Surface oxidation of commercial activated carbon with enriching carboxyl groups for high-yield electrocatalytic H2O2production.

Two-electron oxygen reduction reaction (2e-ORR) for H2O2production is regarded as a more ecologically friendly substitute to the anthraquinone method. However, the search of selective and cheap catalysts is still challenging. Herein, we developed a neutral-selective and efficient nonprecious electrocatalyst that was prepared from a commercial activated carbon (AC) by simply microwave-assisted ash impurity elimination and hydrogen peroxide oxidation for surface functional sites optimization. The oxygen configuration can be tuned with enriching carboxyl group up to 6.65 at.% by the dosage of hydrogen peroxide (mass ratio of H2O2/C = ∼0-8.3). Chemical titration experiments identified the carbonyl groups as the most potential active sites, with selectivity boosted by the additional carboxyl groups. The microwave-assisted moderate-oxidized activated carbon (MW-AC5.0) demonstrated optimal 2e-ORR activity and selectivity in neutral electrolyte (0.1 M K2SO4), with H2O2selectivity reaching ∼75%-97%, a maximum H2O2production rate (1.90 mol·gcatal-1·h-1@0.1 V) and satisfying faradaic efficiency (∼85%) in gas-diffusion-electrode. When coupled with Fenton reaction, it can degrade a model organic pollutant (methylene blue [MB], 50 ppm) to colorless in a short time of 20 min, indicating the potential applications in the environmental remediation.

Nitrogen-doped hollow mesoporous carbon spheres for efficient oxygen reduction.

Extensive investigations have been devoted to nitrogen-doped carbon materials as catalysts for the oxygen reduction reaction (ORR) in various conversion technologies. In this study, we introduce nitrogen-doped carbon materials with hollow spherical structures. These materials demonstrate significant potential in ORR activity within alkaline media, showing a half-wave potential of 0.87 V versus the reversible hydrogen electrode (RHE). Nitrogen-doped hollow carbon spheres (N-CHS) exhibit unique characteristics such as a thin carbon shell layer, hollow structure, large surface area, and distinct pore features. These features collectively create an optimal environment for facilitating the diffusion of reactants, thereby enhancing the exposure of active sites and improving catalytic performance. Building upon the promising qualities of N-CHS as a catalyst support, we employ heme chloride (1 wt%) as the source of iron for Fe doping. Through the carbonization process, Fe-N active sites are effectively formed, displaying a half-wave potential of 0.9 V versus RHE. Notably, when implemented as a cathode catalyst in zinc-air batteries, this catalyst exhibits an impressive power density of 162.6 mW cm-2.

Fluorescence turn-on detection of human serum albumin based on the assembly of gold nanoclusters and bromocresol green.

As the most abundant protein in plasma, human serum albumin plays a vital role in physiological processes, such as maintaining blood osmotic pressure and carrying small-molecule ligands. Since the content of albumin in the human serum can reflect the status of liver and renal function, albumin quantitation is significant in clinical diagnosis. In this work, fluorescence turn-on detection of human serum albumin (HSA) had been performed based on the assembly of gold nanoclusters and bromocresol green. Gold nanoclusters (AuNCs) capped by reduced glutathione (GSH) were assembled with bromocresol green (BCG), and the assembly was used as a fluorescent probe for HSA. After BCG assembling, the fluorescence of gold nanoclusters was nearly quenched. In acidic solution, HSA can selectively bind to BCG on the assembly and recover the fluorescence of the solution. Based on this turn-on fluorescence, ratiometric HSA quantification was realized. Under optimal conditions, HSA detection by the probe possessed a good linear relationship in the range of 0.40-22.50 mg·mL-1, and the detection limit was 0.27 ± 0.04 mg·mL-1 (3σ, n = 3). Common coexisting components in serum and blood proteins did not interfere with the detection of HSA. This method has the advantages of easy manipulation and high sensitivity, and the fluorescent response is insensitive to reaction time.

Non-Enzymatically Colorimetric Bilirubin Sensing Based on the Catalytic Structure Disruption of Gold Nanocages.

