Flexible, high-sensitivity, breathable strain sensors have great potential for application in wearable electronics. Existing wearable sensors are usually assembled with polymer encapsulation layers on thin-film substrates. The discomfort caused by low permeability and mechanical mismatch restricts people’s enthusiasm for selection. In this work, high-adhesion conductive graphite–carbon black composite inks were prepared using modified epoxy as the binding agent. Durable, breathable, and wearable strain sensors were successfully fabricated by dip-padding knitted fabrics with the conductive composite ink. The developed graphite composite sensor exhibits a broad tension sensing range (up to 20

Hydrogels do not have observable responses to external magnetic fields as they are conventionally thought to be diamagnetic. These materials require additives for magnetic control, limiting biomedical applications due to potential side effects. Here we show that calcium cations can induce strong paramagnetism of hydrogels rich in groups containing carbon-oxygen double bonds, including alginate, carboxymethyl chitosan, polyacrylamide and N-isopropyl acrylamide. Both experiments and computations reveal that the ubiquitous presence of net magnetic moments, the key to paramagnetism, is induced by the unexpected coupling of a single calcium cation and one carbonyl group under large calcium cation excess conditions. The paramagnetic phenomenon is also observed in the endogenous biomolecule sodium hyaluronate with calcium cations. We further demonstrate the applications of the strongly paramagnetic alginate-calcium hydrogel as a contrast agent in magnetic resonance imaging and a carrier in magnetic drug delivery. Our findings provide insights into the origin of magnetism and advance magnetism-related biomedical innovations.

The development of flexible, high-performance electrochemical biosensors for continuous and on-site monitoring of cholesterol is critical for advancing cardiovascular health diagnostics and personalized medicine. Here, we present a flexible MnO₂-modified screen-printed electrode (MnO₂/SPE) for cholesterol detection, where two-dimensional flower-like MnO₂ nanomaterials are used to functionalize the electrode surface. The MnO₂ nanocomposite significantly improves the electrochemical performance of the SPE by reducing interfacial impedance, optimizing charge transfer kinetics, and providing abundant active sites for electrocatalytic oxidation. The MnO₂/SPE sensor exhibits excellent analytical performance, including a wide linear range (1–160 μM), a low limit of detection (0.16 μM), and a high sensitivity of 0.197 μA·μM⁻¹·cm⁻². Notably, compressive mechanical strain (-1%) is demonstrated to further boost the sensing performance via the flexoelectric polarization effect, increasing the sensitivity to 0.2497 μA·μM⁻¹·cm⁻² and accelerating the electrocatalytic oxidation of cholesterol. The MnO₂/SPE sensor also shows good stability, reproducibility, and anti-interference capability, with all relative deviations below 5%. This work provides a new strategy to enhance the performance of flexible electrochemical sensors through strain engineering and demonstrates great potential for wearable cholesterol monitoring.

Two-dimensional MoS2 shows great promise for damage-resistant and adaptive functional devices owing to its intrinsic self-healing capability; however, phase-dependent damage and healing mechanisms remain unclear. Here, molecular dynamics simulations investigate the nano-indentation induced damage evolution and self-healing behavior of multilayer MoS2 with three phase structures (1T, 2H, and 3R). Load-depth response, interlayer sliding, displacement fields, crack propagation, maximum shear strain, and radial distribution functions reveal the underlying mechanisms. Results show that no cracks occur in the 1T phase, indicating excellent structural integrity. The 2H phase exhibits single-layer fracture or localized cracking, and no crack healing is observed in any of these cases. The 3R phase is prone to long strip-like cracks, most of which undergo partial healing. During healing, interlayer reconstruction induces edge dislocations and pronounced interlayer sliding, highly sensitive to the indenter radius. This study clarifies the phase-dependent damage and self-healing mechanisms of MoS2 at the atomic scale.

Two-dimensional (2D) nanostructured semiconductors with abundant active sites and specific surface area are promising non-precious metal catalysts for flexible electrochemical biosensors. Here, we reported the cost-effective and high-performance strain electrocatalytic uric acid (UA) sensors based on 2D Co3O4 nanosheets prepared by a simple hydrothermal method. The corresponding electrocatalytic efficiencies for UA were modulated by tensile and compressive strains. Moreover, density functional theory (DFT) calculations were performed to reveal the corresponding mechanisms from the atomic scale. The prepared UA strain sensor exhibits a wide detection concentration with a linear range from 6 mu M to 5 mM and a low detection limit of similar to 6 mu M. The induced compressive strain of -1.5 % in the 2D Co3O4 nanosheet significantly increases the sensitivity by 58.4 % and decreases the charge transfer impedance by 29.7 % of UA, while the tensile strain of + 1.5 % decreases the sensitivity by 52.4 % and increases the charge transfer impedance by 44.7 % of UA compared to those under zero strain. From DFT calculation, the corresponding compressive strain of -1.5 % decreases the spin-up band gap by 23.9 % and the spin-down band gap by 24.6 % and the tensile strain of + 1.5 % leads to the increase of 30.2 % in the spin-up band gap and 48.4 % in the spin-down band gap as to those of intrinsic zero strain. The decrease in bandgap leads to an increase in the electron transport rate, thus increasing the sensor sensitivity. Our research provides guidance on the design of low-cost and mass-producible 2D materials integrated into wearable high-performance electrocatalytic sensors.

