RESUMO
Nanopores attracted a great deal of scientific interest as templates for biological sensors as well as model systems to understand transport phenomena at the nanoscale. The experimental and theoretical analysis of nanopores has been so far focused on understanding the effect of the pore opening diameter on ionic transport. In this article we present systematic studies on the dependence of ion transport properties on the pore length. Particular attention was given to the effect of ion current rectification exhibited in conically shaped nanopores with homogeneous surface charges. We found that reducing the length of conically shaped nanopores significantly lowered their ability to rectify ion current. However, rectification properties of short pores can be enhanced by tailoring the surface charge and the shape of the narrow opening. Furthermore we analyzed the relationship of the rectification behavior and ion selectivity for different pore lengths. All simulations were performed using MsSimPore, a software package for solving the Poisson-Nernst-Planck (PNP) equations. It is based on a novel finite element solver and allows for simulations up to surface charge densities of -2 e per nm(2). MsSimPore is based on 1D reduction of the PNP model, but allows for a direct treatment of the pore with bulk electrolyte reservoirs, a feature which was previously used in higher dimensional models only. MsSimPore includes these reservoirs in the calculations, a property especially important for short pores, where the ionic concentrations and the electric potential vary strongly inside the pore as well as in the regions next to the pore entrance.
RESUMO
We have measured the flow of gas through single ion track pores in a polymer film using a mass spectroscopy technique. The pores are 12 µm long with diameters in the range of 50-1000 nm, and the flow was driven by pressure drops in the range 0-30 atm. When the mean free path is large compared to the pore diameter (large Knudsen number Kn), the flow rate is proportional to the pressure drop and the pore radius R cubed, and is consistent with a model of diffusive scattering at the pore walls. For Kn≤0.1, the hydrodynamic conductance increases, as predicted by standard kinetic theory models, and finally approaches the conventional Poiseuille value with zero slip length.
Assuntos
Biofísica/métodos , Espectrometria de Massas/métodos , Polímeros/química , Algoritmos , Difusão , Gases , Cinética , Microfluídica , Modelos Estatísticos , Modelos Teóricos , Nanotecnologia , Pressão , TemperaturaRESUMO
High surface charges of polymer pore walls and applied electric fields can lead to the formation and subsequent dissolution of precipitates in nanopores. These precipitates block the pore, leading to current fluctuations. We present an extended Poisson-Nernst-Planck system which includes chemical reactions of precipitation and dissolution. We discuss the mathematical modeling and present 2D numerical simulations.
Assuntos
Precipitação Química , Modelos Químicos , Nanoestruturas/química , Nanoestruturas/efeitos da radiação , Polímeros/química , Polímeros/efeitos da radiação , Porosidade/efeitos da radiação , Simulação por Computador , Campos Eletromagnéticos , Nanoestruturas/ultraestruturaRESUMO
We show that diffusion currents for a membrane containing a single conical nanopore with a fixed surface charge and small enough opening diameter depend on the concentration gradient direction. We interpret the results based on the effect of salt concentration on the thickness of the electrical double layer within the nanopore associated with the nanopore's surface charge and the distribution of electric fields inside the pore. The experimental observations are described by a diffusional model based on the Smoluchowski-Nernst-Planck equation.
Assuntos
Cloro/química , Potenciais da Membrana , Membranas Artificiais , Modelos Químicos , Nanoestruturas/química , Polietilenotereftalatos/química , Potássio/química , Simulação por Computador , Difusão , Permeabilidade , PorosidadeRESUMO
We present a synthetic nanodevice, which transports potassium ions against their concentration gradient if stimulated with external field fluctuations. It consists of a single, conical pore, created in a thin polyethylene terephthalate film. The pumping mechanism is similar to one of longitudinally oscillating deterministic ratchets.
RESUMO
The transport characteristics of nanofabricated synthetic pores of similar dimensions to those of biological channels is reported. By comparison of the ion current through single synthetic and biological channels we show that the 1/f(alpha) noise indeed originates from the channel's opening-closing process. Strong evidence has been provided that the latter is related to the underlying motions of channel wall constituents.
Assuntos
Canais Iônicos/química , Canais de Potássio/química , Animais , Gafanhotos , Membranas Artificiais , Nanotecnologia/métodos , Canais de Potássio/fisiologia , Análise EspectralRESUMO
The statistical analysis of an ionic current signal recorded from a single channel of a biological membrane is presented. We find the main characteristics of the ionic current probability density, the closed- and open-state distributions, and the autocorrelation function of the current recordings by using procedures based on the kernel and tail estimators, the bootstrap methodology; and the Zipf plots. The results provide evidence for the non-Markovian character of the channel kinetics of the investigated data.
