Covalent immobilization of DNA onto functionalized mica for atomic force microscopy

The immobilization of DNA on the self-assembled monolayer of 3-aminopropyltrimethoxysilane (APTES) on mica wafer functionalized with glutaraldehyde (GA) by chemical bonding was studied by atomic force microscopy (AFM). The DNA used for our investigation was amplified by polymerase chain reaction, and primers were labeled with a -NH2 group at their 5' terminus. The surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and AFM. Results from XPS and AFM showed that the mica with the APTES and activated with GA can be formed, and the flatness of the mica can be adapted for AFM images. We found that the modified surface was capable of binding DNA molecules so that it withstood a thorough rinsing with a solution of sodium dodecylsulfate. Covalent binding between the aldehyde-terminated membrane and -NH2 groups at both ends of double-stranded DNA resulted in immobilization and straightening of the DNA.     

DNA as a template in self-assembly of Au nano-structure

In this study, an alkanethiol-assisted self-assembly of Au nano-particles and its size tunable technique were confirmed. To fabricate a one-dimensional (1D) template, -DNA was first laid on mica substrate by dropping diluted -DNA solution, 12.6?ng/[micro sign]l, on freshly cleaved mica. By dropping colloidal gold solution on mica surface with the DNA templates laid on it, the -DNA was then pulled straight via capillary force by applying solvent absorbing tissue at outer circumference of the mica substrate. Moreover, it fixed on mica via gravity force and Van der Waals force between mica surface and the DNA. Au nano-particles would be arrayed along the straight DNA molecules to form 1D Au arrays. Then based on the synthesis of 1D nano-structure via DNA template and Au nano-particles, the simple 2D nano-structure, a ring, would also be studied.     

DNA detection using a triple readout optical/AFM/MALDI planar microwell plastic chip

A ready-to-spot disposable DNA chip for specific and sensitive detection of DNA was developed. Plastic copolymeric substrate chemistry was optimized to selectively couple the target DNA with the active chip surface. At the same time, the developed substrate limits the unspecific adsorption of probe DNA molecules or additional polar contaminants in the test samples to the chip surface. The combination of glycidyl and n-butyl methacrylates was found to best fit the requirements of the assay. The fabricated DNA microarrays have mechanical properties similar to those of the glass or silicon substrates and, at the same time, provide chemically reactive surfaces that do not require lengthy chemical modification. An additional advantage of the plastic microchip is its compatibility with different analytical readout techniques, such as mass spectrometry (MALDI-TOF/MS), optical detection (fluorescence and enzyme-induced metal deposition), and imaging techniques (atomic force microscopy). These multiple readout techniques have given us the ability to compare the sensitivity, selectivity, and robustness of current state-of-the-art bioanalytical methods on the same platform exemplified by successful DNA-based detection of human cytomegalovirus. The obtained sensitivity for enzymatically enhanced silver deposition (10(-15) M) surpasses that of conventional fluorescence readouts. In addition, the assay's dynamic range (10(-6)-10(-15) M), reproducibility, and reliability of the DNA probe detection speaks for the silver deposition method. At compromised sensitivity (10(-9) M), the length of the DNA probes could be checked and, alternatively, DNA single point polymorphisms could be analyzed.     

Localized nanoscopic surface measurements of nickel-modified mica for single-molecule DNA sequence sampling

