We report on DNA translocations through nanopores created in graphene membranes. Devices consist of 1-5 nm thick graphene membranes with electron-beam sculpted nanopores from 5 to 10 nm in diameter. Due to the thin nature of the graphene membranes, we observe larger blocked currents than for traditional solid-state nanopores. However, ionic current noise levels are several orders of magnitude larger than those for silicon nitride nanopores. These fluctuations are reduced with the atomic-layer deposition of 5 nm of titanium dioxide over the device. Unlike traditional solid-state nanopore materials that are insulating, graphene is an excellent electrical conductor. Use of graphene as a membrane material opens the door to a new class of nanopore devices in which electronic sensing and control are performed directly at the pore.

Nanopore-based DNA analysis is a new single-molecule technique that involves monitoring the flow of ions through a narrow pore, and detecting changes in this flow as DNA molecules also pass through the pore. It has the potential to carry out a range of laboratory and medical DNA analyses, orders of magnitude faster than current methods. Initial experiments used a protein channel for its pre-defined, precise structure, but since then several approaches for the fabrication of solid-state pores have been developed. These aim to match the capabilities of biochannels, while also providing increased durability, control over pore geometry and compatibility with semiconductor and microfluidics fabrication techniques. This review summarizes each solid-state nanopore fabrication technique reported to date, and compares their advantages and disadvantages. Methods and applications for nanopore surface modification are also presented, followed by a discussion of approaches used to measure pore size, geometry and surface properties. The review concludes with an outlook on the future of solid-state nanopores.

We observe single nanoparticle translocation events via resistive pulse sensing using silicon nitride pores described by a range of lengths and diameters. Pores are prepared by focused ion beam milling in 50 nm-, 100 nm-, and 500 nm-thick silicon nitride membranes with diameters fabricated to accommodate spherical silica nanoparticles with sizes chosen to mimic that of virus particles. In this manner, we are able to characterize the role of pore geometry in three key components of the detection scheme, namely, event magnitude, event duration, and event frequency. We find that the electric field created by the applied voltage and the pore's geometry is a critical factor. We develop approximations to describe this field, which are verified with computer simulations, and interactions between particles and this field. In so doing, we formulate what we believe to be the first approximation for the magnitude of ionic current blockage that explicitly addresses the invariance of access resistance of solid-state pores during particle translocation. These approximations also provide a suitable foundation for estimating the zeta potential of the particles and/or pore surface when studied in conjunction with event durations. We also verify that translocation achieved by electro-osmostic transport is an effective means of slowing translocation velocities of highly charged particles without compromising particle capture rate as compared to more traditional approaches based on electrophoretic transport.