Single-molecule detection and characterization with nanopores is a powerful technique that does not require labeling. Multinanopore systems, especially double nanopores, have attracted wide attention and have been applied in many fields. However, theoretical studies of electrokinetic ion transport in nanopores mainly focus on single nanopores. In this paper, for the first time, a theoretical study of pH-regulated double-barreled nanopores is conducted using three-dimensional Poisson–Nernst–Planck equations and Navier–Stokes equations. Four ionic species and the surface chemistry on the walls of the nanopores are included. The results demonstrate that the properties of the bulk salt solution significantly affect nanopore conductivity and ion transport phenomena in nanopores. There are two ion-enriched zones and two ion-depleted zones in double-barreled nanopores. Due to the symmetry of the double-barreled nanopore structure and surface charge density, there is no ionic rectification effect in double-barreled nanopores. The ion selectivity is similar to that of conventional single pH-regulated nanopores.
The traditional quantitative analysis methods of ascorbic acid (AA), which require expensive equipment, a large amount of samples and professional technicians, are usually complex and time-consuming. A low-cost and high-efficiency AA detection device is reported in this work. It integrates a three-electrode sensor module prepared by screen printing technology, and a microfluidic chip with a finger-actuated micropump peeled from the liquid-crystal display (LCD) 3D printing resin molds. The AA detection process on this device is easy to operate. On-chip detection has been demonstrated to be 2.48 times more sensitive than off-chip detection and requires only a microliter-scale sample volume, which is much smaller than that required in traditional electrochemical methods. Experiments show that the sample and buffer can be fully mixed in the microchannel, which is consistent with the numerical simulation results wherein the mixing efficiency is greater than 90%. Commercially available tablets and beverages are also tested, and the result shows the reliability and accuracy of the device, demonstrating its broad application prospects in the field of point-of-care testing (POCT).
Vitamins are essential and necessary nutrients for the human body. Rapid and accurate quantification of their levels in various samples has attracted much attention. Compared with traditional analytical methods, electrochemical techniques, with the advantages of low cost, high sensitivity, flexible detection strategies, easy integration, and miniaturization, have gradually become the main tools in vitamin detection. In this paper, the advance of electrochemical sensing of vitamins in recent years is reviewed. Firstly, the basics of different vitamins are briefly introduced. Then, the commonly-used electrodes and electrochemical methods for vitamin electrochemical detection, as well as the specific implementation strategy and performance, are described in detail. The development of miniaturization devices, especially microfluidic and microsensor devices, is also presented. Finally, the challenges faced by the electrochemical detection of vitamins are discussed, and future development is prospected.
Cell electroporation is an important cell manipulation technology to artificially transfer specific extracellular components into cells. However, the consistency of substance transport during the electroporation process is still an issue due to the wide size distribution of the natural cells. In this study, a cell electroporation microfluidic chip based on a microtrap array is proposed. The microtrap structure was optimized for single-cell capture and electric field focusing. The effects of the cell size on the cell electroporation in the microchip were investigated through simulation and experiment methods using the giant unilamellar vesicle as the simplified cell model, and a numerical model of a uniform electric field was used as a comparison. Compared with the uniform electric field, a lower threshold electric field is required to induce electroporation and produces a higher transmembrane voltage on the cell under a specific electric field in the microchip, showing an improvement in cell viability and electroporation efficiency. The larger perforated area produced on the cells in the microchip under a specific electric field allows a higher substance transfer efficiency, and the electroporation results are less affected by the cell size, which is beneficial for improving substance transfer consistency. Furthermore, the relative perforation area increases with the decrease of the cell diameter in the microchip, which is exactly opposite to that in a uniform electric field. By manipulating the electric field applied to the microtrap individually, a consistent proportion of substance transfer during electroporation of cells with different sizes can be achieved.
Nanopore single-molecule technology, especially DNA/RNA sequencing based on nanopores, requires a high spatial resolution. In this paper, we theoretically studied the spatial resolution of the cross-disjoint mortise-confined solid-state nanopore (CDM-nanopore) structure that is formed by two perpendicular and disjoint nanochannels and a middle nanopore. When the thickness of the middle layer (nanopore) is 0 nm (i.e., the zero-depth interfacial nanopore), 0.6 nm, and 1 nm, the geometric resolution (δ z ) is 0.24, 0.32, and 0.39 nm, respectively. The ultrahigh spatial resolution of the CDM nanopore with an ultrathin middle layer is comparable with that of the conventional ultrashort nanopore (e.g., two-dimensional material nanopore). We also demonstrate that for cylindrical segments with a diameter difference of 0.2 nm, the current difference (δ I ) will reach the maximum when the middle layer is about half of the length of one segment. In addition to the high resolution of CDM nanopores with an ultrathin middle layer, its outstanding mechanical stability and low noise characteristics provide the possibility of extending the application of the CDM nanopore to DNA/RNA sequencing.
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