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1.
Nanotechnology ; 31(15): 155401, 2020 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-31855853

RESUMO

Electrode materials that can function well in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) are desirable for electrochemical energy storage applications, especially under high rate. In this work, a three-dimensional (3D) mesoporous γ-Fe2O3@carbon nanofiber (γ-Fe2O3@CNF) mat has been successfully synthesized by sol-gel based electrospinning and carbonization. It delivers a specific capacity of 820 mAh g-1 at 0.5 C after 250 cycles, 430 mAh g-1 at 6 C after 1000 cycles, and 222 mAh g-1 at ultrahigh rate of 60 C for LIBs, while for SIBs it delivers a specific capacity of 360 mAh g-1 at 1 C after 1000 cycles and 130 mAh g-1 at 60 C. Besides, the result of ex situ microstructure examination shows the polycrystalline nature of γ-Fe2O3 nanoparticle still exists in LIB even after 1000 cycles, while it vanishes in SIB, suggesting that the relatively larger volume expansion occurred during Na+ insertion/deinsertion, resulting in pulverization of the particles. The CNFs maintained their pristine 3D network structure after the charge/discharge, which demonstrated the critical role of a robust conductive electrode in promoting fast Li+/Na+ transportation. More importantly, they act as an electrical bridge between Li+/Na+ and γ-Fe2O3 nanoparticles, therefore suppressing the cell impedance growth and γ-Fe2O3 volume expansion, resulting in the enhancement in both cyclic and rate capability.

2.
J Am Chem Soc ; 141(50): 19715-19727, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31763827

RESUMO

Despite the many attempts to build ultrathin 2D-2D heterojunctions via wet chemical methods, the resulting composite materials reported to date suffer from poor interfacial bonding and/or complexity of the synthetic protocols. Encouraged by the structural compatibility of Bi2WO6 and Bi2O2S, both of which are 2D semiconductors sharing a rather similar structural unit of a [Bi2O2]2+ slice in their crystal structures, we have successfully fabricated an ultrathin nanosheet with a tightly bonded 2D-2D heterojunction between the two components by facilely joining the [Bi2O2]2+ and [S]2- slices using a simple two-step hydrothermal method. Such a Bi2WO6-Bi2O2S 2D-2D heterojunction has a five-alternating-layer (Bi2O2S-Bi2WO6-Bi2O2S-Bi2WO6-Bi2O2S) sandwich structure and a thickness down to ca. 5 nm and was obtained by simply growing the Bi2O2S layer in situ on the surface of monolayer Bi2WO6 nanosheets. The judicious combination of Bi2WO6 and Bi2O2S through a 2D-2D heterojunction not only extended light absorption in the visible range but also significantly enhanced photo(electro)chemical water splitting efficiencies in comparison to the bare Bi2WO6 nanosheets alone due to the close-bonding-promoted interfacial charge separation. Our findings provide a viable methodology to build a host of nanomaterials with closely bonded 2D nanosheets, which can be used as photocatalysts and electrocatalysts, among others.

3.
Nanoscale ; 11(48): 23188-23196, 2019 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-31778138

RESUMO

Dynamic strain based atomic force microscopy (AFM) modes often fail at the interfaces where the most interesting physics occurs because of their incapability of tracking contact resonance accurately under rough topography. To overcome this difficulty, we develop a high-throughput sequential excitation AFM that captures contact dynamics of probe-sample interactions with high fidelity and efficiency, acquiring the spectrum of data on each pixel over a range of frequencies that are excited in a sequential manner. Using electrochemically active granular ceria as an example, we map both linear and quadratic electrochemical strain accurately across grain boundaries with high spatial resolution where the conventional approach fails. The enhanced electrochemical responses point to the accumulation of small polarons in the space charge region at the grain boundaries, thought to be responsible for the enhanced electronic conductivity in nanocrystalline ceria. The spectrum of data can be processed very efficiently by physics-informed principal component analysis (PCA), speeding data processing by several orders of magnitude. This approach can be applied to a variety of AFM modes for studying a wide range of materials and structures on the nanoscale.