Two-dimensional (2D) materials are widely used in heavy metal ion detection due to their high specific surface area and abundant active sites. Herein, we prepared highly selective and sensitive electrochemical sensors based on 2D graphitic-phase carbon nitride for the detection of Cu2+ and Pb2+ ions and investigated the effects of both tensile and compressive strains on the corresponding detection sensitivity, together with their mechanism. The prepared carbon nitride nanosheet sensors showed detection sensitivities of 3.63 and 0.41 mu Amu Mcm(-2), detection ranges of 0.2-100 and 6-100 mu M, and detection limits of 0.0033 and 0.23 mu M for Cu2+ and Pb2+, respectively. The induced compressive strain of -0.25% in the 2D CNNS significantly improved the sensitivity by 40.5% and 31.7%, while the tensile strain of +0.25% reduced the sensitivity by 41.9% and 43.9% in detecting Cu2+ and Pb2+ as compared to those at zero strain, respectively. Through DFT calculations, the corresponding compressive strain of -0.25% reduced the band gap from 1.21 eV under zero strain to 0.94 eV. On the contrary, the tensile strain of +0.25% increased the band gap from 1.21 to 1.45 eV, resulting from the contribution of orbitals of C-p and N-p. The declined and raised band gaps, respectively, result in increased and decreased electron transport rates, thereby improving and degrading the sensitivities of the sensors. Our research provides guidance on the design of flexible wearable sensors integrated into the construction of sensitive and reliable heavy ion detection systems.

The manipulation and mechanism of two-dimensional (2D) transition metal dichalcogenides (TMDs) by external electric field are significant to the photoelectric properties. Herein, the 2D MoS2 nanosheets were oxidized to form MoS2-MoO3 local heterojunctions by an electric field, applied in multistable memristors for the proposal of NanoQR code. A modified thermal oxidation model was derived to reveal the mechanism of local electric oxidation on 2D MoS2. From current-voltage curves, the barrier height of the MoS2 device showed an increase of 0.39 eV due to local oxidation after applying voltage for 480 s. Based on density-functional theory, the increase of barrier height was calculated as 0.38 eV between MoS2-MoS2 and MoS2-MoO(3 )supercells. The 2D MoS2-MoO3 local heterojunctions were further applied as multi- stable memory storage at the nanoscale. The findings suggest a novel strategy for controlling local electric oxidation on 2D TMDs to manipulate the properties for the application of photoelectric memory nanodevices.

The morphology and size control of anisotropic nanocrystals are critical for tuning shape-dependent physicochemical properties. Although the anisotropic dissolution process is considered to be an effective means to precisely control the size and morphology of nanocrystals, the anisotropic dissolution mechanism remains poorly understood. Here, usingin situliquid cell transmission electron microscopy, we investigate the anisotropic etching dissolution behaviors of polyvinylpyrrolidone (PVP)-stabilized Ag nanorods in NaCl solution. Results show that etching dissolution occurs only in the longitudinal direction of the nanorod at low chloride concentration (0.2 mM), whereas at high chloride concentration (1 M), the lateral and longitudinal directions of the nanorods are dissolved. First-principles calculations demonstrate that PVP is selectively adsorbed on the {100} crystal plane of silver nanorods, making the tips of nanorods the only reaction sites in the anisotropic etching process. When the chemical potential difference of the Cl-concentration is higher than the diffusion barrier (0.196 eV) of Cl-in the PVP molecule, Cl-penetrates the PVP molecular layer of {100} facets on the side of the Ag nanorods. These findings provide an in-depth insight into the anisotropic etching mechanisms and lay foundations for the controlled preparation and rational design of nanostructures.

