82 research outputs found

    Temperature and pH Dual-Responsive Core-Brush Nanocomposite for Enrichment of Glycoproteins

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    In this report, we present a novel modular approach to the immobilization of a high density of boronic acid ligands on thermoresponsive block copolymer brushes for effective enrichment of glycoproteins via their synergistic multiple covalent binding with the immobilized boronic acids. Specifically, a two-step, consecutive surface-initiated atom transfer radical polymerization (SI-ATRP) was employed to graft a flexible block copolymer brush, pNIPAm-<i>b</i>-pGMA, from an initiator-functionalized nanosilica surface, followed by postpolymerization modification of the pGMA moiety with sodium azide. Subsequently, an alkyne-tagged boronic acid (PCAPBA) was conjugated to the polymer brush via a Cu­(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction, leading to a silica-supported polymeric hybrid material, Si@pNIPAm-<i>b</i>-pBA, with a potent glycol binding affinity. The obtained core-brush nanocomposite was systematically characterized with regard to particle size, morphology, organic content, brush density, and number of immobilized boronic acids. We also studied the characteristics of glycoprotein binding of the nanocomposite under different conditions. The nanocomposite showed high binding capacities for ovalbumin (OVA) (98.0 mg g<sup>–1</sup>) and horseradish peroxidase (HRP) (26.8 mg g<sup>–1</sup>) in a basic buffer (pH 9.0) at 20 °C. More importantly, by adjusting the pH and temperature, the binding capacities of the nanocomposite can be tuned, which is meaningful for the separation of biological molecules. In general, the synthetic approach developed for the fabrication of block copolymer brushes in the nanocomposite opened new opportunities for the design of more functional hybrid materials that will be useful in bioseparation and biomedical applications

    High-Performance Broadband Floating-Base Bipolar Phototransistor Based on WSe<sub>2</sub>/BP/MoS<sub>2</sub> Heterostructure

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    Recently, there are increasing interests in two-dimensional materials, as a result of their outstanding electrical and optical properties and numerous potential applications in optoelectronic devices. Here, we first report on a bipolar phototransistor based on WSe<sub>2</sub>-BP-MoS<sub>2</sub> van der Waals heterostructure, showing its broadband photoresponse from visible to the infrared spectral regions. Broadband photoresponsivities for visible (532 nm) and the infrared (1550 nm) light waves reach up to 6.32 and 1.12 A W<sup>1–</sup>, respectively, which are both improved by tens of times in comparison with similar photodiode devices composed of WSe<sub>2</sub>-BP. The phototransistor also exhibits ultrasensitive shot noise limit specific detectivities which are 1.25 × 10<sup>11</sup> Jones for visible light at wavelength λ = 532 nm and 2.21 × 10<sup>10</sup> Jones for the near-infrared light at wavelength λ = 1550 nm at room temperature. It is a promising candidate for progressive development of photodetector, with implementation of smaller sensor elements, large sensing area, super-high integration, and broadband photoresponse

    Boronic Acid Terminated Thermo-Responsive and Fluorogenic Polymer: Controlling Polymer Architecture for Chemical Sensing and Affinity Separation

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    Thermo-responsive poly­(<i>N</i>-isopropylacrylamide) (polyNIPAm) containing terminal boronic acid was synthesized using atom transfer radical polymerization (ATRP) in combination with Cu­(I)-catalyzed alkyne–azide 1,3-dipolar cycloaddition (CuAAC) reaction. Alkyne-terminated polyNIPAm was first synthesized by ATRP using an alkyne-containing initiator. A fluorogenic boronic acid, 3-(2-azido-acetylamino)­phenylboronic acid (APBA) was then linked to the polyNIPAm through CuAAC. The synthesized polymers were characterized by <sup>1</sup>H NMR, FT-IR, UV–vis, matrix-assisted laser desorption/ionization time-of-flight (MALDI–TOF) mass spectrometry, and turbidity measurements. The intensity of fluorescence emission of the boronic acid-terminated polyNIPAm (BA-polyNIPAm) was found to increase when increasing amount of a cis-diol compound (i.e., fructose) was added. At physiological pH value, the BA-polyNIPAm effectively bound fructose and could be easily separated from aqueous solution by raising the temperature above its lower critical solution temperature (LCST)

