Fabrication of Graphene Nanopores and a Preliminary Study on λ-DNA Translocation

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 lambda-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 am 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 x 10(5)similar to 5 x 10(5) A/m(2) current density for 2 similar to 3 min The edges of these graphene nanopores became smoother and sharper when the temperature was increased to about 450 degrees C, 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.