Narrow Results

We study the distribution of ions and water within a pore in a polarizable membrane, in the presence of a stiff polyelectrolyte threaded through the pore. In this system, which represents a typical situation during the translocation of DNA, the distribution of both the ions and the water molecules is affected by the induced charges on the surface of the polarizable nanopore. Specifically, the concentration of counterions is enhanced near the surface of the pore, due to the attractive interaction with the induced charges. Conversely, the water within the pore is depleted, as a result of the disruption of hydrogen bonds by the induced charges.

We investigate the ejection dynamics of a flexible polymer chain out of confined environment by means of scaling considerations and Monte Carlo simulations. Situations of this kind arise in different physical contexts, including a flexible synthetic polymer partially confined in a nanopore and a viral genome partially ejected from its capsid. In the case of cylindric confinement the entropic driving force which pulls the chain out of the pore is argued to be constant once a few persistent lengths are out of the pore. We demonstrate that in this case the ejection dynamics follows a -law with elapsed time t. The mean ejection time τ depends nonmonotonically on chain length N. However, if the geometric constraints comprise a wider capsid chamber attached to a narrow exit tube, the mechanism of ejection changes and involves the surmounting of an activation barrier. The driving force then varies in time. One finds good agreement of theory and computer simulation with recent experiments with DNA.

A controlled electrical breakdown is used to produce efficient nanopore (NP) sensors. This phenomenon can be used to precisely fabricate these nanopore (NP) sensors through the membranes of the polydimethylsiloxane microarrays. This can be carried out, when localizing the electrical potential through a suitable microfluidic channel. Organic molecules, and other different protein-molecules, can be easily and precisely detected using this procedure referred to as controlled electrical breakdown technique.

The transport of biomolecules across bio-membranes occurs in a complex environment where the fluid on both sides of the membrane contains many inclusions. The Monte Carlo method and the hard-sphere (HS) model are used to simulate the translocation of linear polymer and ring polymer through a nanopore in a crowded environment. We compare the results of linear polymer and ring polymer and find that the ring polymer is more sensitive to the surrounding environment. Moreover, the influences of the nanopore and the inclusions to the translocation are studied and our results show that the nanopore changes the translocation time and the inclusions change the translocation tendency to the random side of the membrane. Here, the radius of gyration is described as a balance.

In this article we review recent developments in molecular transport and fluidics in carbon nanotube (CNT)-based nanochannels. Atomic molecular dynamics simulations and theoretical studies based on Fokker–Planck diffusion equation on the transport of large and long polymer molecules in CNTs are the focus of the article. Fast translocation and diffusion processes of large molecules in CNTs are reviewed and discussed, considering the effects of interfacial interactions and molecular conformations and structures at interface. The transport features for multiple molecules diffusing through CNTs are also discussed.

Separation of biomolecules based on their size and charge is an important procedure employed in biomolecular analysis. Nanosieve comprising of a semi-permeable membrane with nanometer-sized pores is used for this purpose. Described here is the fabrication of ultra thin nanoporous silicon membrane, which can be used as nanosieve, making use of standard microelectronics fabrication techniques. Lithography and bulk silicon etching is used to initially create a 10 μm thick sacrificial membrane in the center of a 200 μm thick silicon substrate. A three-layer stack of SiO₂, amorphous silicon (a-Si) and SiO₂ is then deposited using chemical vapor deposition technique. The sample is subjected to rapid thermal annealing during which pores are formed in the a-Si layer. Finally, the 15 nm thick nanoporous silicon membrane is released using reactive ion etching of the sacrificial membrane. The formation of the pores is confirmed by transmission and scanning electron microscope images. At present the pore formation is random; our future work will focus on controlled nucleation of silicon nanocrystals so as to get pores at desired locations.

Naturally derived biopolymers have been widely used for biomedical applications such as drug carriers, wound dressings, and tissue engineering scaffolds. Chitosan is a typical polysaccharide of great interest due to its biocompatibility and film-formability. Chitosan membranes with controllable porous structures also have significant potential in membrane chromatography. Thus, the processing of membranes with porous nanoscale structures is of great importance, but it is also challenging and this has limited the application of these membranes to date. In this study, with the aid of a carefully selected surfactant, polyethyleneglycol stearate-40, chitosan membranes with a well controlled nanoscale structure were successfully prepared. Additional control over the membrane structure was obtained by exposing the suspension to high intensity, low frequency ultrasound. It was found that the concentration of chitosan/surfactant ratio and the ultrasound exposure conditions affect the structural features of the membranes. The stability of nanopores in the membrane was improved by intensive ultrasonication. Furthermore, the stability of the blended suspensions and the intermolecular interactions between chitosan and the surfactant were investigated using scanning electron microscope and Fourier transform infrared spectroscopy (FTIR) analysis, respectively. Hydrogen bonds and possible reaction sites for molecular interactions in the two polymers were also confirmed by FTIR analysis.

Graphene is one of the most attractive two-dimensional materials that can be used for efficient desalination due to its ideal physical properties and high performance in ion selectivity and salt rejection. Here, in this paper, molecular dynamics simulations were applied to investigate the possibility of using a parallel nanopore system to pump ions so that the ions of both cation and anion species in the middle compartment could be evacuated at an extremely rapid rate. By building hexagonal parallel single-layer graphene films with spacing of 3.0 nm and changing the pore numbers and surface charge densities of the nanopores, the efficiency of desalination could be well controlled. It is found that the ion concentration decreases exponentially with time. The more the number of nanopore is, the stronger the surface charge density of nanopore is, the evacuation of ions in the middle compartment is more obvious, offering a new means for controlling the desalination efficiency. The simulations performed here provide theoretical insights for designing and fabricating high efficient and less energy consumption graphene desalination devices in the future.

In this paper, Nano-fluid loss additive was synthesized and characterized using Transmission Electron Microscopy (TEM) and the particle size analyzer. The TEM results have shown the formation of microspheres and the linkage of molecular polymer chains with hydrogen and ionic bonding. Particle size analysis indicated the presence of flexible Nano material in water and the stability of the Nano material in drilling fluid. The fluid property tests demonstrated that the filtration of Nano polymer was fairly good with the usage of common fluid loss agent. In addition, there was only a small change of filtration volumes before and after the administering of the aging test at 180°C, indicating high thermal stability.

With the development of science and technology, much more aspects of nano-technology have been used for studying macrobiomolecules, but seldom for single-molecular detection (SMD).We reviews recent results in the research of DNA molecules with nanopores, introduce basic concept and technology which can be used to study the disassembling dynamics of nucleosomes. We present here that the two transport parameters of blockade current and duration yield the sequence and the structural information of the collagen-like peptides and α-helix peptides. As the nanopore is the only channel the conducts ions, when the large biomolecules is being translocated through the pore under the applied electric field, a passing ion current blockade will be observed, which is based on the relationship of the protein's conformation feature with the change of ion current parameters. Nanopore analysis clearly showed the blockade current and duration is related to the tertiary structures of peptides. The new method could be possible to develop a highly sensitive analysis for the conformation change of protein related to human disease.