Disposable Peptidoglycan-Specific Biosensor for Noninvasive Real-Time Detection of Broad-Spectrum Gram-Positive Bacteria in Exhaled Breath Condensates.

Rapidly identifying and quantifying Gram-positive bacteria are crucial to diagnosing and treating bacterial lower respiratory tract infections (LRTIs). This work presents a field-deployable biosensor for detecting Gram-positive bacteria from exhaled breath condensates (EBCs) based on peptidoglycan recognition using an aptamer. Dielectrophoretic force is employed to enrich the bacteria in 10 s without additional equipment or steps. Concurrently, the measurement of the sensor's interfacial capacitance is coupled to quantify the bacteria during the enrichment process. By incorporation of a semiconductor condenser, the whole detection process, including EBC collection, takes about 3 min. This biosensor has a detection limit of 10 CFU/mL, a linear range of up to 105 CFU/mL and a selectivity of 1479:1. It is cost-effective and disposable due to its low cost. The sensor provides a nonstaining, culture-free and PCR-independent solution for noninvasive and real-time diagnosis of Gram-positive bacterial LRTIs.

Fish Scale for Wearable, Self-Powered TENG.

Flexible and wearable devices are attracting more and more attention. Herein, we propose a self-powered triboelectric nanogenerator based on the triboelectric effect of fish scales. As the pressure on the nanogenerator increases, the output voltage of the triboelectric nanogenerator increases. The nanogenerator can output a voltage of 7.4 V and a short-circuit current of 0.18 µA under a pressure of 50 N. The triboelectric effect of fish scales was argued to be related to the lamellar structure composed of collagen fiber bundles. The nanogenerator prepared by fish scales can sensitively perceive human activities such as walking, finger tapping, and elbow bending. Moreover, fish scales are a biomass material with good biocompatibility with the body. The fish-scale nanogenerator is a kind of flexible, wearable, and self-powered triboelectric nanogenerator showing great prospects in healthcare and body information monitoring.

Outstanding Energy Storage Performance of NBT-Based Ceramics under Moderate Electric Field Achieved via Antiferroelectric Engineering.

Ultrahigh energy-storage performance of dielectric ceramic capacitors is generally achieved under high electric fields (HEFs). However, the HEFs strongly limit the miniaturization, integration, and lifetime of the dielectric energy-storage capacitors. Thus, it is necessary to develop new energy-storage materials with excellent energy-storage densities under moderate electric fields (MEFs). Herein, the antiferroelectric material Ag0.9Ca0.05NbO3 (ACN) was used to modify the relaxor ferroelectric material 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 (NBT-SBT). The introduction of ACN results in high polarization strength, regulated composition of rhombohedral (R3c) and tetragonal (P4bm), nanodomains, and refined grain size. An outstanding recoverable energy density (Wrec = 4.6 J/cm3) and high efficiency (η = 82%) were realized under an MEF of 260 kV/cm in 4 mol % ACN-modified NBT-SBT ceramic. The first-principles calculation reveals that the interaction between Bi and O is the intrinsic mechanism of the increased polarization. A new parameter ΔP/Eb was proposed to be used as the figure of merit to measure the energy-storage performance under MEFs (∼200-300 kV/cm). This work paves a new way to explore energy-storage materials with excellent-performance MEFs.

Ultrahigh Energy-Storage Density of BaTiO3-Based Ceramics via the Interfacial Polarization Strategy.

Lead-free dielectric capacitors are excellent candidates for pulsed power devices. However, their low breakdown strength (Eb) strongly limits their energy-storage performance. In this study, Sr0.7Bi0.2TiO3 (SBT) and Bi(Mg0.5Hf0.5)O3 (BMH) were introduced into BaTiO3 (BT) ceramics to suppress interfacial polarization and modulate the microstructure. The results show that the introduction of SBT and BMH increases the band gap width, reduces the domain size, and, most importantly, successfully attenuates the interfacial polarization. Significantly enhanced Eb values were obtained in (1 - x)(0.65BaTiO3-0.35Sr0.7Bi0.2TiO3)-xBi(Mg0.5Hf0.5)O3 (BSBT-xBMH) ceramics. Meanwhile, the interfacial polarization was reduced to near zero in the sample with x = 0.10, achieving an ultrahigh Eb (64 kV/mm) and a very large recoverable energy-storage density (Wrec ≈ 9.13 J/cm3). In addition, the sample has excellent thermal stability (in line with EIA-X7R standards) and frequency stability. These properties indicate that the BSBT-0.10BMH ceramic holds promising potential for the application of pulsed power devices.