4.
ACS Appl Mater Interfaces ; 11(46): 43303-43311, 2019 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-31657211

RESUMO

Along with the rapidly developed power conversion efficiencies (PCEs), operational stability of perovskite solar cells (PSCs) remains a bottleneck for further commercialization. The instability mainly arises from the unstable organic components in the whole devices and the responsive metal electrode to the halogens from perovskites. In this work, we develop a carbide-titanium oxide (C-TiO2) hybrid electron-transporting layer (ETL) and a halogen-resistant Sb electrode on top of the inorganic CsPbI2Br layer to solve the issues of instability. The hybrid C-TiO2 presents a uniform and pinhole-free morphology, adequate band structure and electronic property, and observably strong stability. On the other hand, Sb is demonstrated to be effective to restrict inferior ion diffusion and further perovskite decomposition. As a result, our well-designed PSCs achieve both high efficiencies (14.8% for the champion device) and long-term stabilities (<6% decline @ 85 °C, dark, <10% decline @ 60 °C, continuous illumination) of 1000 h.

5.
Adv Mater ; 31(46): e1903559, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31566819

RESUMO

Large-bandgap perovskites offer a route to improve the efficiency of energy capture in photovoltaics when employed in the front cell of perovskite-silicon tandems. Implementing perovskites as the front cell requires an inverted (p-i-n) architecture; this architecture is particularly effective at harnessing high-energy photons and is compatible with ionic-dopant-free transport layers. Here, a power conversion efficiency of 21.6% is reported, the highest among inverted perovskite solar cells (PSCs). Only by introducing a secondary amine into the perovskite structure to form MA1- x DMAx PbI3 (MA is methylamine and DMA is dimethylamine) are defect density and carrier recombination suppressed to enable record performance. It is also found that the controlled inclusion of DMA increases the hydrophobicity and stability of films in ambient operating conditions: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point, 30 times longer than reported in the best prior inverted PSCs. The unencapsulated devices show record operational stability in ambient air among PSCs.

6.
Adv Sci (Weinh) ; 6(19): 1901000, 2019 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-31592418

RESUMO

Room-temperature magnetoelectric (ME) coupling is developed in artificial multilayers and nanocomposites composed of magnetostrictive and electrostrictive materials. While the coupling mechanisms and strengths in multilayers are widely studied, they are largely unexplored in vertically aligned nanocomposites (VANs), even though theory has predicted that VANs exhibit much larger ME coupling coefficients than multilayer structures. Here, strong transverse and longitudinal ME coupling in epitaxial BaTiO3:CoFe2O4 VANs measured by both optical second harmonic generation and piezoresponse force microscopy under magnetic fields is reported. Phase field simulations have shown that the ME coupling strength strongly depends on the vertical interfacial area which is ultimately controlled by pillar size. The ME coupling in VANs is determined by the competition between the vertical interface coupling effect and the bulk volume conservation effect. The revealed mechanisms shed light on the physical insights of vertical interface coupling in VANs in general, which can be applied to a variety of nanocomposites with different functionalities beyond the studied ME coupling effect.

7.
Science ; 366(6464): 475-479, 2019 10 25.
Artigo em Inglês | MEDLINE | ID: mdl-31649196

RESUMO

Ferroelectrics are usually inflexible oxides that undergo brittle deformation. We synthesized freestanding single-crystalline ferroelectric barium titanate (BaTiO3) membranes with a damage-free lifting-off process. Our BaTiO3 membranes can undergo a ~180° folding during an in situ bending test, demonstrating a super-elasticity and ultraflexibility. We found that the origin of the super-elasticity was from the dynamic evolution of ferroelectric nanodomains. High stresses modulate the energy landscape markedly and allow the dipoles to rotate continuously between the a and c nanodomains. A continuous transition zone is formed to accommodate the variant strain and avoid high mismatch stress that usually causes fracture. The phenomenon should be possible in other ferroelectrics systems through domain engineering. The ultraflexible epitaxial ferroelectric membranes could enable many applications such as flexible sensors, memories, and electronic skins.

8.
Nat Commun ; 10(1): 3951, 2019 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-31477695

RESUMO

Ferroelastic switching in ferroelectric/multiferroic oxides plays a crucial role in determining their dielectric, piezoelectric, and magnetoelectric properties. In thin films of these materials, however, substrate clamping is generally thought to limit the electric-field- or mechanical-force-driven responses to the local scale. Here, we report mechanical-force-induced large-area, non-local, collective ferroelastic domain switching in PbTiO3 epitaxial thin films by tuning the misfit-strain to be near a phase boundary wherein c/a and a1/a2 nanodomains coexist. Phenomenological models suggest that the collective, c-a-c-a ferroelastic switching arises from the small potential barrier between the degenerate domain structures, and the large anisotropy of a and c domains, which collectively generates much larger response and large-area domain propagation. Large-area, non-local response under small stimuli, unlike traditional local response to external field, provides an opportunity of unique response to local stimuli, which has potential for use in high-sensitivity pressure sensors and switches.

