Focal adhesions play an important role in cell spreading,migration,and overall mechanical integrity.The relationship of cell structural and mechanical properties was investigated in the context of focal adhesion proce...Focal adhesions play an important role in cell spreading,migration,and overall mechanical integrity.The relationship of cell structural and mechanical properties was investigated in the context of focal adhesion processes.Combined atomic force microscopy(AFM) and laser scanning confocal microscopy(LSCM) was utilized to measure single cell mechanics,in correlation with cellular morphology and membrane structures at a nanometer scale.Characteristic stages of focal adhesion were verified via confocal fluorescent studies,which confirmed three representative F-actin assemblies,actin dot,filaments network,and long and aligned fibrous bundles at cytoskeleton.Force-deformation profiles of living cells were measured at the single cell level,and displayed as a function of height deformation,relative height deformation and relative volume deformation.As focal adhesion progresses,single cell compression profiles indicate that both membrane and cytoskeleton stiffen,while spreading increases especially from focal complex to focal adhesion.Correspondingly,AFM imaging reveals morphological geometries of spherical cap,spreading with polygon boundaries,and elongated or polarized spreading.Membrane features are dominated by protrusions of 41-207 nm tall,short rods with 1-6 μm in length and 10.2-80.0 nm in height,and long fibrous features of 31-246 nm tall,respectively.The protrusion is attributed to local membrane folding,and the rod and fibrous features are consistent with bilayer decorating over the F-actin assemblies.Taken collectively,the reassembly of F-actin during focal adhesion formation is most likely responsible for the changes in cellular mechanics,spreading morphology,and membrane structural features.展开更多
By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrop...By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.展开更多
Direct observation is arguably the preferred way to investigate the interactions between two molecular complexes. With the development of high speed atomic force microscopy （AFM）, it is becoming possible to observe ...Direct observation is arguably the preferred way to investigate the interactions between two molecular complexes. With the development of high speed atomic force microscopy （AFM）, it is becoming possible to observe directly DNA-protein interactions with relevant spatial and temporal resolutions. These interactions are of central importance to biology, bionanotechnology, and functional biologically inspired materials. As in all microscopy studies, sample preparation plays a central role in AFM observation and minimal perturbation of the sample is desired. Here, we demonstrate the ability to tune the interactions between DNA molecules and the surface to create an association strong enough to enable high-resolution AFM imaging while also providing sufficient translational freedom to allow the relevant protein-DNA interactions to take place. Furthermore, we describe a quantitative method for measuring DNA mobility, while also determining the individual forces contributing to DNA movement. We found that for a weak surface association, a significant contribution to the movement arises from the interaction of the AFM tip with the DNA. In combination, these methods enable the tuning of the surface translational freedom of DNA molecules to allow the direct study of a wide range of nucleo-protein interactions by high speed atomic force microscopy.展开更多
In this article, a detailed analysis of the wet- etching technique for AIGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxida...In this article, a detailed analysis of the wet- etching technique for AIGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxida- tion plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation tem- perature and time. The correlation of etching roughness with oxidation time and temperature was investigated. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for A1GaN layer was given.展开更多
We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room ...We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room temperature gas sensor. The device was carefully designed and fabricated using standard integrated processing to achieve the 16 nm EFN that can be used for sensing without any need for surface modification. The effective diameter for the EFN was determined using Kelvin probe force microscopy accompanied by three- dimensional electrostatic simulations. We show that the EFN transistor is capable of detecting 100 parts per million of ethanol gas with bare SiO2.展开更多
Studying interaction between peptides and lipid membranes is helpful for understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides, which are toxic to cells through disruption of the cel...Studying interaction between peptides and lipid membranes is helpful for understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides, which are toxic to cells through disruption of the cell membrane. Although many efforts have been made to find out common mechanisms of the peptide-induced membrane disruption, detailed information on how the peptide's amino acid sequence affects its interaction with lipid bilayers is still lacking. In this study, three peptides termed as Pep11, P11-2, and QQ11, which share a similar backbone, were employed to explore how modifications on the peptide sequence as well as terminal groups influenced its interaction with the lipid membrane. Atomic force microscopy data revealed that the peptides could deposit on the membranes and induce defects with varied morphologies and stiffness. Fluorescence resonance energy transfer(FRET) experiments indicated that the introduction of the three peptides resulted in different FRET effects on either liquid or gel lipid membranes. DPH fluorescence anisotropy and Laurdan's generalized polarization analysis showed that P11-2 could insert into the lipid membrane and impact the lipid hydrophobic region while QQ11 influenced the order of the hydrophilic head of the lipid membrane. With these results, we have illustrated how these peptides interacted differently with the lipid membrane because of the modification of their sequences. Although these peptides did not relate to disease and antibiosis, we hope these results still could provide some clues for partly understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides.展开更多
