Fibrinogen adsorption on three silica-based surfaces: conformation and kinetics

Using AFM (atomic force microscopy) to probe protein conformation and arrangement, and TIRF (total internal reflectance fluorescence) to monitor kinetics, fibrinogen adsorption on three different silica-based surfaces was studied: the native oxide on silicon, acid-etched microscope slides, and acid-etched polished glass. The three are chemically similar, but the microscope slide is rougher and induces AFM tip instabilities that appear as high spots on the bare surface. Fibrinogen's conformation and transport-limited adsorption kinetics are found to be quantitatively similar on all three surfaces. Further, the number of adsorbed proteins in progressive AFM micrographs quantitatively match the coverages measured by TIRF during early adsorption. Surfaces appear full, via AFM, when adsorbed amounts are about an order of magnitude below their true saturation levels (via TIRF) because, above about 0.26 mg/m(2), individual proteins cannot be discerned. The results demonstrate how the appearance of AFM micrographs can be misleading regarding surface saturation. On all three surfaces, fibrinogen is, at most, slightly aggregated, showing limited, if any, surface mobility. The complexities of the microscope slide's surface landscape minimally impact adsorption.     

Structure and Growth of Two-dimensional Ices at the Surfaces Probed by Scanning Probe Microscopy

Scanning probe microscopy(SPM) stands out as one of the most powerful tools for characterizing the solid surface and the adsorbed molecules with ?ngstr?m resolution in real space. In particular, this unique technique provides an unprecedented opportunity for directly probing the low-dimensional ices at surfaces. In this perspective, we first review the recent advances of scanning tunneling microscopy(STM) imaging of various two-dimensional(2 D) ice structures on metal[1-7], insulator[8-12], graphite[13-15] surfaces and under strong confinement[10, 16-19]. We then introduce that noncontact atomic-force microscopy(AFM) with a CO-terminated tip enables atomic imaging of a genuine 2 D ice grown on a hydrophobic Au(111) surface with minimal perturbation[20], paying particular attention to the growth processes at the edges of 2 D ice. In the end, we present an outlook on the future applications of 2 D ice as well as the relation between the 2 D and 3 D ice growth.     

预沉积Ge对Si(111)衬底上SSMBE外延生长SiC薄膜的影响

利用固源分子束外延(SSMBE)生长技术, 在Si(111)衬底上预沉积不同厚度(0、0.2、1 nm)Ge, 在衬底温度900 ℃, 生长SiC单晶薄膜. 利用反射式高能电子衍射仪(RHEED)、原子力显微镜(AFM)和傅立叶变换红外光谱(FTIR)等实验技术, 对生长的样品进行了研究. 结果表明, 预沉积少量Ge(0.2 nm)的样品, SiC薄膜表面没有孔洞存在, AFM显示表面比较平整, 粗糙度比较小, FTIR结果表明薄膜内应力比较小. 这说明少量Ge的预沉积抑制了孔洞的形成, 避免衬底Si扩散, 因而SiC薄膜的质量比较好. 没有预沉积Ge的薄膜, 结晶质量比较差, SiC薄膜表面有孔洞且有Si存在. 然而预沉积过量Ge (1 nm) 的样品, 由于Ge的岛状生长,导致生长的SiC表面粗糙度变大, 结晶质量变差, 甚至导致多晶产生.     

Synthesis of Ni／Mg／Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni) : n(Mg) : n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [ n( Ni)/n( Mg)/n(Al) = 1/1/1 ] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.     