Cleaved, cation-derivatized Muscovite mica is utilized extensively in atomic force microscopy (AFM) imaging because of its flatness over large areas (millimeter cleavage planes with local root-mean-square roughness < 0.3 nm), ease of preparation, and ability to adsorb charged biomolecules such as DNA (work by Hansma and Laney, Guthold et al., and McMaster et al.). In particular, NiCl(2) treatment has become a common method for controlling DNA adsorption on mica substrates while retaining the mica's ultraflat surface (work by Pietrement et al.). While several studies have modeled the mica/metal ion/DNA system using macroscopic colloidal theory (DLVO, etc.; Pietrement et al., Sushko et al., Pastre et al., and Cheng et al.), nickel/mica's physicochemical properties have not been well characterized on the nanoscale. Efforts to manipulate and engineer DNA nanostructures would benefit greatly from a better understanding of the surface chemistry of nickel/mica. Here we present in situ nanometer- and attogram-scale measurements and thermodynamic simulation results that show that the surface chemistry of nickel-treated mica is more complex than generally appreciated by AFM practitioners because of metal-ion speciation effects present at neutral pH. We also show that, under certain preparations, nickel/mica allows in situ nanoscopic nucleotide sequence mapping within individual surface-adsorbed DNA molecules by permitting localized, controlled desorption of the double helix by soluble DNA binding enzymes. These results should aid efforts to precisely control the DNA/mica binding affinity, particularly at the physiological pH ranges required by enzymatic biochemistry (pH 7.0-8.5), and facilitate the development of more complex and useful biochemical manipulations of adsorbed DNA, such as single-molecule sequencing.     

Dynamic wettability study on the functionalized PEGylated layer on a polylactide surface constructed by the coating of aldehyde-ended poly(ethylene glycol) (PEG)/polylactide (PLA) block copolymer

A block copolymer of α-acetal-poly(ethylene glycol) and polylactide(PEG/PLA) was prepared and utilized as a surface modifier to construct a functionalized PEG layer on a PLA substrate by simple coating. An active functional group, aldehyde, was readily prepared by the derivatization of an α-acetal group at the tethered PEG-chain end and can be further utilized to link bioactive functionality molecules such as sugars and proteins. The PEGylated surface thus prepared was characterized by the method of dynamic wetting using the Wilhelmy plate technique and by the surface/interfacial free energy calculation. The results of the dynamic wetting study suggested that the interactions of PEG on the surface with water induce the reorientation of the hydrophilic PEG component to accommodate itself optimally with the water phase, resulting in a significant reduction in the interfacial free energy. By employing the extended Fowkes’ equation, the polar interactions are accurately estimated in the free energy calculation of PEGylated surface; the polar components in surface free energy may be divided into two contributions with distinctive characteristics; one is the γ_s^h component reflecting water-interactive Lewis sites and the other is the γ_s^p component reflecting the dipole moment on the surface. The γ_s^p component, related to the PEG conformation via the dipole moment on the substrate, was suggested to be a determinant factor in the protein adsorption. Because these surfaces have both non-fouling and ligand-binding properties, they might support the selective binding and the growth of particular cell populations, and eventually, they are expected to have a high utility in biomedical fields including the field of tissue engineering.     

Characterisation of FR-4 substrate with various plasma treatment conditions

Abstract

The effects of plasma treatment on the surface of the flame resistant-4 (FR-4) substrate with underfills under various treatment conditions (operating gas, operating time, operating power) are investigated by using contact angle measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The plasma treatment on substrate surfaces increased the oxygen containing functional groups or the polar component of the surface free energy, improving the wetting characteristics of the underfills/FR-4 substrates. The plasma treatment conditions which minimised the contact angle between the underfills and FR-4 substrates were an operating power of 300 W and operating time of 180 s under Ar gas atmosphere.     

氧气等离子体处理对CFRP表面特性及胶接界面力学性能的影响EI北大核心CSCD

为改善碳纤维增强复合材料(CFRP)胶接界面力学性能,采用低温氧气等离子体处理设备对CFRP进行表面处理。利用接触角测量仪、扫描电子显微镜(SEM)、原子力显微镜(AFM)、X射线光电子能谱(XPS)对CFRP表面润湿性、表面能、表面形貌、表面化学组分等进行表征,通过双悬臂梁实验(DCB)对CFRP胶接界面力学性能进行研究。结果表明:随氧气等离子体处理时间从0 s增加至30 s,表面水接触角从97°降至29°,CFRP表面润湿性达到最佳,极性分量占比显著增多;随处理时间的增加,CFRP表面粗糙度和最大高低差降低,形成较多谷峰分布的纳米级沟壑,基体表面积增大;同时,表面C—O和C■O等含氧极性官能团含量明显增加,C—C/C—H和Si—C官能团含量减少,表面污染物得到有效清除和转化;与未处理相比,经氧气等离子体处理20 s后,CFRP胶接界面最大剥离载荷和Ⅰ型断裂韧度分别提高了1.01倍(62.73 N)和1.92倍(649.21 J/m 2)。研究发现,氧气等离子体处理可以显著改善CFRP表面物理化学特性,有利于CFRP与胶黏剂更好的黏结,提高胶接界面剥离强度与韧性。     