Control of blend morphology at multi-scale is critical for optimizing the power conversion efficiency(PCE)of plastic solar cells.To better understand the physics of photoactive layer in the organic photovoltaic device...Control of blend morphology at multi-scale is critical for optimizing the power conversion efficiency(PCE)of plastic solar cells.To better understand the physics of photoactive layer in the organic photovoltaic devices,it is necessary to gain understanding of morphology and the corresponding electronic property.Herein we report the correlation between nanoscale structural,electric properties of bulk heterojunction(BHJ)solar cells and the annealing-induced PCE change.We demonstrate that the PCE of BHJ solar cells are dramatically improved(from1.3%to 4.6%)by thermal annealing,which results from P3HT crystalline stacking and the PCBM aggregation for interpenetrated network.The similar trend for annealinginduced photovoltage and PCE evolution present as an initial increase followed by a decrease with the annealing time and temperature.The surface roughness increase slowly and then abruptly after the same inflection points observed for photovoltage and PCE.The phase images in electric force microscopy indicate the optimized P3HT and PCBM crystallization for interpenetrating network formation considering the spectroscopic results as well.From the correlation between surface photovoltage,blend morphology,and PCE,we propose a model to illustrate the film structure and its evolution under different annealing conditions.This work would benefit the better design and optimization of the morphology and local electric properties of solar cell active layers for improved PCE.展开更多
基金initiated by a UCD Alzheimer's Disease Center (ADC) pilotgranta CRCC (Cancer Research Coordination Committee) Research Grantthe support of W. M. Keck Foundation
文摘Focal adhesions play an important role in cell spreading,migration,and overall mechanical integrity.The relationship of cell structural and mechanical properties was investigated in the context of focal adhesion processes.Combined atomic force microscopy(AFM) and laser scanning confocal microscopy(LSCM) was utilized to measure single cell mechanics,in correlation with cellular morphology and membrane structures at a nanometer scale.Characteristic stages of focal adhesion were verified via confocal fluorescent studies,which confirmed three representative F-actin assemblies,actin dot,filaments network,and long and aligned fibrous bundles at cytoskeleton.Force-deformation profiles of living cells were measured at the single cell level,and displayed as a function of height deformation,relative height deformation and relative volume deformation.As focal adhesion progresses,single cell compression profiles indicate that both membrane and cytoskeleton stiffen,while spreading increases especially from focal complex to focal adhesion.Correspondingly,AFM imaging reveals morphological geometries of spherical cap,spreading with polygon boundaries,and elongated or polarized spreading.Membrane features are dominated by protrusions of 41-207 nm tall,short rods with 1-6 μm in length and 10.2-80.0 nm in height,and long fibrous features of 31-246 nm tall,respectively.The protrusion is attributed to local membrane folding,and the rod and fibrous features are consistent with bilayer decorating over the F-actin assemblies.Taken collectively,the reassembly of F-actin during focal adhesion formation is most likely responsible for the changes in cellular mechanics,spreading morphology,and membrane structural features.
文摘By the use of non-contact atomic force microscopy （NC-AFM） and Kelvin probe force microscopy （KPFM）, we measure the local surface potential of mechanically exfoliated graphene on the prototypical insulating hydrophilic substrate of CAF2（111）. Hydration layers confined between the graphene and the CaF2 substrate, resulting from the graphene＇s preparation under ambient conditions on the hydrophilic substrate surface, are found to electronically modify the graphene as the material＇s electron density transfers from graphene to the hydration layer. Density functional theory （DFT） calculations predict that the first 2 to 3 water layers adjacent to the graphene hole-dope the graphene by several percent of a unit charge per unit cell.
文摘Direct observation is arguably the preferred way to investigate the interactions between two molecular complexes. With the development of high speed atomic force microscopy （AFM）, it is becoming possible to observe directly DNA-protein interactions with relevant spatial and temporal resolutions. These interactions are of central importance to biology, bionanotechnology, and functional biologically inspired materials. As in all microscopy studies, sample preparation plays a central role in AFM observation and minimal perturbation of the sample is desired. Here, we demonstrate the ability to tune the interactions between DNA molecules and the surface to create an association strong enough to enable high-resolution AFM imaging while also providing sufficient translational freedom to allow the relevant protein-DNA interactions to take place. Furthermore, we describe a quantitative method for measuring DNA mobility, while also determining the individual forces contributing to DNA movement. We found that for a weak surface association, a significant contribution to the movement arises from the interaction of the AFM tip with the DNA. In combination, these methods enable the tuning of the surface translational freedom of DNA molecules to allow the direct study of a wide range of nucleo-protein interactions by high speed atomic force microscopy.
