Papers by Keyword: Nanopore

Abstract: This report studies the charge-based sensing modality of FET-embedded nanopore biosensors through FEM simulation. PNP equation is solved to analyze the mirror charge introduced by charged biomolecule while threading through the nanopore-FET sensor. Negative and positive charged molecules are analyzed respectively. Obvious local potential change induced by the presenting of charged molecules nearby is observed. In addition, the transport-induced descreening effect is observed under intensive bias, which might explain the capability of charge sensing even under high concentrations such as 1 M for FET-nanopore biosensors.

Abstract: Graphene nanopore has been widely employed in nanofilter or nanopore devices due to its outstanding properties. The understanding of its mechanical properties at nanoscale is crucial for device improvement. In this work, the mechanical properties of graphene nanopore is thus investigated using atomistic finite element method (AFEM). Four graphene models with different pore shapes (circular (CR), horizontal rectangle (RH), and vertical rectangle (RV)) in sub-nm size which could be successfully fabricated experimentally have been studied here. The force normal to a pore surface is applied to mimic the impact force due to a fluid flow. Increasing pore size results in the reduction in its strength. Comparing among different pore shapes with comparable sizes, the order of pore strength is CR>RH>RV>SQ. In addition, we observe that the direction of pore alignment and geometries of pore edge also play a key role in mechanical strength of nanopores.

Abstract: In this paper, the nano flexible polymer was synthesized and the plugging property of the polymer in the drilling fluid was studied. The characterization and properties of nano flexible polymer were invested by Particle Size Analyzer and Transmission Electron Microscopy. The nano flexible polymer was synthesized successfully and it was flexible nano material both in water and in drilling fluid. The filtration ability of the polymer was studied by drilling fluid filter press and the results indicated that the filtration property was equal to commonly used fluid loss agent in drilling fluid. The plugging ability was studied by specific surface and porosity physical adsorption instrument (BET). The surface area reduced after treated with the polymer, indicating the nano flexible polymer entered into nanopores of shale formation due to the adsorption in the surface of shale. It was further exhibited that nanopores of shale were plugged by the nano flexible polymer.

Abstract: As the single molecules detection tool, nanopore is applied in more and more fields, such as medicine controlled delivery, ion conductance microscopes, nanosensors and DNA sequencing. When molecules pass through a nanopore, they will physically block the pore and produce measurable changes in ionic currents under an external electrical potential. Based on analyzing the resultant electrical signals, it is possible to detect various bio-molecules.Generally, the capturing ratio of nanopre for molecules is dependent on the intensity of electrical potential, to which the duration time of event is inversely proportional. It is difficult to analyze the too short duration time. Therefore, we investigate the study on concentration gradient of ionic solution effect on the capturing ratio of nanopore for DNA, which is in order to get the higher capturing ratio with the invariant duration time.In the experiments, we add different concentration solution in trans and cis parts of naopore separately to form the concentration gradient. We use three different types nanopore (α-hemolysin nanopore, Si3N4 membrane nanopore, glass capillary nanopore) to compare and get the similar results. The events of DNA translocating through nanopore are observed more compressed during the fixed time under the higher concentration gradient and there is no change to the duration time of DNA passing through the nanopore. It is demonstrated that concentration gradient could increase the capturing ratio of nanopore for DNA.

Abstract: Nanopore based sensors have been widely spread utilized for detection and analysis of various single charged molecules. However, collision and trap events also block the ionic current that interferes recording the actually translocation events. In order to resolve the problem, we propose inducing a salt gradient to turn the pulse form negative to positive. And the salt gradients dependence of pulse signals ranging from 1 M (cis & trans) to 1 M (cis) - 4 M (trans) is mapped. Experiment results demonstrate that applying a high salt gradient prolong translocation time 1.5 times and increase molecule capture rate by a fact of 3. It is benefit for nanopore further application.

