Person:

Golovchenko, Jene

It has recently been recognized that solid-state nanopores in single-atomic-layer graphene membranes can be used to electronically detect and characterize single long charged polymer molecules. We have now fabricated nanopores in single-layer graphene that are closely matched to the diameter of a double-stranded DNA molecule. Ionic current signals during electrophoretically driven translocation of DNA through these nanopores were experimentally explored and theoretically modeled. Our experiments show that these nanopores have unusually high sensitivity (0.65 nA/Å) to extremely small changes in the translocating molecule’s outer diameter. Such atomically short graphene nanopores can also resolve nanoscale-spaced molecular structures along the length of a polymer, but do so with greatest sensitivity only when the pore and molecule diameters are closely matched. Modeling confirms that our most closely matched pores have an inherent resolution of ≤0.6 nm along the length of the molecule.

A variety of different DNA polymers were electrophoretically driven through the nanopore of an α-hemolysin channel in a lipid bilayer. Single-channel recording of the translocation duration and current flow during traversal of individual polynucleotides yielded a unique pattern of events for each of the several polymers tested. Statistical data derived from this pattern of events demonstrate that in several cases a nanopore can distinguish between polynucleotides of similar length and composition that differ only in sequence. Studies of temperature effects on the translocation process show that translocation duration scales as ∼T−2. A strong correlation exists between the temperature dependence of the event characteristics and the tendency of some polymers to form secondary structure. Because nanopores can rapidly discriminate and characterize unlabeled DNA molecules at low copy number, refinements of the experimental approach demonstrated here could eventually provide a low-cost high-throughput method of analyzing DNA polynucleotides.

Nanopores in graphenemembranes can potentially offer unprecedented spatial resolution for single molecule sensing, but their fabrication has thus far been difficult, poorly scalable, and prone to contamination. We demonstrate an in-situfabrication method that nucleates and controllably enlarges nanopores in electrolyte solution by applying ultra-short, high-voltage pulses across the graphenemembrane. This method can be used to rapidly produce graphenenanopores with subnanometer size accuracy in an apparatus free of nanoscale beams or tips.