Bi-O Layers Research Articles

Nanocatalysis of silver-nanobioprobe based supersensitive electrochemical detection of Salmonella serotypes targeting virulence protein

Herein, we report a supersensitive and specific detection of Salmonella employing nanocatalysis of silver nanoparticle (AgNp). A nanobioprobe was developed employing specific antibody (Ab) that binds to a peptide present in transmembrane protein of Salmonella. We have studied 7 surface-exposed peptide hits from conserved virulence proteins (PagC, ST50, PagN, CdtB and FliC). These peptides were experimentally evaluated by BLI (Bio layer interferometry) for their reactivity towards antisera raised against an admix of major Salmonella serogroups. The most promising peptide was used to generate Ab with binding affinity Kd of 5.6 x 10-9 M. The Ab exhibited high specificity towards entire Salmonella serotypes prevalent in foods, as illustrated by the FACS (Fluorescence-activated cell sorting) study. The Ab-AgNp probe was blocked with a dual layer to prevent non-specific interactions, confirmed by employing BLI and TEM (Transmission electron microscopy). For the electrochemical detection, the autonanocatalysis of AgNp in presence of H2O2 was used to generate numerous Ag+ resulting in an amplified signal that could detect 10 cells/mL. The relative standard deviation (RSD) was observed to be 4.5%. The platform achieved recovery of 100-112% calculated for 102 cells/mL. The performance was validated in milk, buffer peptone water (BPW) and tap water by spiking studies. The study highlights the effectiveness of efficiently blocked AgNp-mediated probes for the highly selective and sensitive detection of Salmonella, representing a significant advancement in bacterial sensing.

Structural and phonon anomalies in the superconducting with varying doping level at high pressures

We examined the effect of the lattice compression on the crystal structure of the Bi2Sr2CaCu2 superconductor with nearly optimally doped and overdoped composition using X-ray diffraction technique. Our studies show that at high pressures (up to 30 GPa ) the doping level does not affect the crystal structure of this superconductor. Along with this, structural anomalies in ratio appear at a pressure that corresponds to that at which T c begins to decrease. This fact indicates a close connection between the observed anomalies and superconductivity. We also studied the effect of doping and pressure on the T c (P) and on the Raman active lattice modes of the Bi2Sr2CaCu2 superconductors. We find universal suppression of the T c by the pressure starting from the critical pressure P c in the range from 9 to 16 GPa, depending on the doping level of the Bi2Sr2CaCu2 samples. Concomitantly, we observe phonon anomalies around 10 to 20 GPa, which indicate possible pressure-induced charge redistribution in BiO layers. These newly detected anomalies may be related to the changes in the electronic structure which compete with the superconductivity.

Energy storage properties influenced by relaxor ferroelectric properties dependent on the growth direction of epitaxial Bi2SiO5 thin films

Ferroelectric Bi2SiO5 (BSO) thin films were deposited by pulsed laser deposition on Nb-doped (100), (110) and (111) SrTiO3 (Nb:STO) substrates, resulting in (001)-, (113)- and (204)-oriented epitaxial films. Due to the crystallinity of BSO, in which the Bi2O2 layers are formed perpendicular to the c-axis direction, the (001)-oriented epitaxial BSO thin film showed the lowest remanent polarization and the best leakage current characteristics. On the other hand, the (113)- and (204)-oriented films showed an increase in remanent polarization due to the improvement of a-oriented crystallinity. Through experiments using vertical and lateral piezoresponse force microscopy, it has been confirmed that the distribution of in-plane-oriented domains reducing remanent polarization decreases in the order of (001)-, (113)- and (204)-oriented epitaxial BSO thin films. The epitaxial BSO thin films that exhibit ferroelectric hysteresis loops similar to the relaxor ferroelectric thin films tended to have improved energy storage characteristics as a result of improved remanent polarization and saturation polarization. In particular, the (113)-oriented epitaxial BSO thin film showed a high recoverable energy density of about 41.6 J cm−3 and an energy storage efficiency of about 85.6%.