Abstract: The use of anodized aluminum oxide (AAO) is vastly being explored in recent years. The application includes molecular separation, sensing, energy storage and template synthesis for various nanostructures. The reason AAO is preferred was because of the ability to control the nanopore structure by manipulating some factors during the anodisation process. This study will investigate the exploitation of voltage and anodisation time during the anodisation process and the effect it has on the nanopore structure of the AAO by examining the structure under Field Emission Scanning Electron Microscope (FE-SEM). The experiment was carried out by anodizing aluminum foil in 0.3 M oxalic acid as electrolyte under the constant temperature of 5 °C. The applied voltage was varied from 40, 60 and 100 V with different anodisation time. The outcome of this study demonstrates that applied voltage has a proportional relationship with the developed pore size. Increasing the applied voltage from 40 to 100 V had increased the pore size of the AAO from 38 nm to 186 nm, respectively. Aluminium oxide anodized at 60 V demonstrates pore size in the range of 76 nm. Prolong anodisation time had improved the pore morphology of anodized aluminium oxide in the case of 40 V, however, the pore wall starts to collapse when anodisation time is more than 4 minutes at 100 V.

Abstract: Although nanoimprint lithography (NIL) can successfully fabricate structures down to 10 nm [1], it is difficult to produce perforated pores with diameters less than 100 nm in freestanding polymer membranes. Since it requires molding using a stamp with extremely high aspect ratio to achieve high mechanical stability for the membrane fully released from a substrate. We utilized silicon microneedle structures as an imprinting mold that overcomes these issues. Also, pressed self-perfection (PSP) process was employed after nanoimprinting to further reduce the pore size. Additionally, the membranes were integrated with microfluidic devices to measure current-voltage curves in order to determine pore size indirectly.

Abstract: The flow pattern is unique in a certain range of pore size divided by the Knudsen number. In order to characterize permeability of nanopore in shale gas reservoir more accurately, the formulas of nanopore permeability are put forward considering the influence of adsorption gas and flow patterns. After the calculated results were compared and analyzed, the conclusions are obtained as follows: (1) Pore size is the main factor to determine the flow pattern; (2) There are three main flow pattern in the nanopore of Longmaxi formation shale reservoirs, slip flow, Fick diffusion and transition diffusion, meanwhile Darcy percolation and Knudsen diffusion do not exist; (3) Flow pattern has great influence on apparent permeability and adsorption has a greater impact in a high pressure condition (greater than 20MPa).

Abstract: With the miniaturization of the NEMS/MEMS, the size effect becomes significant in the nanochannels/nanopores through which fluid flows as well as the interface effect. By all-atom molecular dynamics (MD) simulations, the ion transportation is investigated in nanopores as well as the physical properties at solid-liquid interface. To describe the anion and cation distributions of NaCl solution in vicinity of graphene nanopores, a new MD model was developed, taking thermal vibration of wall atoms, the structure of solvent molecules and ion sizes into consideration. The main peak locations of ion distributions stayed unchanged by changing the nanopore size, the solution concentration and the electric field strength. The ionic currents increased linearly with the diameter and the electric field strength, while it increased non-linearly with the solution concentration.

Abstract: While the flow rates (in unit of particles/s) of the ions in aqueous solution depend on the cross sections of the channels they pass through, the flux (in unit of particles/(m²s)) is usually independent of them. However, if the diameter of the channel becomes extremely small and comparable to the effective size of the ions, there can be the dependence of the flux on the channel diameter. The finite size effect of solute ions through such small channel is relevant to the physical process of other nanofluidic technologies such as the DNA translocation through nanopore for the sequencing technologies. In this study, we examine the flow of K⁺ and Cl^- ions in water through nanopores made of graphene structure by molecular dynamics method. The results show that there is a transition of zero to nonzero flux when the pore diameter is around the effective size of the ions. Furthermore, there is a dependence of the flux on the nanopore diameter around this regime.