Adsorption of anionic polyacrylamide onto coal and kaolinite: Changes of surface free energy components

The wettability of floc has a large effect on the selective flocculation flotation process of fine coal separation. The changes of thermodynamic characterization of coal and kaolinite have been investigated by Washburn dynamic method and Fourier transform infrared spectroscopy (FTIR) before and after the adsorption of anionic polyacrylamide. Lipophilic hydrophilic ratio (LHR), surface free energy, and its components were calculated by Washburn equation combined with Van Oss–Chaudhury–Good theory according to the wetting curves of coal and kaolinite samples wetted by n-hexane, α-bromonaphthalene, formamide, and water. After PAM A401 adsorption, the peaks of hydrophilic functional groups of coal (the amide group, free-NH2, secondary amide N–H, C–N) were increased, while the peaks of the hydrophobic functional group, including methyl (-CH3) and methylene (–CH2–), was decreased. The LHR value of coal decreased from 9.23 to 7.28. The polar components of coal were increased, the non-polar components were decreased, and the surface free energy was increased from 39.92 to 40.43 mN m^?1. The coal surface became more hydrophilic. For kaolinite, both hydrophilic and hydrophobic functional groups were increased, while its LHR values increased from 1.44 to 1.65. The polar component was decreased from 58.27 to 55.05 mN m^?2. Results of FTIR were corresponding to the surface property.     

剑麻纤维表面特性及其浸润行为

采用Weibull统计分布方法量化了剑麻纤维的横截面积, 并考虑液体在剑麻纤维中空结构中的芯吸质量, 发展了基于Wilhelmy吊片法原理测试剑麻纤维与液体动态接触角的表征方法。在此基础上, 分析了不同表面处理方法对剑麻纤维微观结构、 表面化学组成、 表面能及其色散、 极性特性的影响规律, 并测试了剑麻纤维与E51环氧树脂的浸润性。结果表明: NaOH、 阻燃剂处理使剑麻纤维表面极性官能团增加, 纤维的表面能极性分量增加显著; 硅烷处理增加了剑麻纤维表面的极性基团含量, 但使其极性分量减小, 表面能略有下降; 并且剑麻纤维与E51树脂的浸润性与其极性比匹配特性密切相关。     

原子力显微镜研究材料光滑表面的微摩擦性能

用原子力显微镜研究了单晶硅、云母表面的微摩擦性能,通过选择扫描角度及对分长度的方法,研究了一种有效的测试光滑材料表面微观静摩擦力的方法.结果表明,新解理云母与探针间的微观静摩擦系数和动摩擦系数均低于单晶硅的表面,但粘附力要大于单晶硅,这可能是由于新解理云母表面带有的电荷易吸收水分造成的.     

Real-time dynamics of single-DNA molecules undergoing adsorption and desorption at liquid-solid interfaces

The conformational dynamics and adsorption/desorption behavior of individual lambda-DNA molecules at liquid-solid interfaces were monitored by imaging within the evanescent field layer using total internal reflection fluorescence microscopy. At a fused-silica surface, molecular conformation and adsorption behavior were found to depend on both pH and buffer composition. A histogram of individual lambda-DNA adsorption durations measured by hydrodynamically flowing molecules along the interface exhibited asymmetry nearly identical to that of the corresponding elution peaks found in capillary liquid chromatography and capillary electrophoresis. The accessibility of the surface to the molecules, which is proportional to the capillary surface area-to-volume ratio, can be correlated with the capacity factor and the relative adsorption factor. At a C18 surface, the dynamics of individual DNA molecules changed with the addition of organic solvent as well as with pH. Hydrophobic interaction rather than electrostatic interaction was the major driving force for adsorption of individual DNA molecules.     

