM) under a 400 kx magnification times and 300 kV accelerating voltage at 1×105~5×105A/m2 current density for 2~3 min. The edges of these graphene nanopores became smoother and sharper when the temperature was increased to about 450 ℃, which might help to lower interactions between graphene nanopores and the analytes. The signals of DNA translocation through graphene nanopores had been recorded using a patch clamp amplifier at 10 kHz sampling frequency filtered at 5 kHz via an integrated four-pole low-pass Bessel filter. Analyses of the DNA translocation current traces indicated that different conformations of DNA molecules may exist during entrance into nanopores. In addition, our overall detection platform had a low noise amplitude of around 10 pA, which allowed more sensitive signal detection. Taken together, our observations demonstrate that graphene nanopores are feasible for DNA sensing, leading a forward step towards single-molecule DNA sequencing using monolayered graphene nanopores.