Absence of the impurity-resonance spot at a Bi defect located near the Zn impurity in Bi2Sr2Ca(Cu1-xZnx)2O8+δ

Zn dopants to Cu sites in high-Tc cuprates strongly suppress superconductivity and act as impurities with a strong quasiparticle scattering resonance. Using the scanning tunneling microscope, we investigate the electronic structure in the atomic scale around Zn impurities in Bi2Sr2Ca(Cu1-xZnx)2O8+δ. The intense scattering resonance of the Zn impurity in the CuO2 layer strongly affects the measured local density of states of the BiO layer on the surface. The pattern of the bound state induced by a Zn impurity consists of a central spot at the Bi atom just above the Zn impurity and eight symmetric spots at the next nearest neighboring (NNN) and the third nearest neighboring (3NN) sites of Bi atoms. When the Bi atom above the NNN Cu atom is missing, the corresponding scattering spot is absent simultaneously. Our results indicate that the measured impurity-induced bound state pattern is strongly influenced by Bi atoms on the surface and therefore supports the “filter” theoretical model of the nonlocal interlayer tunneling effect from the CuO2 layer to the BiO layer on the surface. Our research provides extra information about the impurity-induced bound state by Zn impurities.

Effects of La doping on diffused ferroelectric phase transition, electric and dielectric properties of lead-free SrBi2Ta2O9 ceramics

Citric acid-assisted method was used to synthesize pure polycrystalline La-doped SrBi2Ta2O9 powders which were uniaxially pressed and sintered under different conditions. La doping of SrBi2Ta2O9 resulted in the shortening of Ta-O bond lengths, but increased the unit cell volume and decreased the crystallite size. The effect of sintering process on dielectric properties was studied in order to find optimal sintering conditions. Dielectric loss, measured at room temperature, increases when sintering temperature rises from 1100 to 1200?C, as well as when sintering time increases from 6 to 9 h. Thus, further investigation was performed on the sample sintered at 1100?C for 6 h. The obvious change in ?? around TC and diffusive phase transition, pronounced for the ceramics with higher La content, were characteristic of the doped ceramics. The diffused ferroelectric phase transition behaviour is caused by structural disorder at the Sr-sites (Sr, Bi and La cations) in the Bi2O2 layers and perovskite blocks. The electrical conductivity increases steadily at lower temperatures (below 200 ?C), but shows a strong temperature- and frequency-dependent trend at higher frequencies. La-doping decreases conductivity by hindering charge carriers? long-distance mobility.

Mild chemistry synthesis of ultrathin Bi2O2S nanosheets exhibiting 2D-ferroelectricity at room temperature.

Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi2O2S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi2O2S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi2O2S nanosheets arises due to the local distortion of Bi2O2 layers, which destroys the local inversion symmetry of Bi2O2S.

Leakage current characteristics affected by crystallinity and domain wall current of epitaxial Bi5Ti3FeO15 thin films

We investigated leakage current characteristics affected by crystallinity and domain wall currents of epitaxial Bi5Ti3FeO15 (BTFO) thin films on Nb-doped SrTiO3 substrates. Highly a-oriented BTFO thin films, highly c-oriented BTFO thin films, and BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were prepared by controlling the substrate temperature and the pulsed laser deposition deposition rate. Highly c-oriented BTFO thin films exhibited the best leakage current characteristics because the Bi2O2 layers were placed perpendicular to the c-axis to reduce leakage currents. The BTFO thin films with a mixture of a-oriented and c-oriented crystallinity showed larger leakage currents compared to highly c-oriented BTFO thin films. The current domains of the BTFO thin films corresponding to the ferroelectric domain structures were observed by a conducting atomic force microscope, and it was observed that leakage currents were formed around the domain walls. In particular, the largest leakage currents are formed at the boundaries of c-oriented domains and a-oriented domains, and these domain boundaries confirmed that the BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were responsible for the largest leakage currents.