As an essential indicator of liver function, bilirubin is of great significance for clinical diagnosis. A non-enzymatic sensor has been established for sensitive bilirubin detection based on the bilirubin oxidation catalyzed by unlabeled gold nanocages (GNCs). GNCs with dual-localized surface plasmon resonance (LSPR) peaks were prepared by a one-pot method. One peak around 500 nm was ascribed to gold nanoparticles (AuNPs), and the other located in the near-infrared region was the typical peak of GNCs. The catalytic oxidation of bilirubin by GNCs was accompanied by the disruption of cage structure, releasing free AuNPs from the nanocage. This transformation changed the dual peak intensities in opposite trend, and made it possible to realize the colorimetric sensing of bilirubin in a ratiometric mode. The absorbance ratios showed good linearity to bilirubin concentrations in the range of 0.20~3.60 µmol/L with a detection limit of 39.35 nM (3σ, n = 3). The sensor exhibited excellent selectivity for bilirubin over other coexisting substances. Bilirubin in real human serum samples was detected with recoveries ranging from 94.5 to 102.6%. The method for bilirubin assay is simple, sensitive and without complex biolabeling.

Robust axion insulator and Chern insulator phases in a two-dimensional antiferromagnetic topological insulator.

The intricate interplay between non-trivial topology and magnetism in two-dimensional materials can lead to the emergence of interesting phenomena such as the quantum anomalous Hall effect. Here we investigate the quantum transport of both bulk crystal and exfoliated MnBi2Te4 flakes in a field-effect transistor geometry. For the six septuple-layer device tuned into the insulating regime, we observe a large longitudinal resistance and zero Hall plateau, which are characteristics of an axion insulator state. The robust axion insulator state occurs in zero magnetic field, over a wide magnetic-field range and at relatively high temperatures. Moreover, a moderate magnetic field drives a quantum phase transition from the axion insulator phase to a Chern insulator phase with zero longitudinal resistance and quantized Hall resistance h/e2, where h is Planck's constant and e is electron charge. Our results pave the way for using even-number septuple-layer MnBi2Te4 to realize the quantized topological magnetoelectric effect and axion electrodynamics in condensed matter systems.

Fluorescent sensing of free bilirubin at nanomolar level using a Langmuir-Blodgett film of glucuronic acid-functionalized gold nanoclusters.

Serum bilirubin is an important indicator to assess liver function and diagnose various types of liver diseases. The level of serum bilirubin is also negatively correlated with the risk of cardiovascular disease and cancer. We had fabricated a fluorescent film sensor aiming at free bilirubin detection at the nanomolar level. Gold nanoclusters capped by human serum albumin (HSA-AuNCs) were utilized as a fluorescent platform for bilirubin biorecognition. HSA-AuNCs were functionalized with glucuronic acid to increase the binding sites for bilirubin. An ultrathin film of glucuronic acid-functionalized gold nanoclusters was obtained by the Langmuir-Blodgett (LB) technique. When exposed to bilirubin, the interaction between free bilirubin and the functionalized AuNCs resulted in fluorescent quenching of the film. Good linearity could be achieved for the quenching efficiency versus the logarithm of free bilirubin concentration over a concentration range of 1.00 nM~5.00 µM. The limit of detection (LOD) was calculated to be (2.70 ± 0.14) × 10-1 nM (S/N = 3). The film sensor presents a good anti-interference capability towards common substances coexisting with bilirubin in serum. Satisfactory results achieved in the tests of real serum samples indicate that the LB film sensor can be used for bilirubin determination in nanomolar concentration.

TRICHOME AND ARTEMISININ REGULATOR 2 positively regulates trichome development and artemisinin biosynthesis in Artemisia annua.

Glandular secretory trichomes (GSTs) are regarded as biofactories for synthesizing, storing, and secreting artemisinin. It is necessary to figure out the initiation and development regulatory mechanism of GSTs to cultivate high-yielding Artemisia annua. Here, we identified an MYB transcription factor, AaTAR2, from bioinformatics analysis of the A. annua genome database and Arabidopsis trichome development-related genes. AaTAR2 is mainly expressed in young leaves and located in the nucleus. Repression and overexpression of AaTAR2 resulted in a decrease and increase, respectively, in the GSTs numbers, leaf biomass, and the artemisinin content in transgenic plants. Furthermore, the morphological characteristics changed obviously in trichomes, suggesting AaTAR2 plays a key role in trichome formation. In addition, the expression of flavonoid biosynthesis genes and total flavonoid content increased dramatically in AaTAR2-overexpressing transgenic plants. Owing to flavonoids possibly counteracting emerging resistance to artemisinin in Plasmodium species, AaTAR2 is a potential target to improve the effect of artemisinin in clinical therapy. Taken together, AaTAR2 positively regulates trichome development and artemisinin and flavonoid biosynthesis. A better understanding of this 'multiple functions' transcription factor may enable enhanced artemisinin and flavonoids yield. AaTAR2 is a potential breeding target for cultivating high-quality A. annua.

