89 research outputs found
Temperature and pH Dual-Responsive Core-Brush Nanocomposite for Enrichment of Glycoproteins
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 CuÂ(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
Boronic Acid Terminated Thermo-Responsive and Fluorogenic Polymer: Controlling Polymer Architecture for Chemical Sensing and Affinity Separation
Thermo-responsive polyÂ(<i>N</i>-isopropylacrylamide)
(polyNIPAm) containing terminal boronic acid was synthesized using
atom transfer radical polymerization (ATRP) in combination with CuÂ(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)Âphenylboronic
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
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
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
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
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
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 CuÂ(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
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
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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