Leakage current characteristics of epitaxial Bi5Ti3FeO15 thin films affected by distribution of 90° domain walls with high conductivity

We investigated leakage current characteristics affected by crystallinity and domain wall currents of epitaxial BTFO thin films on Nb-doped SrTiO3 substrates. The c-oriented BTFO thin film and BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were prepared by controlling the substrate and PLD deposition rate. The c-oriented BTFO thin film exhibited the best leakage current characteristics because the Bi2O2 layers were placed perpendicular to the c-axis to reduce leakage currents. The BTFO thin films with a mixture of a-oriented and c-oriented crystallinity exhibited improved ferroelectric properties and piezoelectric properties compared to the c-oriented BTFO thin film. The current domains of the BTFO thin films corresponding to the ferroelectric domain structures were observed by a conducting atomic force microscope, and it was observed that leakage currents were formed around the domain walls. In particular, the largest leakage currents are formed at the boundaries of c-oriented domains and a-oriented domains, and these domain boundaries confirmed that BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were responsible for the largest leakage currents.

Discovery of a Superconductor Bi5 O4 S3 Cl Containing the Unique BiS3 Layer.

The BiS2 -based layered superconductors with structures similar to those of cuprates and iron-based superconductors have stimulated much research interest. Here, a new quaternary compound is reported, Bi5 O4 S3 Cl, which crystalizes in a tetragonal structure with P4/mmm (No. 123) space group having alternately stacking unique BiS3 layers and Bi2 O2 layers along the c-axis with a Cl atom located at the center of the unit cell. A superconducting transition above 3 K is observed for both electrical transport and magnetic measurements. Hall resistivity measurements show its multiband character with a conduction dominated by electron-like charge carriers. The first-principles calculations exhibit that the semiconducting parent phase Bi5 O4 S3 Cl becomes metallic when sulfur vacancies are introduced, which hints the origin of superconductivity in Bi5 O4 S3 Cl. The findings will inspire the exploration of new BiS-based superconductors.

Effect of surface Se concentration on stability and electronic structure of monolayer Bi2O2Se

Structural stability is one of the most fundamental issues to explore the applications of two-dimensional (2D) materials. Se-terminated bismuth oxychalcogenide, Bi2O2Se, attracts extensive attention as its quasi-2D nature, which links traditional three-dimensional (3D) and van de Waals 2D materials. Herein, we systematically constructed Bi2O2Se monolayers with different surface Se concentrations and studied their structural stability under different chemical environments. The stability of Bi2O2Se monolayer is found to be sensitive to the surface Se concentration, i.e., its formation energy decreases linearly until the Se concentration increases to 50% and then remains flat. Five monolayers with 0%, 12.5%, 50%, 87.5% and 100% Se concentrations are found to be highly stable at different chemical environments from Se-poor to Se-rich. Among them, the 50% Se concentration is high-symmetry with a neat BiO layer sandwiched between two Se layers, showing a direct-gap semiconducting nature. Structural deformation occurs in the other four Se concentrations, resulting in a p-type semiconductor characteristic with in-gap states. Scanning tunneling microscope simulations characterize the arrangement of atoms on the surfaces, and reflect the distribution of the local electronic structure. Our work is expected to provide further insight into the stability of Bi2O2Se monolayers and advance the understanding on other quasi-2D materials.

Active ion-exchangeable Bi2O(OH)2SO4 synthesized by ball milling for effective iodine enrichment: Insight into the pathway

Effective capture of radioactive iodine and iodine enrichment from dilute source are highly desirable but still remain as significant challenges. Based on mechanochemical activation of Bi oxide (Bi2O3) toward iodine incorporation by forming BiOI, we report a new approach to functionalize Bi2O3 with several anion groups just by simply co-milling with Bi sulfate. Several analytical methods were used to characterize the reaction products and its high efficiency for iodine enrichment inside. Compared with activation just for α-Bi2O3 itself, formation of Bi2O(OH)2SO4 was confirmed to allow a tremendous increase in adsorption capacity up to 335.57 mg/g towards iodine with the product, due to effect by ion-exchange with three anion groups (SO42−, CO32−, OH−) to form BiOI with a stable structure of Bi-O layer, demonstrating obvious advantages as a newly developed typical anionic adsorbent. Iodine can be recovered by heating BiOI to give back Bi2O3 for recycling. As a cost-effective and environmental-friendly process to produce an efficient material for iodine enrichment, this research may open a promising way to effectively remove radioactive iodine and recover iodine resources.

