Current-Induced Magnetic Skyrmions with Controllable Polarities in the Helical Phase

We report the current-induced creation of magnetic skyrmions in a chiral magnet FeGe nanostructure by using in situ Lorentz transmission electron microscopy. We show that magnetic skyrmions with controllable polarity can be transferred from the helical ground state simply by controlling the direction of the current flow at zero magnetic fields. The force analysis and symmetry consideration, backed up by micromagnetic simulations, well explain the experimental results, where magnetic skyrmions are created because of the edge instability of the helical state in the presence of spin-transfer torque. The on-demand generation of skyrmions and control of their polarity by electric current without the need for a magnetic field will enable novel purely electric-controlled skyrmion devices.

Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in the form of miniaturized instrument. Analytes may exist in the form of positively or negatively charged ions according to their chemical composition and ionization condition, and therefore require both polarity of electric field for the detection. In this work the polarity switching of a drift-time ion mobility spectrometer based on a direct current (DC) corona discharge ionization source was investigated, with novel solutions for both the control of ion shutter and the stabilization of aperture grid. The drift field is established by employing a switchable high voltage power supply and a serial of voltage regulator diode, with optocouplers to drive the ion shutter when the polarity is switched. The potential of aperture grid is stabilized during the polarity switching by the use of four diodes to avoid unnecessary charging cycle of the aperture grid capacitor. Based on the proposed techniques, the developed DT-IMS with 50 mm drift path is able to switch its polarity in 10 ms and acquire mobility spectrum after 10 ms of stabilization. Coupled with a thermal desorption sampler, limit of detection (LoD) of 0.1 ng was achieved for ketamine and TNT. Extra benefits include single calibration substance for both polarities and largely simplified pneumatic design, together with the reduction of second drift tube and its accessories. This work paved the way towards further miniaturization of DT-IMS without compromise of performance.

Lateral Fully Organic P-N Diodes Created in a Single Donor-Acceptor Copolymer

P-N junctions exist in many solid-state organic devices, such as light-emitting diodes, solar cells, and thermoelectric devices. Creating P-N junctions by bulk chemical doping in a single organic material (like silicon doped by boron and phosphorus) may capitalize the vast scientific and technological groundwork established in the inorganic semiconducting field. However, high-performance single-organic-material P-N junctions are seldom reported, because the diffusion of the dopant counterions often leads to transient rectification properties. Herein, a new type of lateral fully organic diodes created in single donor-acceptor (D-A) copolymer films with only one P-type dopant is reported. The achieved lateral devices exhibit high current densities of ≈3.83 A cm^-2 and a high rectification ratio of ≈2100, which are beyond the requirements for high-frequency identification tags. The P- to N-type polarity switching mechanism is proposed after spectroscopic and structural tests. Decent stability of the organic diode is obtained, which is due to the long channel length and low diffusion speed of the large size of dopants. This work opens the opportunities to create P-N junctions in ways of silicon-based inorganic semiconductors and promises new opportunities for integrating organic materials for flexible and printable organic devices.

In Situ Deprotection of Polymeric Binders for Solution-Processible Sulfide-Based All-Solid-State Batteries

Sulfide-based all-solid-state batteries (ASSBs) have been featured as promising alternatives to the current lithium-ion batteries (LIBs) mainly owing to their superior safety. Nevertheless, a solution-based scalable manufacturing scheme has not yet been established because of the incompatible polarity of the binder, solvent, and sulfide electrolyte during slurry preparation. This dilemma is overcome by subjecting the acrylate (co)polymeric binders to protection-deprotection chemistry. Protection by the tert-butyl group allows for homogeneous dispersion of the binder in the slurry based on a relatively less polar solvent, with subsequent heat-treatment during the drying process to cleave the tert-butyl group. This exposes the polar carboxylic acid groups, which are then able to engage in hydrogen bonding with the active cathode material, high-nickel layered oxide. Deprotection strengthens the electrode adhesion such that the strength equals that of commercial LIB electrodes, and the key electrochemical performance parameters are improved markedly in both half-cell and full-cell settings. The present study highlights the potential of sulfide-based ASSBs for scalable manufacturing and also provides insights that protection-deprotection chemistry can generally be used for various battery cells that suffer from polarity incompatibility among multiple electrode components.

