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 WSe₂ 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 (MoS₂) and tungsten diselenides (WSe₂), 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 WSe₂ 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 WSe₂ along the step edges on the sapphire substrate. In addition, such atomic steps facilitate a layer-over-layer overlapping process to form few-layer WSe₂ 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 WSe₂ and adds fresh knowledge on the growth mechanism of WSe₂ 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 WSe₂ by Sulfur-Assisted Chemical Vapor Deposition

Two-dimensional (2D) layered tungsten diselenides (WSe₂) 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 WSe₂ is not as straightforward as other 2D materials due to the low reactivity between reactants in WSe₂ synthesis. In addition, the growth mechanism of WSe₂ in such CVD process remains unclear. Here we report the observation of a screw-dislocation-driven (SDD) spiral growth of 2D WSe₂ flakes and pyramid-like structures using a sulfur-assisted CVD method. Few-layer and pyramid-like WSe₂ flakes instead of monolayer were synthesized by introducing a small amount of sulfur as a reducer to help the selenization of WO₃, 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 WSe₂. The generation and propagation mechanisms of screw dislocations during the growth of WSe₂ were discussed. Back-gated field-effect transistors were made on these 2D WSe₂ materials, which show on/off current ratios of 10⁶ and mobility up to 44 cm²/(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 (NO₂) using field-effect transistors based on multilayer black phosphorus. Black phosphorus sensors exhibited increased conduction upon NO₂ exposure and excellent sensitivity for detection of NO₂ down to 5 ppb. Moreover, when the multilayer black phosphorus field-effect transistor was exposed to NO₂ 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 NO₂ on black phosphorus were extracted for different NO₂ 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, LiCoO₂ and LiNi_0.5Mn_1.5O₄ cathodes were used to pair up with the HCC-M-Si anode to fabricate full cells. With LiNi_0.5Mn_1.5O₄ 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_0.5Mn_1.5O₄ cathode delivers 46% more energy density than that of the full cell with a LiCoO₂ 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_20.56(1)Sb_0.44(1), 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_20.56(1)Sb_0.44(1) 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 cm²/V·s), a reasonably high on/off current ratio (∼10³), and intrinsic responsivity up to 10 μA/W. Our results demonstrate the potential of P_20.56(1)Sb_0.44(1) thin flakes as a two-dimensional material for applications in visible light detectors