A highly sensitive Nano Gap Embedded AlGaN/GaN HEMT sensor for Anti-IRIS antibody detection

This study investigates the feasibility of Nano gap embedded AlGaN/GaN HEMT to sense antibody-antigen reaction. The sensor can detect the binding response of a typical antibody Ixodes ricinus immunosuppressor (anti-Iris) protein in Nano cavity. The sensor performance is analyzed by the change in electrical characteristics by the anti-iris antibody and iris antigen interaction. The device performance is optimized independently by varying cavity thickness, cavity length, biomolecule length, and Al composition. The output drain current recorded at VDS = 10V was linearly incremented with the length of the bio layers. The increase in cavity thickness and length will reduce the sensitivity due to a reduction in the cavity fill-in factor. The maximum sensitivity obtained is 169% at a cavity thickness of 10 nm and cavity length of 100 nm with 30% Al content. Silvaco Atlas simulation software has simulated and optimized the proposed device structure.

Isolation of alpaca-derived single-domain antibodies against zika virus non-structural proteins to interrogate viral replication

Abstract Zika virus (ZIKV) is a re-emergent flavivirus that triggered a global health emergency from 2015 to 2017. ZIKV and other impactful flaviviruses, including dengue virus, lack the antiviral treatments and vaccines needed to diminish their threat to communities world-wide. This is in part due to gaps in our understanding of the flavivirus lifecycle; despite numerous investigations into flavivirus non-structural (NS) protein function. I hope to forge a deeper understanding of crucial NS protein functions and interactions throughout the ZIKV replication cycle. I will use alpaca-derived variable heavy-chain-only (VHH) antibody fragments, isolated from an alpaca immunized with ZIKV NS proteins, to perturb the replication cycle and therefore identify key NS protein epitopes used during replication. I individually purified NS1, NS2b, NS3, NS4b, NS5 for use in alpaca immunization, phage display panning, and enzyme-linked immunosorbent assays (ELISAs). From the alpaca peripheral blood I isolated RNA and amplified VHH genes, enriched for NS-protein binders with iterative phage display, and screened potential high binders via ELISA. I have isolated VHH sequences that interact with the ZIKV helicase, NS3, and the RNA-dependent RNA polymerase, NS5. I plan to purify each VHH and express them in ZIKA-permissive A549 cells as stable lines. Using purified VHH, I will analyze their binding ability in-vitro by ELISA and bio layer interferometry, and quantify in-vitro inhibition of NS3 protease and helicase activity for NS3 binders, and NS5 polymerase and methyltransferase activity. With the stable cells lines I will investigate each VHHs ability to impede ZIKV virus production and formation of replication complexes in infected cell lines. Support from training grant "Interactions at the Microbe-Host Interface" T32AI007472

Understanding the piezoelectric origin of bismuth layer-structured ferroelectric polycrystal using first-principle method

Polycrystalline ferroelectric piezoelectric materials are widely used in various functional electronic devices. We present a systematic orientational average method to estimate the piezoelectric properties of ferroelectric polycrystals via first-principle calculations. This method can construct a bridge to connect the monocrystalline and polycrystalline ferroelectric piezoelectric materials, which opens a door to estimate the piezoelectric properties of polycrystals via first-principle calculations, helping the further study of piezoelectric polycrystals. The piezoelectric properties of bismuth layer-structured ferroelectrics (BLSFs) polycrystals are investigated via the method, which presents a good agreement in other theoretical and experimental results. It is found that the longitudinal polarization stretching and in-plane polarization rotation contribute the most of piezoelectricity for poled polycrystals. Unexpected polarization stretching of Bi2O2 layer and slipping between Bi2O2 layer and perovskite block are revealed, being considered to play an important role for the piezoelectricity of BLSFs.

