DNA compaction and dynamic observation in a nanopore gated sub-attoliter silicon nanocavity

Confinement of biopolymers inside volumes with micro- or nanoscale lateral dimensions is ubiquitous in nature. Investigating the behavior of biopolymers in a confined environment is essential to improve our basic understanding in life sciences. In this work, we present a nanopore gated sub-attoliter silicon nanocavity device, which allows DNA compaction similar to that in virus capsids. Single DNA molecules can be electrically driven into the nanocavity, and then get compacted inside the nanocavity under certain conditions. The dynamic fluctuations of the compacted DNA can be monitored via ionic current measurements. The mechanism for the DNA compaction is elucidated by varying the DNA length or concentration, voltage polarity, nanocavity dimensions and ionic strength. Furthermore, Brownian dynamics simulations reveal the dynamic fluctuations of the compacted DNA, which are reflected in the measured ionic current. Our nanocavity device is anticipated to provide a controlled environment in extremely small volumes for investigating the physics of confined biopolymers.

Controlled Focused Ion Beam Milling of Composite Solid State Nanopore Arrays for Molecule Sensing

Various nanoscale fabrication techniques are elaborated to form artificial nanoporous/nanochannel membranes to be applied for biosensing: one of the most prevalent is the micro-electromechanical systems (MEMS) compatible focused ion beam (FIB) milling. This technique can be easily adopted in micro- and nanomachining process sequences to develop composite multi-pore structures, although its precision and reproducibility are key points in the case of these thick multi-layered membranes. This work is to demonstrate a comprehensive characterisation of FIB milling to improve the reliability of the fabrication of solid state nanopore arrays with precisely predetermined pore geometries for a targeted molecule type to be recognised. The statistical geometric features of the fabricated nanopores were recorded as the function of the process parameters, and the resulting geometries were analysed in detail by high resolution scanning electron microscope (SEM), transmission electron microscope (TEM) and ion scanning microscopy. Continuous function of the pore diameter evolution rate was derived from the experimental results in the case of different material structures, and compared to former dissentient estimations. The additional metal layer was deposited onto the backside of the membrane and grounded during the ion milling to prevent the electrical charging of dielectric layers. The study proved that the conformity of the pore geometry and the reliability of their fabrication could be improved significantly. The applicability of the developed nanopore arrays for molecule detection was also considered by characterising the pore diameter dependent sensitivity of the membrane impedance modulation based measurement method.