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers.

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water and how such structures change while being exposed to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property whereas other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.

Effect of immobilization site on the orientation and activity of surface-tethered enzymes.

Tethering peptides and proteins to abiotic surfaces has the potential to create biomolecule-functionalized surfaces with useful properties. Commonly used methods of immobilization lack control over the orientation in which biological molecules are covalently or physically bound to the surface, leading to sub-optimal materials. Here we use an engineered beta-galactosidase that can be chemically immobilized on a surface with a well-defined orientation through unique surface-accessible cysteine residues. A combined study using sum frequency generation (SFG) vibrational spectroscopy and coarse grained molecular dynamics (MD) simulations was performed to determine the effects of enzyme immobilization site and abiotic surface chemistry on enzyme surface orientation, surface coverage, and catalytic activity. Two beta-galactosidase variants that were immobilized through cysteine introduced at positions 227 and 308 were studied. In both cases, when the abiotic surface was made more hydrophilic, the enzyme surface coverage decreased, but the activity increased. MD simulations indicated that this is due to the weakened interactions between the immobilized enzyme and the more hydrophilic surface. These studies provide improved understanding of how enzyme-surface interactions can be optimized to maximize the catalytic activity of surface tethered enzymes.

Engineered Surface-Immobilized Enzyme that Retains High Levels of Catalytic Activity in Air.

In the absence of aqueous buffer, most enzymes retain little or no activity; however, "water-free" enzymes would have many diverse applications. Here, we describe the chemically precise immobilization of an enzyme on an engineered surface designed to support catalytic activity in air at ambient humidity. Covalent immobilization of haloalkane dehalogenase on a surface support displaying poly(sorbitol methacrylate) chains resulted in ∼40-fold increase in activity over lyophilized enzyme powders for the gas-phase dehalogenation of 1-bromopropane. The activity of the immobilized enzyme in air approaches 25% of the activity obtained in buffer for the immobilized enzyme. Poly(sorbitol methacrylate) appears to enhance activity by replacing protein-water interactions, thereby preserving the protein structure.

Engineering and Characterization of Peptides and Proteins at Surfaces and Interfaces: A Case Study in Surface-Sensitive Vibrational Spectroscopy.

Understanding molecular structures of interfacial peptides and proteins impacts many research fields by guiding the advancement of biocompatible materials, new and improved marine antifouling coatings, ultrasensitive and highly specific biosensors and biochips, therapies for diseases related to protein amyloid formation, and knowledge on mechanisms for various membrane proteins and their interactions with ligands. Developing methods for measuring such unique systems, as well as elucidating the structure and function relationship of such biomolecules, has been the goal of our lab at the University of Michigan. We have made substantial progress to develop sum frequency generation (SFG) vibrational spectroscopy into a powerful technique to study interfacial peptides and proteins, which lays a foundation to obtain unique and valuable insights when using SFG to probe various biologically relevant systems at the solid/liquid interface in situ in real time. One highlighting feature of this Account is the demonstration of the power of combining SFG with other techniques and methods such as ATR-FTIR, surface engineering, MD simulation, liquid crystal sensing, and isotope labeling in order to study peptides and proteins at interfaces. It is necessary to emphasize that SFG plays a major role in these studies, while other techniques and methods are supplemental. The central role of SFG is to provide critical information on interfacial peptide and protein structure (e.g., conformation and orientation) in order to elucidate how surface engineering (e.g., to vary the structure) can ultimately affect surface function (e.g., to optimize the activity). This Account focuses on the most significant recent progress in research on interfacial peptides and proteins carried out by our group including (1) the development of SFG analysis methods to determine orientations of regular as well as disrupted secondary structures, and the successful demonstration and application of an isotope labeling method with SFG to probe the detailed local structure and microenvironment of peptides at buried interfaces, (2) systematic research on cell membrane associated peptides and proteins including antimicrobial peptides, cell penetrating peptides, G proteins, and other membrane proteins, discussing the factors that influence interfacial peptide and protein structures such as lipid charge, membrane fluidity, and biomolecule solution concentration, and (3) in-depth discussion on solid surface immobilized antimicrobial peptides and enzymes. The effects of immobilization method, substrate surface, immobilization site on the peptide or protein, and surrounding environment are presented. Several examples leading to high impact new research are also briefly introduced: The orientation change of alamethicin detected while varying the model cell membrane potential demonstrates the feasibility to apply SFG to study ion channel protein gating mechanisms. The elucidation of peptide secondary structures at liquid crystal interfaces shows promising results that liquid crystal can detect and recognize different peptides and proteins. The method of retaining the native structure of surface immobilized peptides or proteins in air demonstrates the feasibility to protect and preserve such structures via the use of hydromimetic functionalities when there is no bulk water. We hope that readers in many different disciplines will benefit from the research progress reported in this Account on SFG studies of interfacial structure-function relationships of peptides and proteins and apply this powerful technique to study interfacial biomolecules in the future.

