15 research outputs found
Preservation of Supported Lipid Membrane Integrity from Thermal Disruption: Osmotic Effect
Preservation
of structural integrity under various environmental conditions is
one major concern in the development of the supported lipid membrane
(SLM)-based devices. It is common for SLMs to experience temperature
shifts from manufacture, processing, storage, and transport to operation.
In this work, we studied the thermal adaption of the supported membranes
on silica substrates. Homogenous SLMs with little defects were formed
through the vesicle fusion method. The mass and fluidity of the bilayers
were found to deteriorate from a heating process but not a cooling
process. Fluorescence characterizations showed that the membranes
initially budded as a result of heating-induced lipid lateral area
expansion, followed by the possible fates including maintenance, retraction,
and fission, among which the last contributes to the irreversible
compromise of the SLM integrity and spontaneous release of the interlipid
stress accumulated. Based on the mechanism, we developed a strategy
to protect SLMs from thermal disruption by increasing the solute concentration
in medium. An improved preservation of the membrane mass and fluidity
against the heating process was observed, accompanied by a decrease
in the retraction and fission of the buds. Theoretical analysis revealed
a high osmotic energy penalty for the fission, which accounts for
the depressed disruption. This osmotic-based protection strategy is
facile, solute nonspecific, and long-term efficient and has little
impact on the original SLM properties. The results may help broaden
SLM applications and sustain the robustness of SLM-based devices under
multiple thermal conditions
Molecular Response and Cooperative Behavior during the Interactions of Melittin with a Membrane: Dissipative Quartz Crystal Microbalance Experiments and Simulations
The molecular-level interactions of an antimicrobial
peptide melittin with supported membrane were studied by the combination
of dissipative quartz crystal microbalance (QCM-D) experiments and
computer simulations. We found the response behavior of lipids upon
peptide adsorption greatly influence their interactions. The perturbance
and reorientation of the lipid in liquid phase facilitate the insertion
of melittin in a trans-membrane way, but in solid phase, asymmetrical
membrane disruption happens. Apart from the lipid state, the local
peptide-to-lipid ratio also affects the insertion capacity of melittin.
When the local peptide number density is high, adjacent peptides can
cooperatively penetrate into the membrane. This observation explains
the occurrence of the conventional “carpet” mechanism
Effect of Osmotic Stress on Membrane Fusion on Solid Substrate
There is currently
a lack of comprehensive understanding of osmotic
effect on lipid vesicle fusion on solid oxide surface. The question
has both biological and biomedical implications. We studied the effect
by quartz crystal microbalance with dissipation monitoring using NaCl,
sucrose as osmolytes, and two different osmotic stress imposition
methods, which allowed us to separate the osmotic effects from the
solute impacts. Osmotic stress was found to have limited influence
on the fusion kinetics, independently of the direction of the gradient.
Further atomic force microscopy experiments and energy consideration
implied that osmotic stress spends the majority of chemical potential
energy associated in directed transport of water across membrane.
Its contribution to vesicle deformation and fusion on substrate is
therefore small compared to that of adhesion
Controlled Drug Loading and Release of a Stimuli-Responsive Lipogel Consisting of Poly(<i>N</i>‑isopropylacrylamide) Particles and Lipids
Environmentally responsive materials
are attractive for advance
biomedicine applications such as controlled drug delivery and gene
therapies. Recently, we have introduced the fabrication of a novel
type of stimuli-sensitive lipogel composite consisting of poly(<i>N</i>-isopropylacrylamide) (pNIPAM) microgel particles and lipids.