9.
Adv Mater ; 31(36): e1902870, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31322309

RESUMO

Triple-cation mixed-halide perovskites of composition Csx (FAy MA1- y )1 -x Pb(Iz Br1 -z )3 (CsFAMA) have been reported to possess excellent photovoltaic efficiency with minimal hysteresis; in this work, nanoscale insight is shed into the roles of illumination-induced polarization and ionic migration in photovoltaic hysteresis. By examining the concurrent evolution of ionic distribution and spontaneous polarization of CsFAMA under light illumination using dynamic-strain-based scanning probe microscopy, strong linear piezoelectricity arising from photoenhanced polarization is observed, while ionic migration is found to be not significantly increased by lightening. Nanoscale photocurrents are mapped under a series of biases using conductive atomic force microscopy, revealing negligible difference between forward and backward scans, and local IV curves reconstructed from principal component analysis show minimal hysteresis of just 1%. These observations at the nanoscale are confirmed in a macroscopic perovskite solar cell made of CsFAMA, exhibiting a high efficiency of 20.11% and with hysteresis index as small as 3%. Ionic migration, polarization, and photocurrent hysteresis are thus directly correlated at the nanoscale, and photoenhanced polarization in triple-cation mixed-halide perovskites is established, which does not contribute to the photovoltaic hysteresis.

10.
Nanotechnology ; 30(33): 335703, 2019 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-30995621

RESUMO

The mechanical properties of two-dimensional (2D) materials are critical for their applications in functional devices as well as for strain engineering. Here, we report the Young's modulus and breaking strength of multilayered InSe, an emerging 2D semiconductor of the layered group III chalcogenide. Few-layer InSe flaks were exfoliated from bulk InSe crystal onto Si/SiO2 substrate with micro-fabricated holes, and indentation tests were carried out using an atomic force microscopy probe. In combination with both continuum analysis and finite element simulation, we measured the Young's modulus of multilayer 2D InSe (>5 L) to be 101.37 ± 17.93 GPa, much higher than its bulk counterpart, while its breaking strength is determined to be 8.68 GPa, approaching the theoretical limit of 10.1 GPa. Density functional theory calculations were also carried out to explain the insensitivity of Young's modulus to the layer count. It is found that 2D InSe is softer than most 2D materials, and exhibits breaking strength higher than that of carbon fiber, yet remaining more compliant, making it ideal for flexible electronics applications. The reliability of our method is also validated by measurement of graphene.

11.
Anal Bioanal Chem ; 411(11): 2405-2414, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30828760

RESUMO

In this paper, a fluorescent method was developed for ochratoxin A (OTA) detection that uses iron-doped porous carbon (MPC) and aptamer-functionalized nitrogen-doped graphene quantum dots (NGQDs-Apt) as probes. In this method, the adsorbance of the NGQDs-Apt on the MPC due to a π-π interaction between the aptamer and the MPC results in the quenching of the fluorescence of the NGQDs-Apt. However, since OTA interacts strongly with the aptamer, the presence of OTA leads to the detachment of the NGQDs-Apt from the MPC, resulting in the resumption of fluorescence from the NGQDs-Apt. When exonuclease I (Exo I) is also added to the solution, this exonuclease specifically digests the aptamer, leading to the release of the OTA back into the solution. This free OTA then interacts with another MPC-NGQDs-Apt system, inducing the release of more NGQDs into the solution, which enhances the fluorescent intensity compared to that of the system with no Exo I. Utilizing this behavior of OTA in the presence of NGQDs-Apt, it was possible to detect concentrations of OTA ranging from 10 to 5000 nM, with a limit of detection of 2.28 nM. Our method was tested by applying it to the detection of OTA in wheat and corn samples. This method has four advantages: (1) the magnetic porous carbon is easy to prepare, its porosity enhances its loading capacity for NGQDs, it highly efficiently quenches the fluorescence of the NGQDs, and its magnetic properties facilitate the separation of the MPC from other species in solution; (2) applying double magnetic separation decreases the background signal; (3) Exo I digests the free aptamer effectively, which allows the resulting free OTA to induce the release of more NGQDs-Apt, ultimately enhancing the fluorescent signal; and (4) the proposed method presented high sensitivity and a wide linear detection range. This method may prove helpful in food safety analysis and new biosensor development (achieved by using different aptamer sequences to that used in the present work). Graphical abstract Exonuclease I (Exo I)-assisted fluorescent method for ochratoxin A (OTA) detection using magnetic porous carbon (MPC), nitrogen-doped graphene quantum dots (NGQDs), and double magnetic separation.


