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An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion ([Pb.sup.2+]) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to [Pb.sup.2+]and the use of DNA--Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for [Pb.sup.2+] is immobilized onto an Au electrode surface via a thiol--Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA--Au biobar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru[(N[H.sub.3]).sub.6.sup.3+], which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of [Pb.sup.2+] to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru[(N[H.sub.3]).sub.6.sup.3+] from the Au electrode surface. The release of Ru[(N[H.sub.3]).sub.6.sup.3+] results in lower electrochemical signal of Ru[(N[H.sub.3]).sub.6.sup.3+] confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru[(N[H.sub.3]).sub.6.sup.3+] provides quantitative measures of the concentrations of [Pb.sup.2+], with a linear calibration ranging from 5 nM to 0.1 [micro]M. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru[(N[H.sub.3]).sub.6.sup.3+], the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of [Pb.sup.2+] at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for [Pb.sup.2+]. Although this DNAzyme sensor is demonstrated for the detection of [Pb.sup.2+], it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

The recent synthesis of "borophane" polymorphs through hydrogenation has promoted the development of boron-based two-dimensional (2D) materials. In this work, the electronic structures and transport properties of hydrogenated borophene are investigated using first-principles calculations. The results show that the metallic character is preserved after hydrogenation, whereas electronic structures are greatly modulated by the position and number of introduced hydrogen atoms. More importantly, the presence of three-center-two-electron (3c-2e) bonds results in the formation of distorted Dirac points below the Fermi level in rect-1Hbridge and rect-2H borophane structures. The transport properties and the current–voltage (I–V) curve characters in those borophane structures can be efficiently modulated by the type of hydrogenations. Different hydrogenation patterns dominate diverse electronic transport behaviors. Such hydrogen atom-participant transport states endow borophane structures with potential applications in boron-based 2D electronics devices. [ABSTRACT FROM AUTHOR]

Host-guest chemistry is relevant to the development of microsensors to monitor pollutants. Coordination and host-guest chemistry is used in designing electrochemical sensors geared to detecting ammonium and alkali metal ions. Coordination complexes are used for the sensor molecules, and involve a functionalized tripodal ligand and a copper ion. Copper complexes function as efficient redox-active receptors since the electrochemical behavior shown when binding occurs with a guest is well-defined.

Spindle-like porous α-Fe2O3 was prepared from an iron-based metal organic framework (MOF) template. When tested as anode material for lithium batteries (LBs), this spindle-like porous α-Fe2O3 shows greatly enhanced performance of Li storage. The particle with a length and width of ∼0.8 and ∼0.4 μm, respectively, was composed of clustered Fe2O3 nanoparticles with sizes of <20 nm. The capacity of the porous α-Fe2O3 retained 911 mAh g–1 after 50 cycles at a rate of 0.2 C. Even when cycled at 10 C, comparable capacity of 424 mAh g–1 could be achieved. [ABSTRACT FROM AUTHOR]

Melanoma is a malignancy of the skin that is resistant to conventional treatment, necessitating the development of effective and safe new therapies. The percutaneous microneedle (MN) system has garnered increasing interest as a viable treatment option due to its high efficacy, minimal invasiveness, painlessness, and secure benefits. In this investigation, a sensitive MN system with multiple functions was created to combat melanoma effectively. This MN system utilized polyvinylpyrrolidone (PVP) as microneedle substrates and biocompatibility panax notoginseng polysaccharide (PNPS) as microneedle tips, which encapsulated PVP-stabilized CuO 2 nanoparticles as a therapeutic agent and disulfiram-containing F127 micelles to enhance the tumor treatment effect. The MN system had sufficient mechanical properties to pierce the skin, and the excellent water solubility of PNPS brought high-speed dissolution properties under the bio conditions, allowing the MNs to effectively penetrate the skin and deliver the CuO 2 nanoparticles as well as the drug-loaded micelles to the melanoma site. CuO 2 nanoparticles released by the MN system generated Cu 2+ and H 2 O 2 in the tumor acidic environment to achieve self-supply of hydrogen peroxide to chemodynamic therapy (CDT). In addition, Cu 2+ was chelated with disulfiram to produce CuET, which killed tumor cells. And the MN system had excellent near-infrared (NIR) photothermal properties due to the loading of CuO 2 nanoparticles and induced localized thermotherapy in the melanoma region to further inhibit tumor growth. Thus, the designed MN system accomplished effective tumor suppression and minimal side effects in vivo via combined therapy, offering patients a safe and effective option for melanoma treatment.