Glass capillary based microfluidic ELISA for rapid diagnostics.

Enzyme-linked immunosorbent assay (ELISA) is widely used in medical diagnostics and fundamental biological research due to its high specificity and reproducibility. However, the traditional 96-well-plate based ELISA still suffers from several notable drawbacks, such as long assay time (4-6 hours), burdensome procedures and large sample/reagent volumes (∼100 µl), which significantly limit traditional ELISA's applications in rapid clinical diagnosis and quasi-real-time prognosis of some fast-developing diseases. Here, we developed a user friendly glass capillary array based microfluidic ELISA device. Benefiting from the high surface-to-volume ratio of the capillary and the rapid chemiluminescent photo-imaging method with a commercial camera, our capillary based ELISA device significantly reduced the sample volume to 20 µL and shortened the total assay time to as short as 16 minutes (including detection time), which represent approximately 10-fold and 5-fold reduction in assay time and sample volume, respectively, in comparison with the traditional plate-based method. Furthermore, through the double exposure method, a nearly 10-fold increase in the detection dynamic range was achieved over the traditional well-based ELISA. Our device can be broadly used in rapid biochemical analysis for biomedicine and research/development laboratories.

Effect of Lipid Composition on the Membrane Orientation of the G Protein-Coupled Receptor Kinase 2-Gß1γ2 Complex.

Interactions between proteins and cell membranes are critical for biological processes such as transmembrane signaling, and specific components of the membrane may play roles in helping to organize or mandate particular conformations of both integral and peripheral membrane proteins. One example of a signaling enzyme whose function is dependent on membrane binding and whose activity is affected by specific lipid components is G protein-coupled receptor (GPCR) kinase 2 (GRK2). Efficient GRK2-mediated phosphorylation of activated GPCRs is dependent not only on its recruitment to the membrane by heterotrimeric Gßγ subunits but also on the presence of highly negatively charged lipids, in particular phosphatidylinositol 4',5'-bisphosphate (PIP2). We hypothesized that PIP2 may favor a distinct orientation of the GRK2-Gßγ complex on the membrane that is more optimal for function. In this study, we compared the possible orientations of the GRK2-Gßγ complex and Gßγ alone on model cell membranes prepared with various anionic phospholipids as deduced from sum frequency generation vibrational and attenuated total reflectance Fourier transform infrared spectroscopic methods. Our results indicate that PIP2 affects the membrane orientation of the GRK2-Gß1γ2 complex but not that of complexes formed with anionic phospholipid binding deficient mutations in the GRK2 pleckstrin homology (PH) domain. Gß1γ2 exhibits a similar orientation on the lipid bilayer regardless of its lipid composition. The PIP2-induced orientation of the GRK2-Gß1γ2 complex is therefore most likely caused by specific interactions between PIP2 and the GRK2 PH domain. Thus, PIP2 not only helps recruit GRK2 to the membrane but also "fine tunes" the orientation of the GRK2-Gßγ complex so that it is better positioned to phosphorylate activated GPCRs.

Influence of the side chain and substrate on polythiophene thin film surface, bulk, and buried interfacial structures.