The morphology of isotactic polystyrene crystals grown in thin films: the effect of substrate material

Thin isotactic polystyrene films (∼50 nm thick) have been crystallized from the melt on various substrate materials (carbon, glass, mica, polyimide sheet and silicon). The morphology of the crystals has been examined using atomic force microscopy, and was found to be dependent on the nature of the substrate, with two basic types of crystal forming. Crystals either develop around giant screw dislocations, or around small bundles of lamellae growing perpendicular to the substrate surface. It has further been observed that the number of screw dislocations generated in the lamellae is also dependent on the substrate, as is the growth rate of the spiral terraces. These effects are interpreted in terms of interactions between the molecules in the melt and the substrate surface. This revised version was published online in November 2006 with corrections to the Cover Date.     

轨梁辊矫过程矫直力波形分析与工程算法

针对辊式矫直机常规理论计算方法的缺陷及矫直力实测中难于直接测量辊系中所有辊子矫直力的困难,通过对国内首台巨型1 300矫直机矫直力的工程测试和上排辊矫直力的波形分析,按压力阶梯（矫直力分量）剖析了矫直力和矫直过程,揭示了超静定矫直力系的建立过程和各辊矫直力之间的力学关系,拟定了矫直力系和矫直力分量的分割单元测量原理和总体便捷的工程测试方法,给出了以矫直力矩和压力阶梯表示的矫直力通式及其工程算法,并提供了计算工-56及轨-50矫直力的诺模图。这种确定矫直力的原理和方法,可供各种重型辊式矫直机工程应用。     

Unconventional nanotubes self-assembled in alumina channels: morphology and surface potential of isolated nanostructures at surfaces

Synthetic nanographenes have been self-assembled from solution on the surface of nanometric channels of an alumina membrane template. By controlling the interplay between intermolecular and interfacial interactions, the molecules have been adsorbed either 'face-on' or 'edge-on' on the pore's surfaces, leading to the formation of columnar stacks in the latter case. Upon thermal treatment at high temperature, the molecular cross-linking of the columns has been triggered, transforming the delicate supramolecular arrangement into robust carbon nanotubes, with the graphitic planes at predetermined orientations with respect to the tube axis. Scanning force microscopy characterization of single nanotubes deposited from suspensions on mica showed that the nanotubes can self-assemble on flat surfaces adopting preferential alignments which reflect the threefold symmetry of the mica substrate. Kelvin probe force microscopy studies revealed that the nanotubes possess a surface potential much smaller than the work function of both graphite and conventional vacuum-processed nanotubes, providing evidence for their more confined electronic structure.     

Detection of Single DNA Molecule Hybridization on a Surface by Atomic Force Microscopy

Improving the detection of DNA hybridization is a critical issue for several challenging applications encountered in microarray and biosensor domains. Herein, it is demonstrated that hybridization between complementary single‐stranded DNA (ssDNA) molecules loosely adsorbed on a mica surface can be achieved thanks to fine‐tuning of the composition of the hybridization buffer. Single‐molecule DNA hybridization occurs in only a few minutes upon encounters of freely diffusing complementary strands on the mica surface. Interestingly, the specific hybridization between complementary ssDNA is not altered in the presence of large amounts of nonrelated DNA. The detection of single‐molecule DNA hybridization events is performed by measuring the contour length of DNA in atomic force microscopy images. Besides the advantage provided by facilitated diffusion, which promotes hybridization between probes and targets on mica, the present approach also allows the detection of single isolated DNA duplexes and thus requires a very low amount of both probe and target molecules.     