We investigate heterostructures composed of monolayer WSe 2 stacked on α-RuCl 3 using a combination of Terahertz (THz) and infrared (IR) nanospectroscopy and imaging, scanning tunneling spectroscopy (STS), and photoluminescence (PL). Our observations reveal itinerant carriers in the heterostructure prompted by charge transfer across the WSe 2 /α-RuCl 3 interface. Local STS measurements show the Fermi level is shifted to the valence band edge of WSe 2 which is consistent with p-type doping and verified by density functional theory (DFT) calculations. We observe prominent resonances in near-IR nano-optical and PL spectra, which are associated with the A-exciton of WSe 2 . We identify a concomitant, near total, quenching of the A-exciton resonance in the WSe 2 /α-RuCl 3 heterostructure. Our nano-optical measurements show that the charge-transfer doping vanishes while excitonic resonances exhibit near-total recovery in "nanobubbles", where WSe 2 and α-RuCl 3 are separated by nanometer distances. Our broadband nanoinfrared inquiry elucidates local electrodynamics of excitons and an electron-hole plasma in the WSe 2 /α-RuCl 3 system.

The breaking of the out-of-plane symmetry makes a two-dimensional (2D) Janus monolayer a new platform to explore the coupling between ferroelectricity and ferromagnetism. Using density functional theory in combination with Monte Carlo simulations, we report a novel phase-switchable 2D multiferroic material VInSe 3 with large intrinsic out-of-plane spontaneous electric polarization and a high Curie temperature ( T c ). The structural transition energy barrier between the two phases is determined to be 0.4 eV, indicating the switchability of the electric polarizations and the potential ferroelectricity. Carrier doping can boost the Curie temperature above room temperature, attributing to the enhanced magnetic exchange interaction. A transition from the ferromagnetic (FM) state to the antiferromagnetic (AFM) state can be induced by carrier doping in octahedra-VInSe 3 , while FM coupling is well-preserved in tetrahedron-VInSe 3 , which can be regulated to be either an XY or Ising magnet at an appropriate carrier concentration. These findings not only enrich the family of high -T c low-dimensional monolayers but also offer a new direction for the design and multifunctional application of multiferroic materials.

Previously, we successfully synthesized a 18 F-labeled positron-emission tomography (PET) tracer, termed 18 F-5-fluoro- N -(2-[diethylamino]ethyl)picolinamide ( 18 F-5-FPN), with high specificity for melanin. In this study, we sought to investigate the value of 18 F-5-FPN in assessing the response to photothermal therapy (PTT) in melanoma via comparison with 18 F-fluorodeoxyglucose ( 18 F-FDG) to reveal an early response, recognize early recurrence, and distinguish the inflammatory response during the treatment. B16F10, inflammatory, and MDA-MB-231 models were subjected to 18 F-FDG PET and 18 F-5-FPN PET static acquisitions. We compared quantitative data to assess the specificity of different agents for different diseases. B16F10 and MDA-MB-231subcutaneous tumor models were irradiated with an 808 nm laser for PTT. Their survival was documented to observe the efficacy of and response to PTT, using 18 F-5-FPN and 18 F-FDG PET. 18 F-5-FPN accumulated in B16F10 cell xenografts only, whereas 18 F-FDG accumulated in all three models. Melanin in B16F10 cell xenografts successfully transformed the optical energy into heat. Hematoxylin and eosin (H&E) staining at 24 h revealed destruction and extensive necrosis of tumor tissue. PTT rapidly inhibited the growth of B16F10 cell xenografts and prolonged the median survival. The mean tumor uptakes of 18 F-5-FPN on day 2 (7.52 ± 3.65 %ID/g) and day 6 (10.22 ± 6.00 %ID/g) were much lower than that before treatment (18.33 ± 4.98 %ID/g, p < 0.01). However, a significant difference in 18 F-FDG uptakes was not found between day 1 after PTT and before treatment. Compared with 18 F-FDG, 18 F-5-FPN PET could estimate PTT efficacy in melanoma, monitor minimal recurrence, and distinguish melanoma from inflammation and other carcinoma types, thanks to its high affinity to melanin. 18 F-5-FPN may provide a new approach for precise and accurate evaluation of response, timely management of therapeutic regimens, and sensitive follow-up.