The molecular structures of organic semiconducting thin films mediate the performance of various devices composed of such materials. To fully understand how the structures of organic semiconductors alter on substrates due to different polymer side chains and different interfacial interactions, thin films of two kinds of polythiophene derivatives with different side-chains, poly(3-hexylthiophene) (P3HT) and poly(3-potassium-6-hexanoate thiophene) (P3KHT), were deposited and compared on various surfaces. A combination of analytical tools was applied in this research: contact angle goniometry and X-ray photoelectron spectroscopy (XPS) were used to characterize substrate dielectric surfaces with varied hydrophobicity for polymer film deposition; X-ray diffraction and UV-vis spectroscopy were used to examine the polythiophene film bulk structure; sum frequency generation (SFG) vibrational spectroscopy was utilized to probe the molecular structures of polymer film surfaces in air and buried solid/solid interfaces. Both side-chain hydrophobicity and substrate hydrophobicity were found to mediate the crystallinity of the polythiophene film, as well as the orientation of the thiophene ring within the polymer backbone at the buried polymer/substrate interface and the polymer thin film surface in air. For the same type of polythiophene film deposited on different substrates, a more hydrophobic substrate surface induced thiophene ring alignment with the surface normal at both the buried interface and on the surface in air. For different films (P3HT vs. P3KHT) deposited on the same dielectric substrate, a more hydrophobic polythiophene side chain caused the thiophene ring to align more towards the surface at the buried polymer/substrate interface and on the surface in air. We believe that the polythiophene surface, bulk, and buried interfacial molecular structures all influence the hole mobility within the polythiophene film. Successful characterization of an organic conducting thin film surface, buried interfacial, and bulk structures is a first crucial step in understanding the structure-function relationship of such films in order to optimize device performance. An in-depth understanding on how the side-chain influences the interfacial and surface polymer orientation will guide the future molecular structure design of organic semiconductors.

The molecular interfacial structure and plasticizer migration behavior of "green" plasticized poly(vinyl chloride).

Tributyl acetyl citrate (TBAC), a widely-used "green" plasticizer, has been extensively applied in products for daily use. In this paper, a variety of analytical tools including sum frequency generation vibrational spectroscopy (SFG), coherent anti-Stokes Raman spectroscopy (CARS), contact angle goniometry (CA), and Fourier transform infrared spectroscopy (FTIR) were applied together to investigate the molecular structures of TBAC plasticized poly(vinyl chloride) (PVC) and the migration behavior of TBAC from PVC-TBAC mixtures into water. We comprehensively examine the effects of oxygen and argon plasma treatments on the surface structures of PVC-TBAC thin films containing various bulk percentages of plasticizers and the leaching behavior of TBAC into water. It was found that TBAC is a relatively stable PVC plasticizer compared to traditional non-covalent plasticizers but is also surface active. Oxygen plasma treatment increased the hydrophilicity of TBAC-PVC surfaces, but did not enhance TBAC leaching. However, argon plasma treatment greatly enhanced the leaching of TBAC molecules from PVC plastics to water. Based on our observations, we believe that oxygen plasma treatment could be applied to TBAC plasticized PVC products to enhance surface hydrophilicity for improving the biocompatibility and antibacterial properties of PVC products. The structural information obtained in this study will ultimately facilitate a molecular level understanding of plasticized polymers, aiding in the design of PVC materials with improved properties.

Highly coordinative molecular cobalt-phthalocyanine electrocatalyst on an oxidized single-walled carbon nanotube for efficient hydrogen peroxide production.

H2O2 production via the two-electron oxygen reduction reaction (2e- ORR) offers a potential alternative to the current anthraquinone method owing to its efficiency and environmental friendliness. However, it is necessary to determine the structures of electrocatalysts with cost-effectiveness and high efficiency for future industrialization demand. Herein, a supramolecular catalyst composed of cobalt-phthalocyanine on a near-monodispersed and oxidized single-walled carbon nanotube (CoPc/o-SWCNT) was synthesized via a solution self-assembly method for catalyzing the 2e- ORR for H2O2 electrosynthesis. Benefiting from the enhanced intermolecular interaction by introducing oxygen functional groups on o-SWCNTs, the oxidation states of single-atom Co sites were tuned via the formation of two extra Co-O bonds. Coupled with structural characterizations, density-functional theory (DFT) calculations reveal that the depressed d-band center of the Co site regulated by two axially-bridged O atoms gives rise to a suitable binding strength of oxygen intermediates (*OOH) to favor the 2e- ORR. Thus, the CoPc-6wt%/o-SWCNT-2 catalyst with optimized synthetic parameters delivers competitive 2e- ORR performance for H2O2 electrosynthesis in a neutral electrolyte (pH = 7), including enhanced H2O2 generation, satisfactory molar selectivity of ∼83-95% and long-period stability (75 h) in H-cell measurement. Moreover, it could also be boosted to show a high current of 45 mA cm-2, recorded turnover frequency of 25.3 ± 0.5 s-1 and maximum H2O2 production rate of 5.85 mol g-1 h-1 with a continuous H2O2 accumulation of 1.2 wt% in a flow-cell device, which outperformed most of the reported neutral-selective nonprecious metal single-atom catalysts.

Role of pattern recognition receptors in the development of MASLD and potential therapeutic applications.