Assuntos
Técnicas Biossensoriais/métodos , Grafite/química , Ferro/química , Nitrogênio/química , Ocratoxinas/análise , Pontos Quânticos/química , Aptâmeros de Nucleotídeos/química , Exodesoxirribonucleases/química , Análise de Alimentos/métodos , Magnetismo/métodos , Porosidade , Espectrometria de Fluorescência/métodos , Triticum/química , Zea mays/química
12.
Adv Mater ; 31(18): e1900826, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30907036

RESUMO

Aluminum (Al) is one of the most attractive anode materials for lithium-ion batteries (LIBs) due to its high theoretical specific capacity, excellent conductivity, abundance, and especially low cost. However, the large volume expansion, originating from the uneven alloying/dealloying reactions in the charge/discharge process, causes structural stress and electrode pulverization, which has long hindered its practical application, especially when assembled with a high-areal-density cathode. Here, an inactive (Cu) and active (Al) co-deposition strategy is reported to homogeneously distribute the alloying sites and disperse the stress of volume expansion, which is beneficial to obtain the structural stability of the Al anode. Owing to the homogeneous reaction and uniform distribution of stress during the charge/discharge process, the assembled full battery (LiFePO4 cathode with a high areal density of ≈7.4 mg cm-2 ) with the Cu-Al@Al anode, achieves a high capacity retention of ≈88% over 200 cycles, suggesting the feasibility of the interfacial design to optimize the structural stability of alloying metal anodes for high-performance LIBs.

13.
Analyst ; 144(5): 1831-1839, 2019 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-30676591

RESUMO

In this paper, a composite material comprised of ZnFe2O4 nanomaterial, carbon nanotubes (CNT) and glucose oxidase (GOD) was synthesized and used for glucose detection. ZnFe2O4-CNT was formed by a one-step solvothermal approach using acid-treated CNT as precursor, then GOD was linked to it by coupling reaction between -NH2 and -COOH. After addition of glucose, which is oxidized by GOD, the intermediate product (H2O2) further oxidizes the 3,3',5,5'-tetramethylbenzidine (TMB) substrate and forms a blue product. This process was accelerated in the presence of peroxidase-mimic ZnFe2O4 nanomaterial and the detected signal intensity was correspondingly enhanced. The linear detection range of glucose was 0.8 to 250 µM, with a limit of detection of 0.58 µM. This may originate from (1) the limited diffusion of intermediate species, which resulted in enhanced local concentrations of reaction compounds; (2) enhanced electron transmission among CNT, GOD and ZnFe2O4; (3) the synergistic enhancement of catalytic activity of ZnFe2O4 compared with other metal oxides; (4) the high loading capacity of ZnFe2O4-CNT for GOD molecules, because of its high surface-to-volume ratio. Meanwhile, this method has reasonable selectivity, stability and reusability and can be used for real serum detection, which may be useful for the development of sensitive biosensors.


Assuntos
Glicemia/análise , Enzimas Imobilizadas/química , Compostos Férricos/química , Glucose Oxidase/química , Nanotubos de Carbono/química , Benzidinas/química , Colorimetria/métodos , Humanos , Peróxido de Hidrogênio/química , Limite de Detecção , Nanocompostos/química
14.
Nanotechnology ; 30(20): 205703, 2019 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-30699396

RESUMO

Collagen is the main protein in extracellular matrix that is found in many connective tissues, and it exhibits piezoelectricity that is expected to correlate with its hierarchical microstructure. Resolving fine electromechanical structure of collagen, however, is challenging, due to its weak piezoresponse, rough topography, and microstructural hierarchy. Here we adopt the newly developed sequential excitation strategy in combination with piezoresponse force microscopy to overcome these difficulties. It excites the local electromechanical response of collagen via a sequence of distinct frequencies, minimizing crosstalk with topography, followed by principal component analysis to remove the background noise and simple harmonic oscillator model for physical analysis and data reconstruction. These enable us to acquire high fidelity mappings of fine electromechanical response at the nanoscale that correlate with the gap and overlap domains of collagen fibrils, which show substantial improvement over conventional piezoresponse force microscopy techniques. It also embodies the spirit of big data atomic force microscopy that can be readily extended into other applications with targeted data acquisition.