Enhanced Energy Harvesting Performance of Triboelectric Nanogenerators via Dielectric Property Regulation.

Triboelectric nanogenerators (TENGs) hold great application prospects and research values in the field of energy harvest. The friction layer of TENGs plays an important impact role in their output performance. Therefore, composition modulation of the friction layer is of great significance. In this paper, the xMWCNT/CS composite films with multiwalled carbon nanotubes (MWCNTs) as a filler and chitosan (CS) as a matrix were prepared and a TENG based on the xMWCNT/CS composite films (xMWCNT/CS-TENG) was constructed. The introduction of the conductive filler MWCNT significantly improves the dielectric constant of the films due to the Maxwell-Wagner relaxation. As a result, the output performance of the xMWCNT/CS-TENG is greatly enhanced. The best values of an open-circuit voltage of 85.8 V, a short-circuit current of 8.7 µA, and a transfer charge of 29 nC were obtained in the TENG with an optimum MWCNT content of x = 0.8 wt % under an external force of 50 N and a frequency of 2 Hz. The TENG can sensitively perceive human activities such as walking. Our results evidence that the xMWCNT/CS-TENG is a flexible, wearable, and eco-friendly energy collector, holding great prospects in health care and body information monitoring.

Enhanced Piezoelectricity and Thermal Stability of Electrostrain Performance in BiFeO3-Based Lead-Free Ceramics.

BiFeO3-based ceramics possess an advantage over large spontaneous polarization and high Curie temperature, and are thus widely explored in the field of high-temperature lead-free piezoelectrics and actuators. However, poor piezoelectricity/resistivity and thermal stability of electrostrain make them less competitive. To address this problem, (1 - x) (0.65BiFeO3-0.35BaTiO3)-xLa0.5Na0.5TiO3 (BF-BT-xLNT) systems are designed in this work. It is found that piezoelectricity is significantly improved with LNT addition, which is contributed by the phase boundary effect of rhombohedral and pseudocubic phase coexistence. The small-signal and large-signal piezoelectric coefficient (d33 and d33*) peaks at x = 0.02 with 97 pC/N and 303 pm/V, respectively. The relaxor property and resistivity are enhanced as well. This is verified by Rietveld refinement, dielectric/impedance spectroscopy and piezoelectric force microscopy (PFM) technique. Interestingly, a good thermal stability of electrostrain is obtained at x = 0.04 composition with fluctuation η = 31% (Smax'-SRTSRT×100%), in a wide temperature range of 25-180 °C, which is considered as a compromise of negative temperature dependent electrostrain for relaxors and the positive one for ferroelectric matrix. This work provides an implication for designing high-temperature piezoelectrics and stable electrostrain materials.

Humidity Sensing Properties of (In+Nb) Doped HfO2 Ceramics.

(In+Nb) co-doped HfO2 ceramics, Hf1-x(In0.5Nb0.5)xO2 (x = 0, 0.005, 0.05, and 0.1), were prepared via a solid-state reaction method. Dielectric measurements reveal that the environmental moisture has an obvious influence on the dielectric properties of the samples. The best humidity response was found in a sample with the doping level of x = 0.005. This sample was therefore selected as a model sample to further investigate its humidity properties. In doing so, nanosized particles of Hf0.995(In0.5Nb0.5)0.005O2 were fabricated via a hydrothermal method and the humidity sensing properties of this material were studied in the relative humidity range of 11-94% based on impedance sensor. Our results show that the material exhibits a large impedance change of nearly four orders of magnitude over the tested humidity range. It was argued that the humidity-sensing properties were related to the defects created by doping, which improves the adsorption capacity for water molecules.

Polarity Modulation Induced High Electrostrain Performance with Near-Zero Hysteresis in a (Sr0.7Bi0.2□0.1)TiO3-Based System.

High-precision piezo actuators necessitate dielectrics with high electrostrain performance with low hysteresis. Polarity-modulated (Sr0.7Bi0.2□0.1)TiO3-based ceramics exhibit extraordinarily discrete multiphase coexistence regions: (i) the relaxor phase coexistence (RPC) region with local weakly polar tetragonal (T) and pseudocubic (Pc) short-range polar nanodomains and (ii) the ferroelectric phase coexistence (FPC) region with T long-range domains and Pc nanodomains. The RPC composition features a specially high and pure electrostrain performance with near-zero hysteresis (S ∼ 0.185%, Q33 ∼ 0.038 m4·C-2), which is double those of conventional Pb(Mg1/3Nb2/3)O3-based ceramics. Particular interest is paid to the RPC and FPC with multiscale characterization to unravel local structure-performance relationships. Guided by piezoelectric force microscopy, scanning transmission electron microscopy, and phase-field simulations, the RPC composition with multiphase low-angle weakly polar nanodomains shows local structural heterogeneity and contributes to a flat local free energy profile and thus to nanodomain switching and superior electrostrain performance, in contrast to the FPC composition with a macroscopic domain that shows stark hysteresis. This work provides a paradigm to design high-precision actuator materials with large electrostrain and ultralow hysteresis, extending our knowledge of multiphase coexistence species in ferroelectrics.