MnBi 2 Te 4 is a van der Waals topological insulator with intrinsic intralayer ferromagnetic exchange and A-type antiferromagnetic interlayer coupling. Theoretically, it belongs to a class of structurally centrosymmetric crystals whose layered antiferromagnetic order breaks inversion symmetry for even layer numbers, making optical second harmonic generation (SHG) an ideal probe of the coupling between the crystal and magnetic structures. Here, we perform magnetic field and temperature-dependent SHG measurements on MnBi 2 Te 4 flakes ranging from bulk to monolayer thickness. We find that the dominant SHG signal from MnBi 2 Te 4 is unexpectedly unrelated to both magnetic state and layer number. We suggest that surface SHG is the likely source of the observed strong SHG, whose symmetry matches that of the MnBi 2 Te 4 -vacuum interface. Our results highlight the importance of considering the surface contribution to inversion symmetry-breaking in van der Waals centrosymmetric magnets.

Concerns about thermal safety and unresolved high-voltage stability have impeded the commercialization of high-energy lithium-ion batteries bearing LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathodes. Enhancing the cathode structure and optimizing the electrolyte formula have demonstrated significant potential in improving the high-voltage properties of batteries while simultaneously minimizing thermal hazards. The current study reports the development of a high-voltage lithium-ion battery that is both safe and reliable, using single-crystal NCM811 and a dual-salt electrolyte (DSE). After 200 cycles at high voltage (up to 4.5 V), the capacity retention of the battery with DSE was 98.80%, while that for the battery with a traditional electrolyte was merely 86.14%. Additionally, in comparison to the traditional electrolyte, the DSE could raise the tipping temperature of a battery's thermal runaway (TR) by 31.1 °C and lower the maximum failure temperature by 76.1 °C. Moreover, the DSE could effectively reduce the battery's TR heat release rate (by 23.08%) as well as eliminate concerns relating to fire hazards (no fire during TR). Based on material characterization, the LiDFOB and LiBF 4 salts were found to facilitate the in situ formation of an F- and B-rich cathode-electrolyte interphase, which aids in inhibiting oxygen and interfacial side reactions, thereby reducing the intensity of redox reactions within the battery. Therefore, the findings indicate that DSE is promising as a safe and high-voltage lithium-ion battery material.

In monolayer transition-metal dichalcogenide semiconductors, many-body correlations can manifest in optical spectra when electron-hole pairs (excitons) are photoexcited into a 2D Fermi sea of mobile carriers. At low carrier densities, the formation of charged excitons ( X ± ) is well documented. However, in WSe 2 monolayers, an additional absorption resonance, often called X - ', emerges at high electron density. Its origin is not understood. Here, we investigate the X - ' state via polarized absorption spectroscopy of gated WSe 2 monolayers in magnetic fields to 60T. Field-induced filling and emptying of the lowest optically active Landau level in the K ' valley causes repeated quenching of the corresponding optical absorption. Surprisingly, these quenchings are accompanied by absorption changes to higher Landau levels in both K ' and K valleys, which are unoccupied. These results cannot be reconciled within a single-particle picture, and demonstrate the many-body nature and intervalley correlations of the X - ' quasiparticle state.

