This Communication demonstrates a method that generates parallel fibers via electrospinning (ES) magnetic-particledoped polymers in a magnetic field. ES is a simple method for generating ultrathin fibers with diameters ranging from tens of nanometers to tens of micrometers. [1][2][3][4][5] ES possesses several attractive features: comparatively low-cost, relatively high production rate, the ability to generate materials with large surface area-to-volume ratios, and applicability to many types of materials. These features have enabled many applications. [6][7][8][9][10] During electrospinning, the fibers deposited on the collector are typically randomly oriented in the form of nonwoven mats. It is desirable to generate periodic structures to broaden the applications of ES. For example, in the fabrication of electronic and photonic devices, well-aligned and highly ordered architectures are often required. [11,12] For application of fiber-reinforced polymer composites, the alignment of fibers can improve mechanical properties. [13] Well-ordered fibers may also be suitable for many applications in tissue engineering. [8,14] There have been a few approaches to improving the orderliness of electrospun fibers. [15][16][17][18][19][20][21][22][23][24][25][26][27] Matthews et al. [25] used a rotating mandrel as a ground target to collect fibers. By controlling the rotation speed of the mandrel, they obtained collagen fibers aligned along the axis of rotation. Katta et al. [16] employed a macroscopic copper wireframed rotating drum as the collector, and the electrospun fibers collected on the drum as it rotated were parallel to each other. Theron et al. [26] described an electrostatic field-assisted assembly technique using a tapered and grounded wheel-like bobbin to position and align individual nanofibers into parallel arrays. Because the edge of the bobbin was relatively sharp, this technique could not fabricate well-aligned nanofibers over large areas. Li et al. [15,17] fabricated parallel arrays made of polymeric and ceramic nanofibers using a collector consisting of two pieces of electrically conductive substrate separated by a gap. To sum up, existing strategies for making parallel electrospun fibers include modifying the collectors and manipulating the electrical field. These methods can fabricate more or less aligned fibers; however, they still have some drawbacks. Modifying the collectors, such as rotating drums, is a time-and energy-consuming method; moreover fibers fabricated by this method are poorly aligned and cannot be conveniently transferred to different types of substrates. Methods based on electrical fields do not seem to achieve the fabrication of aligned fibers over large areas. It is therefore necessary to explore new and more reliable methods that generate wellaligned electrospun polymeric fibers over large areas. Herein, we report a facile and effective approach to fabricating well-aligned arrays and multilayer grids by a technique called magnetic electrospinning (MES; Scheme 1), where magnetized f...

The first electronic measurement of DNA translocation through ultrathin BN nanopores is demonstrated. BN nanopores show much higher detection sensitivity compared with SiN nanopores. BN has a spatial resolution as graphene. The ultrathin BN nanopores provide substantial opportunities in realizing high-spatial-sensitivity nanopore electrical devices for various applications.

We describe experiments and modeling results that reveal and explain the distribution of times that identical double-stranded DNA (dsDNA) molecules take to pass through a voltage-biased solid-state nanopore. We show that the observed spread in this distribution is caused by viscous-drag-induced velocity fluctuations that are correlated with the initial conformation of nanopore-captured molecules. This contribution exceeds that due to diffusional Brownian motion during the passage. Nevertheless, and somewhat counterintuitively, the diffusional Brownian motion determines the fundamental limitations of rapid DNA strand sequencing with a nanopore. We model both diffusional and conformational fluctuations in a Langevin description. It accounts well for passage time variations for DNA molecules of different lengths, and predicts conditions required for low-error-rate nanopore-strand DNA sequencing with nanopores.

Voltage-biased solid-state nanopores are well established in their ability to detect and characterize single polymers, such as DNA, in electrolytes. The addition of a pressure gradient across the nanopore yields a second molecular driving force that provides new freedom for studying molecules in nanopores. In this work, we show that opposing pressure and voltage bias enables nanopores to detect and resolve very short DNA molecules, as well as to detect near-neutral polymers.

Nanopores in graphene membranes can potentially offer unprecedented spatial resolution for single molecule sensing, but their fabrication has thus far been difficult, poorly scalable, and prone to contamination. We demonstrate an fabrication method that nucleates and controllably enlarges nanopores in electrolyte solution by applying ultra-short, high-voltage pulses across the graphene membrane. This method can be used to rapidly produce graphene nanopores with subnanometer size accuracy in an apparatus free of nanoscale beams or tips.

A detailed understanding of the origin of the electrophoretic force on DNA molecules in a solid-state nanopore is important for the development of nanopore-based sequencing technologies. Because of the discrepancies between recent attempts to predict this force and both direct and indirect experimental measurements, this topic has been the focus of much recent discussion. We show that the force is predictable to very good accuracy if all of the experimental conditions are accounted for properly. To resolve this issue, we compare the calculation efficiency and accuracy of numerical solutions of Poisson-Boltzmann and Poisson-Nernst-Planck descriptions of electrolyte behavior in the nanopore in the presence of DNA molecules. Two geometries--axially symmetric and cross-sectional--are compared and shown to be compatible. Numerical solutions are carried out on a sufficiently fine mesh to evaluate the viscous drag force acting on DNA inside a silicon nitride nanopore. By assuming the DNA is immobilized in the axial center of the nanopore, the calculation result of this viscous drag force is found to be rather larger than the experimental result. Because the viscous drag force decreases if DNA is closer to the surface of the nanopore, however, the relevant effective driving force is the average over all possible positions of the DNA in the nanopore. When this positional uncertainty is taken into account, the effective driving force acting on DNA inside the nanopore is found to agree very well with the experimental results.

We report the formation of a tunable single DNA molecule trap near a solid-state nanopore in an electrolyte solution under conditions where an electric force and a pressure-induced viscous flow force on the molecule are nearly balanced. Trapped molecules can enter the pore multiple times before escaping the trap by passing through the pore or by diffusing away. Statistical analysis of many individually trapped molecules yields a detailed picture of the fluctuation phenomena involved, which are successfully modeled by a one-dimensional first passage approach.

Extensive applications for photodetectors have led to demand for high‐responsivity polarization‐sensitive light detection. Inspired by the elaborate architecture of butterfly Papilio paris, a 1D nanograting bonded porous 2D photonic crystal perovskite photodetector (G‐PC‐PD) using a commercial DVD master and 2D crystalline colloidal arrays template was fabricated. The coupling effect from grating diffraction and reflection of the PC stopband renders the enhanced light harvesting of G‐PC‐PD. The porous scaffold and nanoimprinting process afford a highly crystalline perovskite film. White light responsivity and detectivity of G‐PC‐PD are up to 12.67 A W−1 and 3.22×1013 Jones (6∼7 times that of a pristine perovskite photodetector). The highly ordered nanograting arrays of G‐PC‐PD enable polarization‐sensitive light detection with a rate of −0.72 nA deg−1. This hierarchical perovskite integrated nanograting and 2D PC architecture opens a new avenue to high‐performance optoelectronic devices.