IsoSearch: An Untargeted and Unbiased Metabolite and Lipid Isotopomer Tracing Strategy from HR-LC-MS/MS Datasets

Stable isotopic tracer analysis is a technique used to determine carbon or nitrogen atom incorporation into biological systems. A number of mass spectrometry based approaches have been developed for this purpose, including high-resolution tandem mass spectrometry (HR-LC-MS/MS), selected reaction monitoring (SRM) and parallel reaction monitoring (PRM). We have developed an approach for analyzing untargeted metabolomic and lipidomic datasets using high-resolution mass spectrometry with polarity switching and implemented our approach in the open-source R script IsoSearch and in Scaffold Elements software. Using our strategy, which requires an unlabeled reference dataset and isotope labeled datasets across various biological conditions, we traced metabolic isotopomer alterations in breast cancer cells (MCF-7) treated with the metabolic drugs 2-deoxy-glucose, 6-aminonicotinamide, compound 968, and rapamycin. Metabolites and lipids were first identified by the commercial software Scaffold Elements and LipidSearch, then IsoSearch successfully profiled the ¹³C-isotopomers extracted metabolites and lipids from ¹³C-glucose labeled MCF-7 cells. The results interpreted known models, such as glycolysis and pentose phosphate pathway inhibition, but also helped to discover new metabolic/lipid flux patterns, including a reactive oxygen species (ROS) defense mechanism induced by 6AN and triglyceride accumulation in rapamycin treated cells. The results suggest the IsoSearch/Scaffold Elements platform is effective for studying metabolic tracer analysis in diseases, drug metabolism, and metabolic engineering for both polar metabolites and non-polar lipids.

Tuning the Polarity of MoTe2 FETs by Varying the Channel Thickness for Gas-Sensing Applications

In this study, electrical characteristics of MoTe2 field-effect transistors (FETs) are investigated as a function of channel thickness. The conductivity type in FETs, fabricated from exfoliated MoTe2 crystals, switched from p-type to ambipolar to n-type conduction with increasing MoTe2 channel thickness from 10.6 nm to 56.7 nm. This change in flake-thickness-dependent conducting behavior of MoTe2 FETs can be attributed to modulation of the Schottky barrier height and related bandgap alignment. Change in polarity as a function of channel thickness variation is also used for ammonia (NH3) sensing, which confirms the p- and n-type behavior of MoTe2 devices.

Analysis of Six β-Lactam Residues in Milk and Egg by Micellar Electrokinetic Chromatography with Large-Volume Sample Stacking and Polarity Switching

A new micellar electrokinetic chromatography method with large-volume sample stacking and polarity switching was developed to analyze amoxicllin, cephalexin, oxacillin, penicillin G, cefazolin, and cefoperazone in milk and egg. The important parameters influencing separation and enrichment factors were optimized. The optimized running buffer consisted of 10 mM phosphate and 22 mM SDS at pH 6.7. The sample size was 1.47 kPa × 690 s, the reverse voltage was 20 kV, and the electric current recovery was 95%. Under these optimum conditions, the enrichment factors of six β-lactams were 193-601. Their LODs were <0.26 ng/g, and LOQs were all 2 ng/g, which was only 1/50-1/2 of the maximum residual limits demanded by U.S. and Japanese regulations. The intraday and interday RSDs of method were lower than 3.70 and 3.91%, respectively. The method can be applied to determine these six antibiotic residues in egg and milk.

The 4-pyridylmethyl ester as a protecting group for glutamic and aspartic acids: 'flipping' peptide charge states for characterization by positive ion mode ESI-MS

Use of the 4-pyridylmethyl ester group for side-chain protection of glutamic acid residues in solid-phase peptide synthesis enables switching of the charge state of a peptide from negative to positive, thus making detection by positive ion mode ESI-MS possible. The pyridylmethyl ester moiety is readily removed from peptides in high yield by hydrogenation. Combining the 4-pyridylmethyl ester protecting group with benzyl ester protection reduces the number of the former needed to produce a net positive charge and allows for purification by RP HPLC. This protecting group is useful in the synthesis of highly acidic peptide sequences, which are often beset by problems with purification by standard RP HPLC and characterization by ESI-MS.

A comparison of five lipid extraction solvent systems for lipidomic studies of human LDL

Lipidome profile of fluids and tissues is a growing field as the role of lipids as signaling molecules is increasingly understood, relying on an effective and representative extraction of the lipids present. A number of solvent systems suitable for lipid extraction are commonly in use, though no comprehensive investigation of their effectiveness across multiple lipid classes has been carried out. To address this, human LDL from normolipidemic volunteers was used to evaluate five different solvent extraction protocols [Folch, Bligh and Dyer, acidified Bligh and Dyer, methanol (MeOH)-tert-butyl methyl ether (TBME), and hexane-isopropanol] and the extracted lipids were analyzed by LC-MS in a high-resolution instrument equipped with polarity switching. Overall, more than 350 different lipid species from 19 lipid subclasses were identified. Solvent composition had a small effect on the extraction of predominant lipid classes (triacylglycerides, cholesterol esters, and phosphatidylcholines). In contrast, extraction of less abundant lipids (phosphatidylinositols, lyso-lipids, ceramides, and cholesterol sulfates) was greatly influenced by the solvent system used. Overall, the Folch method was most effective for the extraction of a broad range of lipid classes in LDL, although the hexane-isopropanol method was best for apolar lipids and the MeOH-TBME method was suitable for lactosyl ceramides.