    Deterministic fibre tracking improved by diffusion tensor similarity

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    Fibre tracking is a non-invasive technique based on Diffusion Tensor Imaging (DTI) that provides useful information about biological anatomy and connectivity. In this paper, we propose a new tractography algorithm, named TAS (Tracking by Angle and Similarity), which is able to overcome the shortfalls of existing algorithms by considering not only the main diffusion directions, but also the similarity of diffusion tensors. The algorithm achieved better tracking results in simulation experiments. Fibre tracking from a real brain dataset is presented

    Near-Infrared Photodetector Based on MoS<sub>2</sub>/Black Phosphorus Heterojunction

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    Two-dimensional (2D) materials present their excellent properties in electronic and optoelectronic applications, including in ultrafast carrier dynamics, layer-dependent energy bandgap, tunable optical properties, low power dissipation, high mobility, transparency, flexibility, and the ability to confine electromagnetic energy to extremely small volumes. Herein, we demonstrate a photodetector with visible to near-infrared detection range, based on the heterojunction fabricated by van der Waals assembly between few-layer black phosphorus (BP) and few-layer molybdenum disulfide (MoS<sub>2</sub>). The heterojunction with electrical characteristics which can be electrically tuned by a gate voltage achieves a wide range of current-rectifying behavior with a forward-to-reverse bias current ratio exceeding 10<sup>3</sup>. The photoresponsivity (<i>R</i>) of the photodetector is about 22.3 A W<sup>–1</sup> measured at λ = 532 nm and 153.4 mA W<sup>–1</sup> at λ = 1.55 μm with a microsecond response speed (15 μs). In addition, its specific detectivity <i>D</i>* is calculated to have the maximum values of 3.1 × 10<sup>11</sup> Jones at λ = 532 nm, while 2.13 × 10<sup>9</sup> Jones at λ = 1550 nm at room temperature

    Fabrication of Large-Sized Two-Dimensional Ordered Surface Array with Well-Controlled Structure via Colloidal Particle Lithography

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    Epoxy resin coated glass slides were used for colloidal particle lithography, in order to prepare well-defined 2D surface arrays. Upon the assistance of a large-sized 2D colloidal single crystal as template, centimeter-sized ordered surface arrays of bowl-like units were obtained. Systematic studies revealed that the parameters of obtained surface arrays could be readily controlled by some operational factors, such as temperature, epoxy resin layer thickness, and template particle size. With epoxy resin substituting for normal linear polymer, the height/diameter ratio of bowls in the formed surface arrays can be largely increased. With further reactive plasma etching, the parameters of ordered surface arrays could be finely tuned through controlling etching time. This study provides a facile way to prepare large-sized 2D surface arrays with tunable parameters

    In Situ Preparation of Mo<sub>2</sub>C Nanoparticles Embedded in Ketjenblack Carbon as Highly Efficient Electrocatalysts for Hydrogen Evolution

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    Recently, to enhance the catalytic activity of molybdenum carbide (Mo<sub>2</sub>C) electrocatalysts for the hydrogen evolution reaction (HER), the conductive carbon-based materials with different structures have been used to support Mo<sub>2</sub>C particles for providing sufficient catalytic hydrogen production sites. Nevertheless, it is always hard to use a simple method to ensure both uniform distribution of Mo<sub>2</sub>C particles and good charge transfer between Mo<sub>2</sub>C and carbon matrix. Herein, we used a low-cost carbonaceous material as ingredient via a facile method of in situ carbonization to design the structure of Mo<sub>2</sub>C nanoparticles embedded in chainlike Ketjenblack carbon (KB) with strong chemical link, to achieve the Mo<sub>2</sub>C/KB hybrid catalyst with uniform distribution of active Mo<sub>2</sub>C nanocrystals on KB for high density of catalytic sites and excellent charge-transfer ability. Moreover, the effects of carbonization temperature and carbon content on the HER activity were investigated to optimize the Mo<sub>2</sub>C/KB catalyst. The optimized Mo<sub>2</sub>C/KB catalyst exhibits outstanding HER activity in both acidic and alkaline media with small Tafel slopes of 49 and 48 mV dec<sup>–1</sup>, low overpotentials, and remarkable stability. The enhanced HER activity of Mo<sub>2</sub>C/KB catalyst could be ascribed to its unique chainlike structure with a large specific surface area of 580.3 m<sup>2</sup> g<sup>–1</sup>, the high electronic conductivity, and active Mo<sub>2</sub>C nanocrystals protected by robust carbon matrix