Assuntos
Artérias/ultraestrutura , Colágeno/química , Microscopia de Força Atômica/métodos , Animais , Matriz Extracelular/química , Fenômenos Mecânicos , Análise de Componente Principal , Suínos
15.
Nat Commun ; 9(1): 4807, 2018 11 15.
Artigo em Inglês | MEDLINE | ID: mdl-30442950

RESUMO

Organic-inorganic hybrid perovskites are promising candidates for the next-generation solar cells. Many efforts have been made to study their structures in the search for a better mechanistic understanding to guide the materials optimization. Here, we investigate the structure instability of the single-crystalline CH3NH3PbI3 (MAPbI3) film by using transmission electron microscopy. We find that MAPbI3 is very sensitive to the electron beam illumination and rapidly decomposes into the hexagonal PbI2. We propose a decomposition pathway, initiated with the loss of iodine ions, resulting in eventual collapse of perovskite structure and its decomposition into PbI2. These findings impose important question on the interpretation of experimental data based on electron diffraction and highlight the need to circumvent material decomposition in future electron microscopy studies. The structural evolution during decomposition process also sheds light on the structure instability of organic-inorganic hybrid perovskites in solar cell applications.

16.
Sci Rep ; 8(1): 17389, 2018 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-30478382

RESUMO

Ferroelectric functionalized dye-sensitized solar cells were fabricated by using a positively-poled LiNbO3 substrate coated with ITO (ITO-LiNbO3) as a collector electrode and demonstrated enhanced power conversion efficiency. Surface potential properties of TiO2 nanoparticle film coated on the ITO-LiNbO3 (TiO2/ITO-LiNbO3) examined by Kelvin probe force microscopy (KPFM) confirmed that a large electric field (a few 10 V/µm) generated from LiNbO3 can penetrate through the ITO layer and is applied to TiO2 film. This polarization-induced electric field leads to an increased photocurrent density by attracting and promoting electrons to direct transport through the mesoporous TiO2 network toward the collector electrode and a decreased charge recombination by facilitating electrons to pass through fewer boundaries of nanoparticles, resulting in high power conversion efficiency. The power conversion efficiency was enhanced by more than 40% in comparison with that without polarization-induced electric field. Incorporating functional ferroelectrics into photovoltaic cells would be a good strategy in improving photovoltaic performance and is applicable to other types of photovoltaic devices, such as perovskite solar cells.

17.
Nanoscale ; 10(45): 21320-21326, 2018 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-30422134

RESUMO

Artificial intelligence (AI) and machine learning have promised to revolutionize the way we live and work, and one of the particularly promising areas for AI is image analysis. Nevertheless, many current AI applications focus on the post-processing of data, while in both materials sciences and medicine, it is often critical to respond to the data acquired on the fly. Here we demonstrate an artificial intelligence atomic force microscope (AI-AFM) that is capable of not only pattern recognition and feature identification in ferroelectric materials and electrochemical systems, but can also respond to classification via adaptive experimentation with additional probing at critical domain walls and grain boundaries, all in real time on the fly without human interference. Key to our success is a highly efficient machine learning strategy based on a support vector machine (SVM) algorithm capable of high fidelity pixel-by-pixel recognition instead of relying on the data from full mapping, making real time classification and control possible during scanning, with which complex electromechanical couplings at the nanoscale in different material systems can be resolved by AI. For AFM experiments that are often tedious, elusive, and heavily rely on human insight for execution and analysis, this is a major disruption in methodology, and we believe that such a strategy empowered by machine learning is applicable to a wide range of instrumentations and broader physical machineries.