Two-dimensional (2D) perovskites have been widely applied in photoelectric devices due to their excellent optical and electrical properties. However, the low optical absorption of their ultrathin thickness inhibits photoelectron generation and thus limits their performances. Herein, we constructed 2D CsPbBr3 devices of composite structures by combining them with g-C3N4 (CN) and graphene oxide (GO). As compared to CsPbBr3 devices, the photocurrents of GO/CsPbBr3 and CN/CsPbBr3 devices increase by 68 and 114%, respectively. Based on experimental spectra in combination with the finite-element method (FEM), the reflectivity values of GO/CsPbBr3 and CN/CsPbBr3 devices are, respectively, reduced by 21 and 33%, and therefore absorption coefficients are increased by 18 and 28%, respectively, and the corresponding internal quantum efficiencies are increased by 63 and 96%, respectively, in comparison to the CsPbBr3 devices. Furthermore, we have quantitatively determined the linear relationship between the absorption coefficient and the photocurrent based on the diffusion theory of semiconductors. A general approach for improving the optoelectronic performance can be extended to other devices by constructing composite structures with strong photon absorption and low reflection.

In summary, a free-standing MXene/CTS/Cu2O electrode was formed through electrostatic interaction of MXene and CTS with opposite charges, followed by the electrodeposition of Cu2O. Taking advantage of the synergistic function of MXene/CTS layers and Cu2O nanoparticles, this ternary electrode exhibits excellent sensing capabilities for glucose and cholesterol with preferable linear ranges that can cover the full concentration range in clinical diagnosis. For glucose sensing, the sensitivity was 60.295 µA·L/(mmol·cm2) with LOD being 52.4 µmol/L (SNR=3), while a sensitivity up to 215.71 µA·L/(mmol·cm2) and LOD low to 49.8 µmol/L (SNR=3) were achieved for cholesterol detection. Additionally, this biosensor possesses superior anti-interference ability and reproductivity, and thus exhibits great potential for genuine sample analysis. Accordingly, the as-prepared enzyme-free MXene/CTS/Cu2O electrode acts as a biomimetic electrocatalyst with excellent performance for analysis of multiple metabolites, and overcomes the disadvantages of an enzyme-based biosensor. This work has proposed a versatile strategy for designing and fabricating selfassembled nanocomposite materials with tuned structural and functional properties. It is a first attempt which could be easily integrated into portable electrochemical devices, facilitating effective routine monitoring of blood metabolites and paving the way for commercialization and point-of-care testing.

Solid–liquid–gas reactions are ubiquitous and are encountered in both nature and industrial processes1–4. A comprehensive description of gas transport in liquid and following reactions at the solid–liquid–gas interface, which is substantial in regard to achieving enhanced triple-phase reactions, remains unavailable. Here, we report a real-time observation of the accelerated etching of gold nanorods with oxygen nanobubbles in aqueous hydrobromic acid using liquid-cell transmission electron microscopy. Our observations reveal that when an oxygen nanobubble is close to a nanorod below the critical distance (~1 nm), the local etching rate is significantly enhanced by over one order of magnitude. Molecular dynamics simulation results show that the strong attractive van der Waals interaction between the gold nanorod and oxygen molecules facilitates the transport of oxygen through the thin liquid layer to the gold surface and thus plays a crucial role in increasing the etching rate. This result sheds light on the rational design of solid–liquid–gas reactions for enhanced activities. Real-time imaging of accelerated solid–liquid–gas reactions with nanobubbles uncovers the mechanisms of enhanced triple-phase reactions by identifying the critical distance between solid and gas at the nanoscale.

Two-dimensional (2D) CsPbBr3 have received great interest in flexible photoelectric devices due to their excellent carrier mobility and tunable optical bandgap. However, it is unknown if the piezo-phototronic effects of a vertically structured 2D CsPbBr3 photodetector affect its photoelectric performance. Herein, we fabricated a vertical structure device based on 2D CsPbBr3 by using conductive atomic force microscopy and then probed its photoelectric performances under different forces. The photocurrent and on/off ratio under 450 nm laser illumination rise by up to 2.1 and 5.3 times, respectively, when the applied force is 30 nN as compared with that under 10 nN. To investigate the mechanism underlying the enhancement of photoelectric performance, piezoelectric force microscopy measurement and density functional theory calculation were used to estimate the vertical piezoelectric coefficient of 2D CsPbBr3, which were found to be 7.3 pm/V and 3.8 pm/V, respectively. The enhancement of performances can be attributed to the piezo-phototronic effect of 2D CsPbBr3, which increases the separation of photogenerated holes at the interface. These findings propose a comprehensive strategy for enhancing photoelectric performance through piezo-phototronic effects in piezoelectric-based photoelectric devices with vertical structures.