Metabolic dysfunction-associated steatotic liver disease (MASLD) has become one of the most prevalent liver diseases worldwide, and its occurrence is strongly associated with obesity, insulin resistance (IR), genetics, and metabolic stress. Ranging from simple fatty liver to metabolic dysfunction-associated steatohepatitis (MASH), even to severe complications such as liver fibrosis and advanced cirrhosis or hepatocellular carcinoma, the underlying mechanisms of MASLD progression are complex and involve multiple cellular mediators and related signaling pathways. Pattern recognition receptors (PRRs) from the innate immune system, including Toll-like receptors (TLRs), C-type lectin receptors (CLRs), NOD-like receptors (NLRs), RIG-like receptors (RLRs), and DNA receptors, have been demonstrated to potentially contribute to the pathogenesis for MASLD. Their signaling pathways can induce inflammation, mediate oxidative stress, and affect the gut microbiota balance, ultimately resulting in hepatic steatosis, inflammatory injury and fibrosis. Here we review the available literature regarding the involvement of PRR-associated signals in the pathogenic and clinical features of MASLD, in vitro and in animal models of MASLD. We also discuss the emerging targets from PRRs for drug developments that involved agent therapies intended to arrest or reverse disease progression, thus enabling the refinement of therapeutic targets that can accelerate drug development.

γ-Ray Irradiation Significantly Enhances Capacitive Energy Storage Performance of Polymer Dielectric Films.

Polymer dielectric capacitors are fundamental in advanced electronics and power grids but suffer from low energy density, hindering miniaturization of compact electrical systems. It is shown that high-energy and strong penetrating γ-irradiation significantly enhances capacitive energy storage performance of polymer dielectrics. γ-irradiated biaxially oriented polypropylene (BOPP) films exhibit an extraordinarily high energy density of 10.4 J cm-3 at 968 MV m-1 with an efficiency of 97.3%. In particular, an energy density of 4.06 J cm-3 with an ultrahigh efficiency of 98% is reliably maintained through 20 000 charge-discharge cycles under 600 MV m-1. At 125 °C, the γ-irradiated BOPP film still delivers a high discharged energy density of 5.88 J cm-3 with an efficiency of 90% at 770 MV m-1. Substantial improvements are also achieved for γ-irradiated cycloolefin copolymers at a high temperature of 150 °C, verifying the strategy generalizability. Experimental and theoretical analyses reveal that the excellent performance should be related to the γ-irradiation induced polar functional groups with high electron affinity in the molecular chain, which offer deep energy traps to impede charge transport. This work provides a simple and generally applicable strategy for developing high-performance polymer dielectrics.

Fabrication-induced even-odd discrepancy of magnetotransport in few-layer MnBi2Te4.

The van der Waals antiferromagnetic topological insulator MnBi2Te4 represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBi2Te4 in the ground state. In this article, we demonstrate that fabrication can induce mismatched even-odd layer dependent magnetotransport in few-layer MnBi2Te4. We perform a comprehensive study of the magnetotransport properties in 6- and 7-septuple-layer MnBi2Te4, and reveal that both even- and odd-number-layer device can show zero Hall plateau phenomena in zero magnetic field. Importantly, a statistical survey of the optical contrast in more than 200 MnBi2Te4 flakes reveals that the zero Hall plateau in odd-number-layer devices arises from the reduction of the effective thickness during the fabrication, a factor that was rarely noticed in previous studies of 2D materials. Our finding not only provides an explanation to the controversies regarding the discrepancy of the even-odd layer dependent magnetotransport in MnBi2Te4, but also highlights the critical issues concerning the fabrication and characterization of 2D material devices.

Giant nonlocal edge conduction in the axion insulator state of MnBi2Te4.

The recently discovered antiferromagnetic (AFM) topological insulator (TI) MnBi2Te4 represents a versatile material platform for exploring exotic topological quantum phenomena in nanoscale devices. It has been proposed that even-septuple-layer (even-SL) MnBi2Te4 can host helical hinge currents with unique nonlocal behavior, but experimental confirmation is still lacking. In this work, we report transport studies of exfoliated MnBi2Te4 flakes with varied thicknesses down to the few-nanometer regime. We observe giant nonlocal transport signals in even-SL devices when the system is in the axion insulator state but vanishingly small nonlocal signal in the odd-SL devices at the same magnetic field range. In conjunction with theoretical calculations, we demonstrate that the nonlocal transport is via the helical edge currents mainly distributed at the hinges between the side and top/bottom surfaces. The helical edge currents in the axion insulator state may find unique applications in topological quantum devices.