18.
Exp Ther Med ; 16(3): 2763-2769, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30186504

RESUMO

Mast cells (MCs) have been reported to serve a crucial role in allergic diseases, including asthma, allergic rhinitis and anaphylaxis. A previous study revealed that microRNA-126 (miR-126) was associated with airway hyperresponsiveness induced by house dust mites, however the molecular mechanisms were unclear. The present study aimed to investigate the effect of miR-126 on immunoglobulin E (IgE)-regulated MC degranulation and explore its underlying mechanisms. miR-126 expression was quantified using a rat model in vivo and in rat peritoneal mast cells (RPMCs) in vitro. Overexpression or downregulation of miR-126 was established by transfection with miR-126 mimics or miR-126 inhibitors and MC degranulation was subsequently evaluated. The effect of miR-126 on protein kinase B (Akt) and phosphorylated Akt protein expression was examined by western blot analysis. The phosphoinositide 3-kinase (PI3K) inhibitor (LY294002) was used to determine the role of the PI3K/Akt signaling pathway. In addition, cytosolic calcium (Ca2+) levels were measured by a fura-2 assay. The results demonstrated that miR-126 expression was upregulated in the ear tissues of rats with allergic contact dermatitis and IgE-activated MCs. The overexpression of miR-126 in RPMCs was established following miR-126 mimic transfection. The release of ß-hexosaminidase and histamine, markers of MC degranulation, were significantly increased in cells with miR-126 overexpression. The phosphorylation of Akt was significantly increased following transfection with miR-126 mimics in stimulated cells, however the signaling activation was abrogated by LY294002. In addition, Ca2+ influx was significantly promoted in stimulated RPMCs overexpressing miR-126. These results indicate that miR-126 accelerated IgE-mediated MC degranulation associated with the PI3K/Akt signaling pathway by promoting Ca2+ influx. This suggests that miR-126 may be a promising therapeutic target for the treatment of allergic skin diseases.

19.
ACS Nano ; 12(9): 9558-9567, 2018 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-30138564

RESUMO

The ability to electrically write magnetic bits is highly desirable for future magnetic memories and spintronic devices, though fully deterministic, reversible, and nonvolatile switching of magnetic moments by electric field remains elusive despite extensive research. In this work, we develop a concept to electrically switch magnetization via polarization modulated oxygen vacancies, and we demonstrate the idea in a multiferroic epitaxial heterostructure of BaTiO3/Fe3O4 fabricated by pulsed laser deposition. The piezoelectricity and ferroelectricity of BaTiO3 have been confirmed by macro- and microscale measurements, for which Fe3O4 serves as the top electrode for switching the polarization. X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra indicate a mixture of Fe2+ and Fe3+ at O h sites and Fe3+ at T d sites in Fe3O4, while the room-temperature magnetic domains of Fe3O4 are revealed by microscopic magnetic force microscopy measurements. It is demonstrated that the magnetic domains of Fe3O4 can be switched by not only magnetic fields but also electric fields in a deterministic, reversible, and nonvolatile manner, wherein polarization reversal by electric field modulates the oxygen vacancy distribution in Fe3O4, and thus its magnetic state, making it attractive for electrically written magnetic memories.

20.
Langmuir ; 34(33): 9847-9855, 2018 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-30044634

RESUMO

The orientation and conformation of adhesive proteins after adsorption play a central role in cell-binding bioactivity. Fibronectin (Fn) holds two peptide sequences that favor cell adhesion: the Arg-Gly-Asp (RGD) loop on the tenth type-III domain (Fn-III10) and the Pro-His-Ser-Arg-Asn (PHSRN) synergy site on the ninth type-III domain (Fn-III9). Herein, adsorption of Fn fragments (Fn-III10 and Fn-III9-10) on self-assembled monolayers (SAMs) carrying various functional groups (-COOH, -NH2, -CH3, and -OH) was investigated by the Monte Carlo method and molecular dynamics simulation in order to understand its mediation effect on cell adhesion. The results demonstrated that Fn-III9 could enhance the stiffness of the Fn molecule and further fix the adsorption orientation. The RGD site of the Fn fragment appeared to be deactivated on hydrophobic surfaces (CH3-SAM) because of the binding of adjacent nonpolar residues on surfaces, whereas charged surfaces (COOH-SAM and NH2-SAM) and hydrophilic surfaces (OH-SAM) were conducive to the formation of cell-binding-favorable orientation for Fn fragments. The cell adhesion capability of Fn fragments was highly improved on positively charged surfaces (NH2-SAM) and hydrophilic surfaces because of the advantageous steric structure and orientation of both RGD and PHSRN sites. This work provides an insight into the interplay at the atomic scale between protein adsorption and surface chemistry for designing biologically responsive substrate surfaces.


Assuntos
Fibronectinas/química , Adsorção , Adesão Celular , Domínio de Fibronectina Tipo III , Simulação de Dinâmica Molecular , Método de Monte Carlo , Eletricidade Estática
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