Phase and Band Structure Engineering via Linear Additive in NBT-ST for Excellent Energy Storage Performance with Superior Thermal Stability.

Lead-free relaxor ferroelectric ceramics with ultrahigh energy-storage performance are vital for pulsed power systems. We herein propose a strategy of phase and band structure engineering for high-performance energy storage. To demonstrate the effectiveness of this strategy, (1 - x)(0.75Na0.5Bi0.5TiO3-0.25SrTiO3)-xCaTi0.875Nb0.1O3 (NBT-ST-xCTN, x = 0.1, 0.2, 0.3, 0.4, and 0.5) samples were designed and fabricated via the solid-state reaction method. The linear dielectric CTN was used as a modulator to tune both phase and band structures of the tested system. Our results show that both rhombohedral phase (R-phase) and tetragonal phase (T-phase) coexist in the samples. The R/T ratio decreases, while the band gap increases with increasing CTN content. The best energy-storage properties with large energy storage density (Wrec = 7.13 J/cm3), a high efficiency (η = 90.3%), and an ultrafast discharge time (25 ns) were achieved in the NBT-ST-0.4CTN sample with R/T = 0.121. Importantly, along with its excellent energy-storage performance, the sample exhibited superior thermal stability with the variations of Wrec ≤ 7% and η ≤ 10% over the wide temperature range of 233-413 K. This work suggests that this engineering of phase and band structures is a promising strategy to achieve superior energy-storage properties in lead-free ceramics.

Editorial for the Special Issue "Nanoscale Ferroic Materials-Ferroelectric, Piezoelectric, Magnetic, and Multiferroic Materials".

Ferroic materials, including ferroelectric, piezoelectric, magnetic, and multiferroic materials, are receiving great scientific attentions due to their rich physical properties [...].

Boosting the Humidity Performances of Na0.5BixTiO3 by Tuning Bi Content.

In the field of humidity sensors, a major challenge is how to improve the sensing performance of existing materials. Based on our previous work on Na0.5Bi0.5TiO3, a facile strategy of tuning the Bi content in the material was proposed to improve its sensing performance. Na0.5BixTiO3 (x = 0.3, 0.35, 0.4, 0.45) nanocomposites were synthesized by a hydrothermal method. Humidity sensing properties of these nanocomposites were investigated in the relative humidity range of 11% to 95%. Our results show that, compared to the sensor based on nominally pure sample (Na0.5Bi0.5TiO3), the sensor based on Na0.5Bi0.35TiO3 exhibits boosted sensing performance of excellent linear humidity response in the humidity range of 11-75% relative humidity, lower hysteresis value, and faster response/recovery time. The improvement of the sensing performance was argued to be the reason that the proper reduction in Bi content leads to a minimum value of oxygen-vacancy concentrations, thereby weakening the chemical adsorption but enhancing the physical adsorption. These results indicate that the proper underdose of the Bi content in Na0.5Bi0.5TiO3 can greatly boost the sensing performance.

Coupling Analysis on Microstructure and Residual Stress in Selective Laser Melting (SLM) with Varying Key Process Parameters.

With the application of Selective Laser Melting (SLM) technology becoming more and more widespread, it is important to note the process parameters that have a very important effect on the forming quality. Key process parameters such as laser power (P), scan speed (s), and scanning strategy (µ) were investigated by determining the correlation between the microstructure and residual stress in this paper. A total of 10 group 316L specimens were fabricated using SLM for comprehensive analysis. The results show that the key process parameters directly affect the morphology and size of the molten pool in the SLM deposition, and the big molten pool width has a direct effect on the larger grain size and crystal orientation distribution. In addition, the larger grain size and misorientation angle also affect the size of the residual stress. Therefore, better additive manufacturing grain crystallization can be obtained by reasonably adjusting the process parameter combinations. The transfer energy density can synthesize the influence of four key process parameters (P, v, the hatching distance (δ), and the layer thickness (h)). In this study, it is proposed that the accepted energy density will reflect the influence of five key process parameters, including the scanning trajectory (µ), which can reflect the comprehensive effect of process parameters more accurately.