van der Waals (vdW) magnets have emerged as a tunable platform for exploring a variety of layer-dependent magnetic phenomena. Here we probe the thickness-dependent magnetism of vanadium triiodide (VI 3 ), a material known as a layered ferromagnetic Mott insulator in its bulk form, using magnetic circular dichroism microscopy. Robust ferromagnetism is observed in all thin layers, down to the monolayer limit with large coercive fields. In contrast to known vdW magnets, the Curie temperature shows an anomalous increase as the layer number decreases, reaching a maximum of 60 K in monolayers. Second harmonic generation measurements reveal broken inversion symmetry in exfoliated flakes, down to trilayers. This observation demonstrates that the exfoliated flakes take a layer stacking arrangement that differed from the inversion-symmetric parent bulk counterpart. Our results suggest a coupling effect between magnetic and structural degrees of freedom in VI 3 and its potential for engineering layer and twist angle-dependent magnetic phenomena.

Recently, MnBi 2 Te 4 has been demonstrated to be an intrinsic magnetic topological insulator and the quantum anomalous Hall (QAH) effect was observed in exfoliated MnBi 2 Te 4 flakes. Here, we used molecular beam epitaxy (MBE) to grow MnBi 2 Te 4 films with thickness down to 1 septuple layer (SL) and performed thickness-dependent transport measurements. We observed a nonsquare hysteresis loop in the antiferromagnetic state for films with thickness greater than 2 SL. The hysteresis loop can be separated into two AH components. We demonstrated that one AH component with the larger coercive field is from the dominant MnBi 2 Te 4 phase, whereas the other AH component with the smaller coercive field is from the minor Mn-doped Bi 2 Te 3 phase. The extracted AH component of the MnBi 2 Te 4 phase shows a clear even-odd layer-dependent behavior. Our studies reveal insights on how to optimize the MBE growth conditions to improve the quality of MnBi 2 Te 4 films.

Direct optical probing of the antiferromagnetic order parameter in atomically thin samples is challenging, for example, via magneto-optical spectroscopy, due to the lack of net magnetization. Here, we report zigzag-antiferromagnetism (AFM) induced optical linear dichroism (LD) in layered transition-metal thiophosphate FePS 3 down to the monolayer limit. The observed LD is giant despite having the optical wave vector parallel to the Néel vector. The LD is at least one order of magnitude larger than those reported in other antiferromagnetic systems, where the optical wave vector is orthogonal to the Néel vector. The large LD enables the probe of 60° orientated zigzag-AFM domains. The optical anisotropy in FePS 3 originates from an electronic anisotropy associated with the zigzag direction of the AFM order and is independent of the spin-pointing direction. Our findings point to a new optical approach for the investigation and control of zigzag or stripe magnetic order in strongly correlated systems.

Lightweight polymeric foam is highly attractive as thermal insulation materials for energy-saving buildings but is plagued by its inherent flammability. Fire-retardant coatings are suggested as an effective means to solve this problem. However, most of the existing fire-retardant coatings suffer from poor interfacial adhesion to polymeric foam during use. In nature, snails and tree frogs exhibit strong adhesion to a variety of surfaces by interfacial hydrogen-bonding and mechanical interlocking, respectively. Inspired by their adhesion mechanisms, we herein rationally design fire-retardant polymeric coatings with phase-separated micro/nanostructures via a facile radical copolymerization of hydroxyethyl acrylate (HEA) and sodium vinylsulfonate (VS). The resultant waterborne poly(VS- co -HEA) copolymers exhibit strong interfacial adhesion to rigid polyurethane (PU) foam and other substrates, better than most of the current adhesives because of the combination of interfacial hydrogen-bonding and mechanical interlocking. Besides a superhydrophobic feature, the poly(VS- co -HEA)-coated PU foam can self-extinguish a flame, exhibiting a desired V-0 rating during vertical burning and low heat and smoke release due to its high charring capability, which is superior to its previous counterparts. Moreover, the foam thermal insulation is well-preserved and agrees well with theoretical calculations. This work offers a facile biomimetic strategy for creating advanced adhesive fire-retardant polymeric coatings for many flammable substrates.

