The Principle of Calibration Using the Ionic Current——A New Calibration Method for Electro-Magnetic Flowmeters

An equivalent relationship between electro magnetic flowmeters (EMFs) and the Hall effect is discussed in principle and three equivalent conclusions about their measuring equations are derived. Thereby,the calibration using the ionic current (CUIC) is introduced to the calibration of EMFs in a special Hall effect system. A basic system with these equations is specially given and discussed for realizing the method. Two key points about CUIC are proved by a simple experiment.

Determination of Atomic Fractions of Isotopes Carbon-13 and Nitrogen-15 Directly in Glicine, L-Leucine, Isoleucine and Alanine

Using compounds modified by the isotopes carbon-13 and nitrogen-15 helps conduct research in various fields of science, such as medicine, pharmacology, pharmacokinetics, metabolism, agriculture, and others. In the case of the availability of reliable, express, and cheap methods, the area of their use will gradually expand. A determination of the atomic fraction of the isotopes carbon-13 and nitrogen-15 directly in glycine, leucine, isoleucine, and alanine is proposed;the modification concerns all centers or one or more identical carbon and nitrogen centers separately, as well as both isotopes at the same time. There are defined mass lines of the mass spectrum of each amino acid, through which the isotopic content of carbon and nitrogen is calculated. The processes that must be taken into account for the determination of the isotopic content are also established. Isotopic analysis of these compounds until now was carried out by transforming them into carbon oxide, dioxide, and molecular nitrogen, and determination of their content in individual centers was impossible.

Ion and water transport in charge-modified graphene nanopores

Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the coion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl-ion current increases and reaches a plateau, and the Na＋current decreases as the charge amount increases in systems in which Na＋ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges.

Ionic current rectification in asymmetric nanofluidic devices

In recent decades,the properties and behaviors of nanofluidic devices have been widely explored in varied subjects such as engineering,physics,chemistry,and biology.Among the rich properties of nanofluidics,ionic current rectification(ICR) is a unique phenomenon arising from asymmetric nanofluidic devices with electric double layer(EDL) overlapped.The ICR property is especially useful in applications including energy conversion,mass separation,sea water purification and bioanalysis.In this review,the ICR property in nanofluidics as well as the underlying mechanism is demonstrated.The influencing factors concerning to the ICR property are systematically summarized.The asymmetric geometry as well as the charge distribution is in charge of the ICR behavior occurring in nanofluidic devices.This review is aimed at readers who are interested in the fundamentals of mass transport in nanofluidics in general,as well as those who are willing to apply nanofluidics in various research fields.

Fabrication of Biomimetic Transparent and Flexible Pectin/PEG Composite Film for Temperature Sensing Applications

In the field of robotics to enhance the interaction with humans in real-time and in the bioengineering field to develop prosthetic devices, the need for artificial skin is in high demand. In this work, the hydrogen-bonded complex network structure of the Pectin/PEG composite has been designed, resulting in the free-standing film functioning as a temperature-sensing device. With the gelation technique and the addition of PEG, the film’s flexibility and conductivity were enhanced. The fabricated device worked at a low voltage of 1 V supply with high throughput. With different dimensions, three devices were fabricated, and the maximum-induced ionic current was 34 µA ± 5%. The device has an average sensitivity of 1.3–2.7 µA/°C over the range of 30 °C to 42 °C. The device's fastest response time to sense the temperature change was 2 s ± 5%. The present device exhibits good stability for a long duration of time. These pectin/PEG films can be used as biomimetic skin to improve the efficiency in sensing the temperature.

Molecular dynamics simulation on DNA translocating through MoS_(2) nanopores with various structures

The emergence of MoS_(2) nanopores has provided a new avenue for high performance DNA sequencing,which is critical for modem chemical/biological research and applications.Herein,molecular dynamics simulations were performed to design a conceptual device to sequence DNA with MoS_(2) nanopores of different structures(e.g.,pore rim contained Mo atoms only,S atoms only,or both Mo and S atoms),where various unfolded single-stranded DNAs(ssDNAs)translocated through the nanopores driven by transmembrane bias;the sequence content was identified by the associating ionic current.All ssDNAs adsorbed onto the MoS_(2) surface and translocated through the nanopores by transmembrane electric field in a stepwise manner,where the pause between two permeation events was long enough for the DNA fragments in the nanopore to produce well-defined ionic blockage current to deduce the DNA’s base sequence.The transmembrane bias and DNA-MoS_(2) interaction could regulate the speed of the translocation process.Furthermore,the structure(atom constitution of the nanopore rim)of the nanopore considerably regulated both the translocate process and the ionic current.Thus,MoS_(2) nanopores could be employed to sequence DNA with the flexibility to regulate the translocation process and ionic current to yield the optimal sequencing performance.

A Stabilized Finite Element Method for Modified Poisson-Nernst-Planck Equations to Determine Ion Flow Through a Nanopore

The conventional Poisson-Nernst-Planck equations do not account for the finite size of ions explicitly.This leads to solutions featuring unrealistically high ionic concentrations in the regions subject to external potentials,in particular,near highly charged surfaces.A modified form of the Poisson-Nernst-Planck equations accounts for steric effects and results in solutions with finite ion concentrations.Here,we evaluate numerical methods for solving the modified Poisson-Nernst-Planck equations by modeling electric field-driven transport of ions through a nanopore.We describe a novel,robust finite element solver that combines the applications of the Newton’s method to the nonlinear Galerkin form of the equations,augmented with stabilization terms to appropriately handle the drift-diffusion processes.To make direct comparison with particle-based simulations possible,our method is specifically designed to produce solutions under periodic boundary conditions and to conserve the number of ions in the solution domain.We test our finite element solver on a set of challenging numerical experiments that include calculations of the ion distribution in a volume confined between two charged plates,calculations of the ionic current though a nanopore subject to an external electric field,and modeling the effect of a DNA molecule on the ion concentration and nanopore current.