Synergistic Piezo-Photocatalysis of BiOCl/NaNbO3 Heterojunction Piezoelectric Composite for High-Efficient Organic Pollutant Degradation.

Piezo-photocatalytic technique is a new-emerging strategy to alleviate photoinduced charge recombination and thus enhance catalytic performance. The heterojunction construction engineering is a powerful approach to improve photocatalytic performance. Herein, the BiOCl/NaNbO3 with different molar ratios piezoelectric composites were successfully synthesized by hydrothermal methods. The piezo/photodegradation rate (k value) of Rhodamine B (RhB) for BiOCl/NaNbO3 (BN-3, 0.0192 min-1) is 2.2 and 5.2 times higher than that of BiOCl (0.0089 min-1) and NaNbO3 (0.0037 min-1), respectively. The enhanced performance of BN-3 composite can be attributed to the heterojunction construction between BiOCl and NaNbO3. In addition, the piezo/photodecomposition ratio of RhB for BN-3 (87.4%) is 8.8 and 2.2 times higher than that of piezocatalysis (9.9%) and photocatalysis (40.4%), respectively. We further investigated the mechanism of piezocatalysis, photocatalysis, and their synergy effect of BN-3 composite. This study favors an in-depth understanding of piezo-photocatalysis, providing a new strategy to improve the environmental pollutant remediation efficiency of piezoelectric composites.

Humidity Sensitivity Behavior of CH3NH3PbI3 Perovskite.

The CH3NH3PbI3 (MAPbI3) powders were ground by PbI2 and CH3NH3I prepared by ice bath method. The humidity sensitive properties of an impedance-type sensor based on MAPbI3 materials were systematically studied. Our results indicate that the MAPbI3-based sensor has superior sensing behaviors, including high sensitivity of 5808, low hysteresis, approximately 6.76%, as well as good stability. Water-molecule-induced enhancement of the conductive carrier concentration was argued to be responsible for the excellent humidity sensitive properties. Interestingly, the humidity properties can be affected by red light sources. The photogenerated carriers broke the original balance and decreased the impedance of the sensor. This work promotes the development of perovskite materials in the field of humidity sensing.

Capacitive Aptasensor Coupled with Microfluidic Enrichment for Real-Time Detection of Trace SARS-CoV-2 Nucleocapsid Protein.

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has lasted for almost 2 years. Stemming its spread has posed severe challenges for clinical virus detection. A long turnaround time, complicated operation, and low accuracy have become bottlenecks in developing detection techniques. Adopting a direct antigen detection strategy, we developed a fast-responding and quantitative capacitive aptasensor for ultratrace nucleocapsid protein detection based on a low-cost microelectrode array (MEA) chip. Employing the solid-liquid interface capacitance with a sensitivity of picofarad level, the tiny change on the MEA surface can be definitively detected. As a result, the limit of detection reaches an ultralow level of femtogram per milliliter in different matrices. Integrated with efficient microfluidic enrichment, the response time of this sensor from the sample to the result is shortened to 15 s, completely meeting the real-time detection demand. Moreover, the wide linear range of the sensor is from 10-5 to 10-2 ng/mL, and a high selectivity of 6369:1 is achieved. After application and evaluation in different environmental and body fluid matrices, this sensor and the detection method have proved to be a label-free, real-time, easy-to-operate, and specific strategy for SARS-CoV-2 screening and diagnosis.

Li+ Selectivity of Carboxylate Graphene Nanopores Inspired by Electric Field and Nanoconfinement.

The regulation of the ion selectivity by electric field and ion association on the Li+ selectivity of carboxyl functionalized graphene nanopores are investigated by molecular dynamics simulation. Carboxylate graphene nanopores of sub-2 nm exhibit excellent Li+ selectivity under the electric field of 1.0 V nm-1 . The results show that ion association inspired by electric field may be a key factor affecting ion selectivity of sub-2 nm nanopores. The ion association of Mg2+ and Cl- can be promoted obviously near the nanopores under the electric field of 1.0 V nm-1 . The migrating of Mg2+ can be retarded by stable clusters of Mg2+ and Cl- formed near nanopores. The degree of association of Li+ with Cl- is relatively low and the disassociation of the Li+ cluster is easier so that Li+ can more easily pass through the nanopores. These results gain insight into the effect of ion association inspired by electric field and nanoconfinement of graphene nanopore on Mg2+ /Li+ separation, and provide helpful information for the application of nanoporous materials in extraction of Li+ ion from salt-lake brine.