Combining with in situ nanomechanical testing system and video module of scanning electron microscope, the nanoindentation testing is performed to study the peeling-tearing behavior of two-dimensional material van der Waals heterostructures. After two-dimensional MoS2 nanosheets prepared by chemical vapor deposition are assembled into MoS2/SiO2 heterostructures by wet transfer, the nanoindentation is carried out by manipulating the tungsten probe in the in situ nanomechanical testing system. When the tungsten probe is tightly indenting into MoS2 nanosheets, a new W/MoS2/SiO2 heterostructure is assembled. With the tungsten probe retracting, the adhesive effect makes the two-dimensional MoS2 nanosheet peel off from SiO2/Si substrate to form a bulge. After reaching a certain height, under the van der Waals adhesion interaction, an incomplete penetration fracture occurs along the arc line contacting the needle. Then cleavage appears and produces two strip cracks and MoS2/SiO2 interface separation takes place simultaneously, before a large area of MoS2 nanosheet is teared. Based on the density functional theory calculation of interface binding energy density of van der Waals heterogeneous interface, the interface binding energy density of MoS2/W is verified to be larger than that of MoS2 /SiO2, which explains the adhesion peeling behavior of MoS2 induced by van der Waals force between heterogeneous interfaces, perfectly. By using the peeling height and tearing length of MoS2 recorded by video module, the fracture strength of MoS2 is obtained to be 27.055 GPa and stress-strain relation can be achieved according to the film tearing model. The density functional theory simulation results show that the fracture strength of MoS2 is in a range of 21.7 -32.5 GPa, and the stress-strain relation is consistent with the experimental result measured based on film tearing model. The present work is expected to play an important role in measuring the fracture strengths of two-dimensional materials, the assembly, disassembly manipulation and reliability design of two-dimensional materials and van der Waals heterostructures devices.

Bimetallic Janus nanostructures (JNs) have attracted much interest because of their promising potential applications induced by unique interface effects, especially in catalysis. Catalytic stability acts a role as significant as catalytic efficiency in the potential applications of catalysts. However, the response of bi -metallic JNs to high temperature has been poorly investigated due to their complex structure and sub-limation kinetics. Herein, the thermal stability and sublimation mechanisms of CuAg JNs are studied through in situ annealing experiments performed in an aberration-corrected FEI Titan 80-300 transmission electron microscope operated at 300 kV. It is proven that CuAg JNs begin to sublimate until the temperature increases to 800 degrees C, although Ag nanostructures can always begin to sublimate at temperatures as low as 500 degrees C. Interestingly, Cu and Ag atoms sublimate simultaneously with a molar ratio likely to preserve at approximately 1 because Cu partially dissolves into the Ag phase at higher temperatures. Furthermore, a rational atomic motion mechanism is proposed to explain the phase transition in which the solid solution forms and the whole special sublimation process. These in situ observations promise to be helpful for understanding the evolutionary behaviors of bimetallic JNs under high temperatures arising in catalytic processes and other applications. (c) 2021 Published by Elsevier B.V.

Uniform silver nanostructures with specific geometrical morphologies, such as triangular and hexagonal nanoplates, often exhibit unique physicochemical properties with various potential applications. Despite the current progress in the liquid-phase synthesis of such Ag nanostructures, their growth mechanisms universally remain controversial due to the lack of direct visualization evidence at the nanoscale. Herein, by tracking the evolution trajectory of triangular nanoplates (TNPs) into hexagonal nanoplates (HNPs) in real-time using in situ liquid cell transmission electron microscopy, we reveal that the selective convex etching of chloride ions results in the suborbicular nanoplates (SNPs) as the intermediate shape, rather than the previously recognized truncated TNPs. Subsequently, the atomic-scale {111} stacking faults in TNPs as the driving force induce the side regrowth of the SNPs by the monomer attachment of Ag-0 atoms and the coalescence of preformed Ag clusters that were followed by atomic surface diffusion. Ag monomers preferentially redeposit to the {220} edges that grow rapidly out of existence, resulting in the formation of Ag HNPs with six {422} edges. The dissolution-regrowth evolution process found here sheds new light on the growth mechanisms of anisotropic Ag nanostructures with specific shapes. Our work not only demonstrates a potential route to the synthesis of Ag HNPs with controllable shapes and dimensions but also reveals the detailed nanoscale dissolution-regrowth mechanism during their formation, providing new insight for future rational design of controllable nanocrystal shapes.Y