In this study, we demonstrated the temperature-triggered drug release
behavior and the tunable drug loading and release capacities of the
lipogel. At room temperature (22 °C), no calcein was released
from the lipogel over time. At body temperature (37 °C), the
release process was significantly promoted; lipids in the lipogel
acted as drug holders on the pNIPAM scaffold carrier and prolonged
the calcein release process from 10 min to 2 h. Furthermore, the loading
and release of calcein could be effectively controlled by modulating
the relative amount of lipids incorporated in the lipogel, which can
be realized by the salt-induced lipid release of the lipogel
Step-Edge-Guided Nucleation and Growth of Aligned WSe<sub>2</sub> on Sapphire <i>via</i> a Layer-over-Layer Growth Mode
Two-dimensional (2D) materials beyond graphene have drawn a lot of attention recently. Among the large family of 2D materials, transitional metal dichalcogenides (TMDCs), for example, molybdenum disulfides (MoS<sub>2</sub>) and tungsten diselenides (WSe<sub>2</sub>), have been demonstrated to be good candidates for advanced electronics, optoelectronics, and other applications. Growth of large single-crystalline domains and continuous films of monolayer TMDCs has been achieved recently. Usually, these TMDC flakes nucleate randomly on substrates, and their orientation cannot be controlled. Nucleation control and orientation control are important steps in 2D material growth, because randomly nucleated and orientated flakes will form grain boundaries when adjacent flakes merge together, and the formation of grain boundaries may degrade mechanical and electrical properties of as-grown materials. The use of single crystalline substrates enables the alignment of as-grown TMDC flakes via a substrate–flake epitaxial interaction, as demonstrated recently. Here we report a step-edge-guided nucleation and growth approach for the aligned growth of 2D WSe<sub>2</sub> by a chemical vapor deposition method using C-plane sapphire as substrates. We found that at temperatures above 950 °C the growth is strongly guided by the atomic steps on the sapphire surface, which leads to the aligned growth of WSe<sub>2</sub> along the step edges on the sapphire substrate. In addition, such atomic steps facilitate a layer-over-layer overlapping process to form few-layer WSe<sub>2</sub> structures, which is different from the classical layer-by-layer mode for thin-film growth. This work introduces an efficient way to achieve oriented growth of 2D WSe<sub>2</sub> and adds fresh knowledge on the growth mechanism of WSe<sub>2</sub> and potentially other 2D materials
Influence of Surface Chemistry on Particle Internalization into Giant Unilamellar Vesicles
Cellular uptake of materials plays
a key role in their biomedical
applications. In this work, based on the cell-mimic giant unilamellar
vesicles (GUVs) and a novel type of microscale materials consisting
of stimuli-responsive poly(<i>N</i>-isopropylacrylamide)
microgel particles and the incorporated lipids, the influence of particle
surface chemistry, including hydrophobic/hydrophilic property and
lipid decorations, on the adsorption and consequent internalization
of particles into GUVs was investigated. It is found that the decoration
of particle surface with lipids facilitates the adsorption of particles
on GUV membrane. After that, the hydrophobic property of particle
surface further triggers the internalization of particles into GUVs.
These results demonstrate the importance of surface properties of
particles on their interactions with lipid membranes and are helpful
to the understanding of cellular uptake mechanism
Screw-Dislocation-Driven Growth of Two-Dimensional Few-Layer and Pyramid-like WSe<sub>2</sub> by Sulfur-Assisted Chemical Vapor Deposition
Two-dimensional (2D) layered tungsten diselenides (WSe<sub>2</sub>) material has recently drawn a lot of attention due to its unique optoelectronic properties and ambipolar transport behavior. However, direct chemical vapor deposition (CVD) synthesis of 2D WSe<sub>2</sub> is not as straightforward as other 2D materials due to the low reactivity between reactants in WSe<sub>2</sub> synthesis. In addition, the growth mechanism of WSe<sub>2</sub> in such CVD process remains unclear. Here we report the observation of a screw-dislocation-driven (SDD) spiral growth of 2D WSe<sub>2</sub> flakes and pyramid-like structures using a sulfur-assisted CVD method. Few-layer and pyramid-like WSe<sub>2</sub> flakes instead of monolayer were synthesized by introducing a small amount of sulfur as a reducer to help the selenization of WO<sub>3</sub>, which is the precursor of tungsten. Clear observations of steps, helical fringes, and herringbone contours under atomic force microscope characterization reveal the existence of screw dislocations in the as-grown WSe<sub>2</sub>. The generation and propagation mechanisms of screw dislocations during the growth of WSe<sub>2</sub> were discussed. Back-gated field-effect transistors were made on these 2D WSe<sub>2</sub> materials, which show on/off current ratios of 10<sup>6</sup> and mobility up to 44 cm<sup>2</sup>/(V·s)