基金financially supported by the National Natural Science Foundation of China (Nos. 60406004, 60890193, and 60736033)the National Key Micrometer/Nanometer Processing Laboratory
文摘In this article, a detailed analysis of the wet- etching technique for AIGaN/GaN heterostructure using dry thermal oxidation followed by a wet alkali etching was performed. The experimental results show that the oxida- tion plays a key role in the wet-etching method and the etching depth is mainly determined by the oxidation tem- perature and time. The correlation of etching roughness with oxidation time and temperature was investigated. It is found that there exists a critical oxidation temperature in the oxidation process. Finally, a physical explanation of the oxidation procedure for A1GaN layer was given.
文摘We report on an electrostatically formed nanowire （EFN）-based sensor with tunable diameters in the range of 16 nm to 46 nm and demonstrate an EFN- based field-effect transistor as a highly sensitive and robust room temperature gas sensor. The device was carefully designed and fabricated using standard integrated processing to achieve the 16 nm EFN that can be used for sensing without any need for surface modification. The effective diameter for the EFN was determined using Kelvin probe force microscopy accompanied by three- dimensional electrostatic simulations. We show that the EFN transistor is capable of detecting 100 parts per million of ethanol gas with bare SiO2.
文摘纳米声学是近年来迅速发展的新的学科领域,旨在亚微米和纳米尺度上来"听到"和"看到"我们尚未发现的物质世界。而近场声成像技术,像扫描探针声显微术(Scanning ProbeAcoustic Microscopy,SPAM)和压电响应力显微术(Piezoresponce Force Microscopy,PFM)等,不仅具有亚微米和纳米分辨力,而且能方便地对试样微区的表面形貌,材料的力学和电学等性质进行成像,是开展纳米声学研究的有效手段。文章结合实验结果,对SPAM和PFM等近场声成像技术作了简要介绍。
基金supported by the National Basic Research Program of China(973 program)(No.2013CB932801)the National Natural Science Foundation of China(Nos.11274334 and 11374205)
文摘Studying interaction between peptides and lipid membranes is helpful for understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides, which are toxic to cells through disruption of the cell membrane. Although many efforts have been made to find out common mechanisms of the peptide-induced membrane disruption, detailed information on how the peptide's amino acid sequence affects its interaction with lipid bilayers is still lacking. In this study, three peptides termed as Pep11, P11-2, and QQ11, which share a similar backbone, were employed to explore how modifications on the peptide sequence as well as terminal groups influenced its interaction with the lipid membrane. Atomic force microscopy data revealed that the peptides could deposit on the membranes and induce defects with varied morphologies and stiffness. Fluorescence resonance energy transfer(FRET) experiments indicated that the introduction of the three peptides resulted in different FRET effects on either liquid or gel lipid membranes. DPH fluorescence anisotropy and Laurdan's generalized polarization analysis showed that P11-2 could insert into the lipid membrane and impact the lipid hydrophobic region while QQ11 influenced the order of the hydrophilic head of the lipid membrane. With these results, we have illustrated how these peptides interacted differently with the lipid membrane because of the modification of their sequences. Although these peptides did not relate to disease and antibiosis, we hope these results still could provide some clues for partly understanding the working mechanism of amyloidogenic peptides and antimicrobial peptides.
基金supported by National Institute of General Medical Sciences of the National Institutes of Health,USA(P20GM103436)National Science Foundation,USA(3048111570-15-153)~~
基金supported by the National Basic Research Program of China(2011CB932800 and 2013CB934200)Sino-British Collaboration Program(2010DFA64680)+1 种基金National Natural Science Foundation of China(20973043)Chinese Academy of Sciences(KGCX2-YW-375-3)
文摘Control of blend morphology at multi-scale is critical for optimizing the power conversion efficiency(PCE)of plastic solar cells.To better understand the physics of photoactive layer in the organic photovoltaic devices,it is necessary to gain understanding of morphology and the corresponding electronic property.Herein we report the correlation between nanoscale structural,electric properties of bulk heterojunction(BHJ)solar cells and the annealing-induced PCE change.We demonstrate that the PCE of BHJ solar cells are dramatically improved(from1.3%to 4.6%)by thermal annealing,which results from P3HT crystalline stacking and the PCBM aggregation for interpenetrated network.The similar trend for annealinginduced photovoltage and PCE evolution present as an initial increase followed by a decrease with the annealing time and temperature.The surface roughness increase slowly and then abruptly after the same inflection points observed for photovoltage and PCE.The phase images in electric force microscopy indicate the optimized P3HT and PCBM crystallization for interpenetrating network formation considering the spectroscopic results as well.From the correlation between surface photovoltage,blend morphology,and PCE,we propose a model to illustrate the film structure and its evolution under different annealing conditions.This work would benefit the better design and optimization of the morphology and local electric properties of solar cell active layers for improved PCE.