Magnetic iron oxide nanoparticles have been proven to have versatile applications in biomedicine. Although numerous strategies have been developed to synthesize hydrophilic magnetic nanoparticles, there is still a challenge in the quantity and controllability of preparation of highly dispersible, stably water-dispersive magnetic nanoparticles. The current work presents a deep-eutectic solvent electrolysis to synthesize magnetic nanoparticles. In the electrolysis process, iron atoms at the anode electrode are oxidized to ferric ions, and then the ferric ions are combined with reactive oxygen species that derived from the decomposition of deep-eutectic solvents to form iron oxide nanocrystals. Concomitantly, hydrophilic radicals of amine groups produced by electrolyte decomposition are grafted on the particles. The monodisperse nanoparticle size ranged from 6 to 9 nm. The hydrophilic group loaded nanoparticles can be highly dispersed in water with neither surface post-modification nor organic stabilizers. The hydrodynamic particle diameter is between 20 and 30 nm. The transparent aqueous dispersions can be maintained for more than 600 days without precipitation.

We report the basal-plane catalytic reactivity of VS2 can be significantly enhanced by Mo doping for hydrogen evolution reaction (HER). Our optimal experiments reveal that the Tafel slope and overpotential at -10 mA cm(-2) of VS2 are reduced by 82.8% and 73.6% respectively after the Mo doping. Furthermore, the turnover frequency at 300 mV and electrochemical surface area of the optimal Mo-doped VS2 exhibit 19.2- and 27.2-fold enhancements compared with the pure VS2, together with significantly improved long-term cycle stability. Our density functional theory (DFT) calculations suggest that Mo dopant reduces the hydrogen adsorption free energy on S sites, and consequently strengthens the basal-plane activity. We uncover a charge transfer mechanism from Mo to the outer surface of S atoms, leading to the enhancement of p-orbital density of states of S at Fermi level and thus far super HER performance. Our findings provide a promising route and theoretical framework to improve the electrocatalytic HER performance of VS2, and may have general implications to other transition metal disulfides.

The pollution of water resource and shortage of clean water have become increasingly severe, developing an urgent demand of reliable, efficient yet low-cost material for everyday water purification. In the present work, a superhydrophobic paper tissue-based SiO2/PDMS composite has been prepared for both oil absorption and water-in-oil emulsion separation. The fabrication process is quite simple since it takes the full advantage of tissue that has naturally strong capillary force of which allows the material to absorb oil from water much more rapidly and completely (>99.9%) even under harsh conditions. The study has shown the novel material is exceptionally efficient in separating water-in-oil emulsion under gravity but no need of extraneous pressure. A variety of emulsions has been proven with high flux (>2,000 L m(-2) h(-1)) and high separation efficiency (>99.4%). It is believed that this study has proposed a highly reliable and efficient, low cost strategy in both oil absorption and water purification, which shed light on water treatment of both civil use and industry. (C) 2019 Elsevier Ltd. All rights reserved.

Solid-liquid-gas reactions are ubiquitous. An understanding of how gases influence the reactions at the nanoscale is significant for achieving the enhanced triple-phase reactions. Here, we report a real-time observation of the accelerated etching of gold nanorods with oxygen nanobubbles in aqueous hydrobromic acid using liquid cell transmission electron microscopy (TEM). Our observation reveals that when an oxygen nanobubble is close to a nanorod below the critical distance (~1nm), the local etching rate is significantly enhanced with over an order of magnitude faster. Molecular dynamics simulations results show that the strong attractive van der Waals interaction between the gold nanorod and oxygen molecules facilitates the transport of oxygen through the thin liquid layer to the gold surface and thus plays a crucial role in increasing the etching rate. This result sheds light on the rational design of solid-liquid-gas reactions for enhanced activities.

An understanding of nanocrystal shape evolution is significant for the design, synthesis, and applications of nanocrystals with surface-enhanced properties such as catalysis or plasmonics. Surface adsorbates that are selectively attached to certain facets may strongly affect the atomic pathways of nanocrystal shape development. However, it is a great challenge to directly observe such dynamic processes in situ with a high spatial resolution. Here, we report the anomalous shape evolution of Ag2O2 nanocrystals modulated by the surface adsorbates of Ag clusters during electron beam etching, which is revealed through in situ transmission electron microscopy (TEM). In contrast to the Ag2O2 nanocrystals without adsorbates, which display the near-equilibrium shape throughout the etching process, Ag2O2 nanocrystals with Ag surface adsorbates show distinct facet development during etching by electron beam irradiation. Three stages of shape changes are observed: a sphere-to-a cube transformation, side etching of a cuboid, and bottom etching underneath the surface adsorbates. We find that the Ag adsorbates modify the Ag2O2 nanocrystal surface configuration by selectively capping the junction between two neighboring facets. They prevent the edge atoms from being etched away and block the diffusion path of surface atoms. Our findings provide critical insights into the modulatory function of surface adsorbates on the shape control of nanocrystals.