Chromium iodide monolayers, which have different magnetic properties in comparison to the bulk chromium iodide, have been shown to form skyrmionic states in applied electromagnetic fields or in Janus-layer devices. In this work, we demonstrate that spin-canted solutions can be induced into monolayer chromium iodide by select substitution of iodide atoms with isovalent impurities. Several concentrations and spatial configurations of halide substitutional defects are selected to probe the coupling between the local defect-induced geometric distortions and orientation of chromium magnetic moments. This work provides atomic-level insight into how atomically precise chemical doping can be used to create and control complex magnetic patterns in chromium iodide layers and lays out the foundation for investigating the field- and geometric-dependent magnetic properties in similar two-dimensional materials., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The advent of two-dimensional (2D) magnets offers unprecedented control over electrons and spins. A key factor in determining exchange coupling and magnetic order is symmetry. Here, we apply second harmonic generation (SHG) to probe a 2D magnetic semiconductor CrSBr. We find that monolayers are ferromagnetically ordered below 146 K, an observation enabled by the discovery of a large magnetic dipole SHG effect in the centrosymmetric structure. In multilayers, the ferromagnetic monolayers are coupled antiferromagnetically, and in contrast to other 2D magnets, the Néel temperature of CrSBr increases with decreasing layer number. We identify magnetic dipole and magnetic toroidal moments as order parameters of the ferromagnetic monolayer and antiferromagnetic bilayer, respectively. These findings establish CrSBr as an exciting 2D magnetic semiconductor and extend the SHG probe of magnetic symmetry to the monolayer limit, opening the door to exploring the applications of magnetic-electronic coupling and the magnetic toroidal moment.

Moiré superlattices in van der Waals heterostructures are gaining increasing attention because they offer new opportunities to tailor and explore unique electronic phenomena. Using a combination of lateral piezoresponse force microscopy (LPFM) and scanning Kelvin probe microscopy (SKPM), we directly correlate ABAB and ABCA stacked graphene with local surface potential. We find that the surface potential of the ABCA domains is ∼15 mV higher (smaller work function) than that of the ABAB domains. First-principles calculations show that the different work functions between ABCA and ABAB domains arise from the stacking-dependent electronic structure. Moreover, while the moiré superlattice visualized by LPFM can change with time, imaging the surface potential distribution via SKPM appears more stable, enabling the mapping of ABAB and ABCA domains without tip-sample contact-induced effects. Our results provide a new means to visualize and probe local domain stacking in moiré superlattices along with its impact on electronic properties.

MnBi 2 Te 4 , a van der Waals magnet, is an emergent platform for exploring Chern insulator physics. Its layered antiferromagnetic order was predicted to enable even-odd layer number dependent topological states. Furthermore, it becomes a Chern insulator when all spins are aligned by an applied magnetic field. However, the evolution of the bulk electronic structure as the magnetic state is continuously tuned and its dependence on layer number remains unexplored. Here, employing multimodal probes, we establish one-to-one correspondence between bulk electronic structure, magnetic state, topological order, and layer thickness in atomically thin MnBi 2 Te 4 devices. As the magnetic state is tuned through the canted magnetic phase, we observe a band crossing, i.e., the closing and reopening of the bulk band gap, corresponding to the concurrent topological phase transition in both even- and odd-layer-number devices. Our findings shed new light on the interplay between band topology and magnetic order in this newly discovered topological magnet.