    Fluorescent Boronic Acid Polymer Grafted on Silica Particles for Affinity Separation of Saccharides

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    Boronic acid affinity gels are important for effective separation of biological active cis-diols, and are finding applications both in biotech industry and in biomedical research areas. To increase the efficacy of boronate affinity separation, it is interesting to introduce repeating boronic acid units in flexible polymer chains attached on solid materials. In this work, we synthesize polymer brushes containing boronic acid repeating units on silica gels using surface-initiated atom transfer radical polymerization (ATRP). A fluorescent boronic acid monomer is first prepared from an azide-tagged fluorogenic boronic acid and an alkyne-containing acrylate by Cu­(I)-catalyzed 1,3-dipolar cycloaddition reaction (the CuAAC click chemistry). The boronic acid monomer is then grafted to the surface of silica gel modified with an ATRP initiator. The obtained composite material contains boronic acid polymer brushes on surface and shows favorable saccharide binding capability under physiological pH conditions, and displays interesting fluorescence intensity change upon binding fructose and glucose. In addition to saccharide binding, the flexible polymer brushes on silica also enable fast separation of a model glycoprotein based on selective boronate affinity interaction. The synthetic approach and the composite functional material developed in this work should open new opportunities for high efficiency detection, separation, and analysis of not only simple saccharides, but also glycopeptides and large glycoproteins

    Precise Engineering of Conductive Pathway by Frictional Direct-Writing for Ultrasensitive Flexible Strain Sensors

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    Highly sensitive strain sensors that can detect small strain are in high demand in the fields of displays, robotics, fatigue detection, body monitoring, in vitro diagnostics, and advanced therapies. However, resistive-type sensors that are composed of electrically conductive sensing films coupled with flexible substrates suffer from the limits that their gauge factors (GFs) at small strains (e.g., 0.1–1%) are not high. Herein, through frictional direct-writing of graphite rod on the composite paper substrates, we produced strain sensors with extremely high gauge factor at small strains. The sensors exhibited a gauge factor of 9720 at a small strain of 0.9%, minimum strain detection up to 0.05%, strain resolution of 0.05%, response time of 40 ms, and high stability (>5000 bending–unbending cycles). Compared with the literature results so far, our sensors hold the highest GF value at small strains. Such high sensitivities are due to the precise control of narrow two-dimensional percolative conductive pathway, which means the content of conductive graphite sheets is close to the conductive percolation threshold. The strain sensors have a rapid response to microdeformation changes and can monitor various structural changes, including human motion, through facilitative and effective installation of device designs

    Facile Preparation of Superelastic and Ultralow Dielectric Boron Nitride Nanosheet Aerogels via Freeze-Casting Process

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    As a structural analogue of graphene, boron nitride nanosheets (BNNSs) have attracted ever-growing research interest in the past few years, due to their remarkably mechanical, electrical, and thermal properties. The preparation of BNNS aerogels is considered to be one of the most effective approaches for their practical applications. However, it has remained a great challenge to fabricate BNNS aerogels with superelasticity by a facile method. Here, we report the preparation of BNNS aerogels via a facile method involving polymer-assisted cross-linking and freeze-casting strategies. The resulting aerogels exhibit a well-ordered and anisotropic microstructure, leading to anisotropic superelasticity, high compressive strength, and excellent energy absorption ability. The unique microstructure also endows the aerogels with ultralow dielectric constant (1.24) and loss (∼0.003). The successful fabrication of such fascinating materials paves the way for application of BNNSs in energy-absorbing services, catalyst carrier, and environmental remediation, etc
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