Existence of two-dimensional hole gas at the interface of Bi(Zn, Ti)O[formula omitted]/SrTiO[formula omitted] heterostructures: An ab-initio study

We present first-principles calculations for a system consisting of a varying number of layers of the ferroelectric semiconductor Bi(Zn, Ti)O3 (BZT) on top of SrTiO3 (STO) substrate. To begin with, we assume that a TiO2 layer in STO is connected to a BiO layer in BZT. We show that atomic relaxation has a significant effect on the electronic properties of the heterostructure. In the absence of relaxation, due to the large polarization in BZT, a two-dimensional electron gas is formed at the interface when one unit cell of BZT is placed on top of STO. When relaxation is taken into account, the polarization in BZT is reduced in value and reversed in direction; in this case the insulator-to-metal transition occurs when the number of BZT unit cells reaches four, and a two-dimensional hole gas is formed at the interface. We also consider the case where an SrO layer in STO connects to a (Zn, Ti)O2 layer in BZT, and show that, when three unit cells of BZT are added on top of STO, a two-dimensional electron gas is formed near the interface.

Wearable sensors made with solution-blow spinning poly(lactic acid) for non-enzymatic pesticide detection in agriculture and food safety

On-site monitoring the presence of pesticides on crops and food samples is essential for precision and post-harvest agriculture, which demands nondestructive analytical methods for rapid, low-cost detection that is not achievable with gold standard methods. The synergy between eco-friendly substrates and printed devices may lead to wearable sensors for decentralized analysis of pesticides in precision agriculture. In this paper we report on a wearable non-enzymatic electrochemical sensor capable of detecting carbamate and bipyridinium pesticides on the surface of agricultural and food samples. The low-cost devices (<US$ 0.08 per unit) contained three-electrode systems deposited via screen-printing technology (SPE) on solution-blow spinning mats of poly (lactic acid) (PLA). The flexible PLA/SPE sensors can be used on flat, curved and irregular surfaces of leaves, vegetables and fruits. Detection was performed using differential pulse voltammetry and square wave voltammetry with detection limits of 43 and 57 nM for carbendazim and diquat, respectively. The wearable non-enzymatic sensor can discriminate and quantify carbendazim and diquat on apple and cabbage skins with no interference from other pesticides. The use of such wearable sensors may be extended to other agrochemicals, including with incorporation of active bio (sensing) layers for online monitoring of any type of agricultural products and foods.

Bi4AO6Cl2 (A = Ba, Sr, Ca) with Double and Triple Fluorite Layers for Visible-Light Water Splitting.

Layered oxyhalides containing double or triple fluorite layers are promising visible-light-responsive water-splitting photocatalysts with unique band structures. Herein, we report on the synthesis, structure, and photocatalytic property of Bi4BaO6Cl2 (I4/mmm) with alternating double (Bi2O2) and triple (Bi2BaO4) fluorite layers, which was extracted from the crystallographic database on the basis of Madelung potential calculations. Rietveld refinements from powder X-ray and neutron diffraction data revealed the presence of cationic disorder between Bi2O2 and Bi2BaO4 layers, leading to electrostatic stabilization. DFT calculations suggested that photogenerated electrons and holes flow through the double and triple layers, respectively, which may suppress electron-hole recombination. We expanded this double-triple system to include Bi4CaO6Cl2 and Bi4SrO6Cl2 with orthorhombic distortions and different degrees of cationic disorder, which allow band gap tuning. All the double-triple compounds Bi4AO6Cl2 showed stable water-splitting photocatalysis in the presence of a sacrificial reagent.

