The ability to create solid-state materials at the nanoscale is important for the development of many nanoscale sensor devices, and in particular, solid-state nanopore sensors. Nanopore sensors are used to sense various types of biomolecules and small molecular complexes by applying a voltage across a nanopore and measuring the flux of ions that cross the pore as a function of time.

Meni Wanunu, Northeastern University, Boston, MA, USA, and colleagues have used a laser-induced thinning approach on silicon nitride (SiNx) membranes to form asymmetric nanopores. The researchers first grew the silicon nitride using deposition and reactive ion etching (RIE) methods. The membranes were then cleaned using oxygen plasma treatment, followed by wet chemical methods. The membranes were then thinned using a laser and an electrokinetic dielectric breakdown method to create the nanopores.

The researchers found that the silicon nitride membranes can be etched using laser light. By combining this approach with the dielectric breakdown method, they could create nanopores with dimensions of 1–2 nm. The pore geometries using this approach are more akin to a funnel rather than the conventional hourglass shape, and could be used to discriminate between different DNA lengths and detect DNA homopolymer sequences. This could broaden the range of applications where nanopores are used, with potential examples in biopolymer sequencing and in the detection of specific biomarkers.

• Photothermally Assisted Thinning of Silicon Nitride Membranes for Ultrathin Asymmetric Nanopores,
  Hirohito Yamazaki, Rui Hu, Qing Zhao, Meni Wanunu,
  ACS Nano 2018.
  https://doi.org/10.1021/acsnano.8b06805