TiO2/(K,Na)NbO3 Nanocomposite for Boosting Humidity-Sensing Performances.

Nanomaterials of TiO2, (K0.5Na0.5)NbO3, and the TiO2/(K0.5Na0.5)NbO3 nanocomposite were successfully synthesized by a hydrothermal method. Impedance-type humidity sensors were fabricated based on these materials. Our results reveal that the impedance of the TiO2/(K0.5Na0.5)NbO3 sensor changes by 5 orders of magnitude with an ultrahigh sensing response of Sf = 166 470 recorded at 100 Hz in the tested relative humidity (RH) range of 12-94%. This value is almost 2 and 4 orders of magnitude larger than that of the (K0.5Na0.5)NbO3 and TiO2 sensors, respectively. Interestingly, satisfactory response/recovery time (25/38 s, within 5 min), very small hysteresis (<5%), excellent stability, and good repeatability were also achieved in the TiO2/(K0.5Na0.5)NbO3 sensor. The improved sensing properties are ascribed to the synergistic effect of TiO2/(K0.5Na0.5)NbO3 heterojunction, which contributes the impedance that is susceptible to environmental humidity. This work underscores that it is a facile way to boost humidity-sensing performance by constructing proper nanocomposites.

Metastable oxygen vacancy ordering state and improved memristive behavior in TiO2 crystals.

Oxygen vacancy is one of the pivotal factors for tuning/creating various oxide properties. Understanding the behavior of oxygen vacancies is of paramount importance. In this study, we identify a metastable oxygen vacancy ordering state other than the well-known Magnéli phases in TiO2 crystals from both experimental and theoretical studies. The oxygen vacancy ordering is found to be a zigzag chain along the [0 0 1] direction in the (1 1 0) plane occurring in a wide temperature range of 200-500 °C. This metastable ordering state leads to a first-order phase transition accompanied by significant enhancement of dielectric permittivity and a memristive effect featuring a low driving electric field. Our results can improve oxide properties by engineering oxygen vacancies.

The Synergistic Effect Accelerates the Oxygen Reduction/Evolution Reaction in a Zn-Air Battery.

Perovskite oxides are promising electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to their abundance and high intrinsic catalytic activity. Here we introduce Ag into Sm0.5Sr0.5CoO3-δ (SSC) to form a Ag-SSC catalyst by ultrasonication and apply it as the air electrode for a Zn-air battery. It finds that the introduction of Ag into SSC can transform the Ag-SSC into a good bifunctional electrocatalyst toward ORR as well as OER. For instance, a more active half-wave potential with a value of 0.76 V for ORR is obtained at 1,600 rpm, while the OER overpotential is 0.43 V at I = 10 mA cm-2. Further characterization demonstrates that the improved catalyst activity of the Ag-SSC can be assigned to the synergistic effect generated between the Ag and SSC phases. The Zn-air battery with the Ag-SSC as an electrode not only gives a same discharge-charge voltage gap (1.33 V) with that of commercial Pt/C (1.33 V) but also presents an equivalent current efficiency (45.7% for Ag-SSC and 45.3% for Pt/C) at 10 mA cm-2. Moreover, the stability for 110 cycles is better. This result indicates that the Ag-SSC catalyst shows promise for use as a bifunctional electrocatalyst toward OER and ORR.

Microscopic insight into precipitation and adsorption of As(V) species by Fe-based materials in aqueous phase.

The mechanism of As(V) removal from the drinking water and industrial effluents by iron materials remains unclear at the molecular level. In this work, the association of Fe-based materials with As(V) species was explored using density functional theory and ab initio calculations. Solvent separated ion pair structures of [FeH2AsO4]2+aq species may be dominant in an acidic solution of FeAs complex. The association trend of H2AsO4- species by Fe3+aq is found to be quite weak in the aqueous solution, which may be attributed to the strong hydration of Fe3+aq and [FeH2AsO4]2+ species. However, the association of H2AsO4- species by colloidal clusters is quite strong, due to the weakened hydration of Fe(III) in colloidal structures. The hydrophobicity of Fe-based materials may be one of the key factors for their As(V) removal efficiency in an aqueous phase. When the number of OH- coordinated with Fe(III) increases, the association trend of As(V) by colloidal ferric hydroxides weakens accordingly. This study provides insights into understanding the coprecipitation and adsorption mechanisms of arsenate removal and revealing the high efficiency of arsenate removal by colloidal ferric hydroxides or iron salts under moderate pH conditions.