Structure-property relationships in the lanthanide-substituted PbBi2Nb2O9 Aurivillius phase synthesized by the molten salt method

Samples of PbBi2Nb2O9, PbBi1.5La0.5Nb2O9, and PbBi1.5Nd0.5Nb2O9 have been prepared by the molten salt method. The structure, morphology, and electrical properties were investigated. All samples are single-phase and crystallize in an orthorhombic structure with A21am symmetry. Neutron diffraction data indicate that the Ln3+ cations prefer to occupy the perovskite A-site, whereas Pb/Bi occupy the perovskite A-site and the Bi2O2 layer. Changes in unit cell volume are observed on substitution and are attributed to the ionic radii of the Ln3+ cations and also correlated to changes in the B-O bond distances in the BO6 octahedra, which are also observed in IR spectra. SEM images reveal anisotropic plate-like grains, which increase in size with the presence of Ln3+ ions. The ferroelectric transition temperature (Tc) decreases with decreasing degree of BO6 distortion as the influence of the 6s2 lone pair of Bi3+ is diminished. Relaxor ferroelectric behavior is observed with Ln3+ substitution, driven by the disorder of the A-site cations. The room temperature ferroelectric polarization increases with Ln3+ substitution, ascribed to the decreased dielectric loss.

Unexpected Photoinduced Room Temperature Magnetization in Bi2 WO6 Nanosheets.

The current investigation in magnetism in 2D materials offers new opportunities for studying spintronics at low dimensions. Here, reversible photoinduced room temperature magnetization in 2D Bi2 WO6 nanosheets is reported for the first time. Compared with the original state, the ultraviolet (UV)-illuminated Bi2 WO6 nanosheets show a yellow-green color change and significantly enhanced magnetic signals (saturated magnetization (Ms ) increased from 0.002 to 0.12 emu g-1 ). X-ray photoelectron spectroscopy (XPS) results show unexpected W reduction (W6+ to W5+ /W4+) and Bi oxidation (Bi3+ to Bi5+ ) upon UV illumination for the Bi2 WO6 nanosheets, indicating a photoexcited Bi to W charge transfer. Density functional theory (DFT) calculations indicate spontaneous spin polarization of the Bi2 WO6 nanosheets in the excited metastable state. Meanwhile, thicker Bi2 WO6 nanoplates or nanoparticles show no enhanced magnetic signals upon UV illumination. UV illumination of the thin Bi2 WO6 nanosheets can induce the formation of internal electric field (polarization), leading to structural deformation/lattice distortion (photostriction). The photoexcited electrons are trapped in the WO6 layers while the photogenerated holes are trapped in the Bi2 O2 layers, leading to spin polarization and enhance the magnetization. The research may bring some new insights in tuning the magnetic properties of 2D nanostructures.

Coupling ferroelectric polarization and anisotropic charge migration for enhanced CO2 photoreduction

CO2 photoreduction into solar fuels is promising for generating renewable energy. Herein, SrBi2Nb2O9 nanosheets are prepared as high-performance photocatalysts for CO2 reduction, highlighting superiority of ferroelectric polarization and anisotropic charge migration. Ferroelectric polarization within SrBi2Nb2O9 nanosheets provides an in-built electric field, which greatly facilitates the bulk charge separation. Also, the photogenerated electrons and holes migrate separately to the NbO6 octahedral layers and within the ab-plane in the Bi2O2 layers, achieving efficient anisotropic charge migration. Without co-catalyst or sacrificial agent, SrBi2Nb2O9 nanosheets show outstanding CO2 reduction activity in producing CH4. The ferroelectric polarization is further enhanced by electric poling and annealing post-treatments. The electrically poled SrBi2Nb2O9 shows a high CH4 evolution rate of 25.91 μmol g−1 h−1 with an AQE of 1.96 % at 365 nm, exceeding most of state-of-the-art photocatalysts reported to date. This work paves an avenue for development of highly efficient photocatalysts and beyond by tuning the ferroelectricity and electronic structure.