Atomic force microscopic observation of the molecular orientation in ultrathin films of alkanoic acid-derivatized porphyrins on a mica surface

The observation of the molecular orientation of alkanoic acid-derivatized porphyrins in ultrathin films deposited on mica was carried out by atomic force microscopy. It was observed that the tetraacid derivative 5, 10, 15, 20-tetra(N-10-carboxydecyl-pyridinium-4-yl) porphyrin was arranged as a monolayer with the porphyrin macrocycle oriented coplanar to the mica surface. On the other hand, the diacid derivative protoporphyrin IX Zn(II) formed a bilayer with the hydrophobic part inside and the hydrophilic part in the periphery. Therefore, in this case, the porphyrin macrocycle is roughly perpendicular to the mica surface.     

How flat is an air-cleaved mica surface?

Muscovite mica is an important mineral that has become a standard substrate, due to its easy cleavage along the {001} planes, revealing a very flat surface that is compatible with many biological materials. Here we study mica surfaces by dynamic atomic force microscopy (AFM) operated in the non-contact mode (NC-AFM) under ultra-high vacuum (UHV) conditions. Surfaces produced by cleaving in UHV cannot be imaged with NC-AFM due to large surface charges; however, cleavage in air yields much less surface charge and allows for NC-AFM imaging. We present highly resolved NC-AFM images of air-cleaved mica surfaces revealing a rough morphology originating from a high density of nanometre-sized particles. Among these particles, we find regularly shaped structures indicating the growth of crystallites on the surface. The contamination layer cannot be removed by degassing in UHV; even prolonged heating at a temperature of 560?K under UHV conditions does not yield an atomically flat surface.     

粗化液中钯离子对ABS塑料直接电镀的影响

粗化是实现活化液在ABS表面吸附的前提和获得良好结合力的必要条件.采用含痕量钯离子的铬酐-硫酸粗化液对ABS塑料表面进行化学粗化,用AFM、XPS和胶体钯吸附量等对粗化前后塑料的表面性能、价键状态和活性进行了考察.结果表明:钯离子加入到粗化液中对ABS表面的粗糙度影响不显著,粗化后的表面氧含量升高;随着粗化液中钯离子浓度的增加,胶体钯在ABS表面上的吸附量增加;增加粗化液中的Pd含量可使ABS表面在低浓度胶体钯溶液中达到与高浓度钯相同的吸附量,有效地降低了胶体钯的浓度.粗化液中加入钯离子不影响基体与镀层的结合力.     

Effect of amino-terminated substrates onto surface properties of cellulose esters and their interaction with lectins

Films of cellulose acetate butyrate (CAB) and carboxymethylcellulose acetate butyrate (CMCAB) were deposited from ethyl acetate solutions onto bare silicon wafers (Si/SiO₂) or amino-terminated surfaces (APS) by means of equilibrium adsorption. All surfaces were characterized by means of ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The presence of amino groups on the support surface favored the adsorption of CAB and CMCAB, inducing the orientation of most polar groups to the surface and the exposition of alkyl group to the air. Such molecular orientation caused increase of the dispersive component of surface energy (γ_s^d) and decrease of the polar component of surface energy (γ_s^p) of cellulose esters in comparison to those values determined for films deposited onto bare Si/SiO₂ wafers. Adsorption behavior of jacalin or concanavalin A onto CAB and CMCAB films was also investigated. The adsorbed amounts of lectins were more pronounced on cellulose esters with high (γ_s^p) and total surface energy (γ_s^t) values.     

基体诱导法制备碳纳米管/云母复合导电粉

基体诱导法制备碳纳米管(CNT)/云母复合导电粉, 即用聚乙烯醇(PVA)或聚丙烯酰胺(PAM)对云母进行处理, 将处理后的云母与CNT分散液混合, 使CNT吸附在云母表面. 测试复合导电粉的体积电阻率(ρ)发现, CNT含量为1.0wt%时, CNT/云母的ρ为2.0×10⁴Ω·cm, 而用PVA修饰的云母制备CNT/云母, 体积电阻率达到86.6Ω·cm. 运用XPS、SEM对复合导电粉进行表征. 结果表明当云母表面经PVA修饰后, 能改善CNT在其表面的吸附和分散, 使CNT/云母的体积电阻率明显降低.