Black Phosphorus Gas Sensors
The utilization of black phosphorus and its monolayer (phosphorene) and few-layers in field-effect transistors has attracted a lot of attention to this elemental two-dimensional material. Various studies on optimization of black phosphorus field-effect transistors, PN junctions, photodetectors, and other applications have been demonstrated. Although chemical sensing based on black phosphorus devices was theoretically predicted, there is still no experimental verification of such an important study of this material. In this article, we report on chemical sensing of nitrogen dioxide (NO<sub>2</sub>) using field-effect transistors based on multilayer black phosphorus. Black phosphorus sensors exhibited increased conduction upon NO<sub>2</sub> exposure and excellent sensitivity for detection of NO<sub>2</sub> down to 5 ppb. Moreover, when the multilayer black phosphorus field-effect transistor was exposed to NO<sub>2</sub> concentrations of 5, 10, 20, and 40 ppb, its relative conduction change followed the Langmuir isotherm for molecules adsorbed on a surface. Additionally, on the basis of an exponential conductance change, the rate constants for adsorption and desorption of NO<sub>2</sub> on black phosphorus were extracted for different NO<sub>2</sub> concentrations, and they were in the range of 130–840 s. These results shed light on important electronic and sensing characteristics of black phosphorus, which can be utilized in future studies and applications
Hierarchical Carbon-Coated Ball-Milled Silicon: Synthesis and Applications in Free-Standing Electrodes and High-Voltage Full Lithium-Ion Batteries
Lithium-ion batteries
have been regarded as one of the most promising
energy storage devices, and development of low-cost batteries with
high energy density is highly desired so that the cost per watt-hour
($/Wh) can be minimized. In this work, we report using ball-milled
low-cost silicon (Si) as the starting material and subsequent carbon
coating to produce low-cost hierarchical carbon-coated (HCC) Si. The
obtained particles prepared from different Si sources all show excellent
cycling performance of over 1000 mAh/g after 1000 cycles. Interestingly,
we observed <i>in situ</i> formation of porous Si, and it
is well confined in the carbon shell based on postcycling characterization
of the hierarchical carbon-coated metallurgical Si (HCC-M-Si) particles.
In addition, lightweight and free-standing electrodes consisting of
the HCC-M-Si particles and carbon nanofibers were fabricated, which
achieved 1015 mAh/g after 100 cycles based on the total mass of the
electrodes. Compared with conventional electrodes, the lightweight
and free-standing electrodes significantly improve the energy density
by 745%. Furthermore, LiCoO<sub>2</sub> and LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> cathodes were used to pair up with the HCC-M-Si
anode to fabricate full cells. With LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> as cathode, an energy density up to 547 Wh/kg was achieved
by the high-voltage full cell. After 100 cycles, the full cell with
a LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4</sub> cathode delivers
46% more energy density than that of the full cell with a LiCoO<sub>2</sub> cathode. The systematic investigation on low-cost Si anodes
together with their applications in lightweight free-standing electrodes
and high-voltage full cells will shed light on the development of
high-energy Si-based lithium-ion batteries for real applications
Synthesis, Characterization, and Device Application of Antimony-Substituted Violet Phosphorus: A Layered Material
Two-dimensional
(2D) nanoflakes have emerged as a class of materials
that may impact electronic technologies in the near future. A challenging
but rewarding work is to experimentally identify 2D materials and
explore their properties. Here, we report the synthesis of a layered
material, P<sub>20.56(1)</sub>Sb<sub>0.44(1)</sub>, with a systematic
study on characterizations and device applications. This material
demonstrates a direct band gap of around 1.67 eV. Using a laser-cutting
method, the thin flakes of this material can be separated into multiple
segments. We have also fabricated field effect transistors based on
few-layer P<sub>20.56(1)</sub>Sb<sub>0.44(1)</sub> flakes with a thickness
down to a few nanometers. Interestingly, these field effect transistors
show strong photoresponse within the wavelength range of visible light.
At room temperature, we have achieved good mobility values (up to
58.96 cm<sup>2</sup>/V·s), a reasonably high on/off current ratio
(∼10<sup>3</sup>), and intrinsic responsivity up to 10 μA/W.
Our results demonstrate the potential of P<sub>20.56(1)</sub>Sb<sub>0.44(1)</sub> thin flakes as a two-dimensional material for applications
in visible light detectors