Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userModulation of Ionic Current Rectification in Ultra-Short Conical Nanopores
83
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Nanopores that exhibit ionic current rectification (ICR) behave like diodes, such that they transport ions more efficiently in one direction than the other. Conical nanopores have been shown to rectify ionic current, but only those with at least 500 nm in length exhibit significant ICR. Here, through the finite element method, we show how ICR of conical nanopores with length below 200 nm can be tuned by controlling individual charged surfaces i.e. inner pore surface (surface_inner), and exterior pore surfaces on the tip and base side (surface_tip and surface_base). The charged surface_inner and surface_tip can induce obvious ICR individually, while the effects of the charged surface_base on ICR can be ignored. The fully charged surface_inner alone could render the nanopore counterion-selective and induces significant ion concentration polarization in the tip region, which causes reverse ICR compared to nanopores with all surface charged. In addition, the direction and degree of rectification can be further tuned by the depth of the charged surface_inner. When considering the exterior membrane surface only, the charged surface_tip causes intra-pore ionic enrichment and depletion under opposite biases which results in significant ICR. Its effective region is within ~40 nm beyond the tip orifice. We also found that individual charged parts of the pore system contributed to ICR in an additive way due to the additive effect on the ion concentration regulation along the pore axis. With various combinations of fully/partially charged surface_inner and surface_tip, diverse ICR ratios from ~2 to ~170 can be achieved. Our findings shed light on the mechanism of ionic current rectification in ultra-short conical nanopores, and provide a useful guide to the design and modification of ultra-short conical nanopores in ionic circuits and nanofluidic sensors.
rate research
Read More
Nanopores in solid state membranes are a tool able to probe nanofluidic phenomena or can act as a single molecular sensor. They also have diverse applications in filtration, desalination or osmotic power generation. Many of these applications involve chemical, or hydrostatic pressure differences, which act on both the supporting membrane and the ion transport through the pore. By using pressure differences between the sides of the membrane, and an alternating current approach to probe ion transport, we investigate two distinct physical phenomena: the elastic deformation of the membrane through the measurment of strain at the nanopore, and the growth of ionic current rectification with pressure due to pore entrance effects.
Ion transport in biological and synthetic nanochannels is characterized by phenomena such as ion current fluctuations and rectification. Recently, it has been demonstrated that nanofabricated synthetic pores can mimic transport properties of biological ion channels [P. Yu. Apel, {it et al.}, Nucl. Instr. Meth. B {bf 184}, 337 (2001); Z. Siwy, {it et al.}, Europhys. Lett. {bf 60}, 349 (2002)]. Here, the ion current rectification is studied within a reduced 1D Poisson-Nernst-Planck (PNP) model of synthetic nanopores. A conical channel of a few $mathrm{nm}$ to a few hundred of nm in diameter, and of few $mu$m long is considered in the limit where the channel length considerably exceeds the Debye screening length. The rigid channel wall is assumed to be weakly charged. A one-dimensional reduction of the three-dimensional problem in terms of corresponding entropic effects is put forward. The ion transport is described by the non-equilibrium steady-state solution of the 1D Poisson-Nernst-Planck system within a singular perturbation treatment. An analytic formula for the approximate rectification current in the lowest order perturbation theory is derived. A detailed comparison between numerical results and the singular perturbation theory is presented. The crucial importance of the asymmetry in the potential jumps at the pore ends on the rectification effect is demonstrated. This so constructed 1D theory is shown to describe well the experimental data in the regime of small-to-moderate electric currents.
Solid-state nanopores are promising tools for single molecule detection of both DNA and proteins. In this study, we investigate the patterns of ionic current blockades as DNA translocates into or out of the geometric confinement of such conically shaped pores. We studied how the geometry of a nanopore affects the detected ionic current signal of a translocating DNA molecule over a wide range of salt concentration. The blockade level in the ionic current depends on the translocation direction at a high salt concentration, and at lower salt concentrations we find a non-intuitive ionic current decrease and increase within each single event for the DNA translocations exiting from confinement. We use recently developed DNA rulers with markers and finite element calculations to explain our observations. Our calculations explain the shapes of the signals observed at all salt concentrations and show that the unexpected current decrease and increase are due to the competing effects of ion concentration polarization and geometric exclusion of ions. Our analysis shows that over a wide range of geometry, voltage and salt concentrations we are able to understand the ionic current signals of DNA in asymmetric nanopores enabling signal optimization in molecular sensing applications.
Gate-induced modulation of the spin-orbit interaction (SOI) in a 1.5 nm-thick Pd thin film grown on a ferrimagnetic insulator was investigated. Efficient charge accumulation by ionic gating enables a substantial upshift in the Fermi level of the Pd film, which was corroborated by suppression of the resistivity in the Pd. Electromotive forces arising from the inverse spin Hall effect in Pd under spin pumping were substantially modulated by the gating, in consequence of the modulation of the spin Hall conductivity of Pd as in an ultrathin Pt film. The same experiment using a thin Cu film, for which the band structure is largely different from Pd and Pt and its SOI is quite small, provides further results supporting our claim. The results obtained help in developing a holistic understanding of the gate-tunable SOI in solids and confirm a previous explanation of the significant modulation of the spin Hall conductivity in an ultrathin Pt film by gating.
Applications relying on mid-infrared radiation (Mid-IR, $lambdasim$ 3-30 $mu$m) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs. Mid-IR cameras have propelled the field of thermal imaging. And the invention of the quantum cascade laser (QCL) has been a milestone, making compact, semiconductor-based mid-IR lasers available to a vast range of applications. All the recent breakthrough advances stemmed from the development of a transformative technology. In addition to the generation and detection of light, a key functionality for most photonics systems is the electrical control of the amplitude and/or phase of an optical beam at ultra-fast rates (GHz or more). However, standalone, broadband, integrated modulators are missing from the toolbox of present mid-IR photonics integrated circuits and systems developers. We have developed a free-space amplitude modulator for mid-IR radiation ($lambdasim$ 10 $mu$m) that can operate up to at least 1.5 GHz (-3dB cut-off at $sim$ 750 MHz) and at room-temperature. The device relies on a semiconductor hetero-structure enclosed in a judiciously designed metal-metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime. The large change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR continuous-wave laser up to speeds of more than 1.5 GHz.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
