Molecular Dynamics Investigation of Water Behavior Through Nanopores

The transport of fluids through nanoscale pores, channels, and membranes has been of great importance in our daily life. Nanoscale transport is relevant to many applications such as agriculture, energy and environmental fields. Considering these applications, it is important to characterize detailed mechanisms of liquid transport through nanoscale defects and pores on surfaces. Such characterization requires a detailed understanding of the deviation of water behavior and its transport mechanisms in nanoscale from bulk water. Molecular dynamics provide proper means to understand the dynamics and mechanisms of motions of water molecules confined in ultra-small spaces. This work examines the water transport through an individual pore which has a nanoscale dimensions ranging from 1.0 to 1.8 nm from molecular dynamics perspective. The effects of the nanopore dimensions as well as the surface wetting properties on the behavior of confined water are studied. The translational and rotational dynamics of water molecules are characterized by examining velocity autocorrelation functions and the calculation of the density of states, which supports the presence of unusual, solid-like behaviors of water molecules. A good understanding of the transport mechanisms and their origins are crucial to address common challenges in many engineering applications such as energy storage and conversion and could pave the way towards more efficient water-energy systems.

Surface-state Coulomb repulsion accelerates a metal-insulator transition in topological semimetal nanofilms

The emergence of quantization at the nanoscale, the quantum size effect (QSE), allows flexible control of matter and is a rich source of advanced functionalities. A QSE-induced transition into an insulating phase in semimetallic nanofilms was predicted for bismuth a half-century ago and has regained new interest with regard to its surface states exhibiting nontrivial electronic topology. Here, we reveal an unexpected mechanism of the transition by high-resolution angle-resolved photoelectron spectroscopy combined with theoretical calculations. Anomalous evolution and degeneracy of quantized energy levels indicate that increased Coulomb repulsion from the surface states deforms a quantum confinement potential with decreasing thickness. The potential deformation strongly modulates spatial distributions of quantized wave functions, which leads to acceleration of the transition beyond the original QSE picture. This discovery establishes a complete picture of the long-discussed transition and highlights a new class of size effects dominating nanoscale transport in systems with metallic surface states.

Deconvolution of electroosmotic flow in hysteresis ion transport through single asymmetric nanopipettes

This report establishes a universal method to diagnose and deconvolute electroosmotic flow in nanoscale transport processes through current–potential measurements and analysis without simulation.

Active DNA unwinding and transport by a membrane-adapted helicase nanopore

Nanoscale transport through nanopores and live-cell membranes plays a vital role in both key biological processes as well as biosensing and DNA sequencing. Active translocation of DNA through these nanopores usually needs enzyme assistance. Here we present a nanopore derived from truncated helicase E1 of bovine papillomavirus (BPV) with a lumen diameter of c.a. 1.3 nm. Cryogenic electron microscopy (cryo-EM) imaging and single channel recording confirm its insertion into planar lipid bilayer (BLM). The helicase nanopore in BLM allows the passive single-stranded DNA (ssDNA) transport and retains the helicase activity in vitro. Furthermore, we incorporate this helicase nanopore into the live cell membrane of HEK293T cells, and monitor the ssDNA delivery into the cell real-time at single molecule level. This type of nanopore is expected to provide an interesting tool to study the biophysics of biomotors in vitro, with potential applications in biosensing, drug delivery and real-time single cell analysis.