Gold nanoparticle arrays directly grown on nanostructured indium tin oxide electrodes: Characterization and electroanalytical application

This work describes an improved seed-mediated growth approach for the direct attachment and growth of mono-dispersed gold nanoparticles on nanostructured indium tin oxide (ITO) surfaces. It was demonstrated that, when the seeding procedure of our previously reported seed-mediated growth process on an ITO surface was modified, the density of gold nanospheres directly grown on the surface could be highly improved, while the emergence of nanorods was restrained. By field emission scanning electron microscopy (FE-SEM) and cyclic voltammetry, the growth of gold nanoparticles with increasing growth time on the defect sites of nanostructured ITO surface was monitored. Using a [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox probe, the increasingly facile heterogeneous electron transfer kinetics resulting from the deposition and growth of gold nanoparticle arrays was observed. The as-prepared gold nanoparticle arrays exhibited high catalytic activity toward the electrooxidation of nitric oxide, which could provide electroanalytical application for nitric oxide sensing.     

Synthesis and manipulation of high aspect ratio gold nanorods grown directly on surfaces

Here we describe the synthesis of Au nanorods directly on glass surfaces using seed-mediated deposition of Au from AuCl4- onto surface-attached 3-5 nm diameter Au nanoparticles (AuNPs) in the presence of cetyltrimethylammonium bromide (CTAB). The average length (200 nm to 1.2 microm) and aspect ratio (6-22) of the nanorods increases with increasing AuCl4- concentration. Short, low aspect ratio Au nanorods are manipulated with an atomic force microscopy (AFM) tip, while longer, high aspect ratio nanorods are bent and broken with the AFM tip.     

Growth and characterization of ZnO nanowire arrays electrodeposited into anodic alumina templates in DMSO solution

ZnO nanowire arrays were grown by potentiostatic cathodic electrodeposition on aluminum anodic oxide template (AAO) from dimethyl sulfoxide (DMSO) solutions containing zinc chloride and molecular oxygen as precursors. The nanowires presented high aspect ratio and exhibited a very high crystallinity with a wurtzite crystal structure with preferential orientation along the (0001) crystallographic axis. Chronoamperometric experiments were performed on gold bulk electrodes in order to model this preferential mode growth of ZnO nanowires, which has not been previously reported for similar precursors in DMSO solution. The analysis of the corresponding chronoamperograms revealed that chloride ions influence the oxide nucleation and growth mechanism. It was found that in the absence of KCl as a supporting electrolyte, the data fitted an instantaneous three-dimensional diffusion-controlled (IN-3D)_diff nucleation and growth mechanism (NGM). The presence of KCl, instead favored a progressive three-dimensional (PN-3D)_diff NGM. With these results, a model for the more complex nanowire’s growth inside the pores of the AAO template is proposed.     

Nucleation and growth of gas barrier aluminium oxide on surfaces of poly(ethylene terephthalate) and polypropylene: effects of the polymer surface properties

The nucleation and initial stages of growth of aluminium oxide deposited on two different polymer surfaces [poly(ethylene terephthalate), (PET) and amorphous polypropylene, (PP)] have been studied by atomic force microscopy (AFM). The permeation of water vapor and oxygen through the films has been measured. The initial stages of the growth of the oxide consisted of separated islands on the polymer surface. Further growth of oxide depends strongly on the surface morphology and chemical nature of the polymer surface. Growth on PET follows a layer‐by‐layer mechanism that maintains the native surface roughness of the polymer substrate. Growth on PP, however, follows an island mode, which leads to an increase in surface roughness. This may be due to a lack of chemical bonding between the polymer and the arriving metal–oxygen particles. The oxide layer on PET grows more densely than on PP, providing superior barrier to gas permeation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3151–3162, 2000     

Controlled growth of semiconducting oxides hierarchical nanostructures

Semiconducting ZnO hierarchical nanostructure, where ZnO nanonails were grown on ZnO nanowires, has been fabricated under control experiment with a mixture of ZnO nanopowders and Sn metal powders. Sn nanoparticles are located at or close to the tips of the nanowires and the growth branches, serving as the catalyst for the vapor-liquid-solid growth mechanism. The morphology and microstructure of ZnO nanowire and nanonail were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The long and straight ZnO nanowires grow along [0001] direction. ZnO nanonails are aligned radially with respect to the surface the ZnO nanowire. The long axis direction of nanonails forms an angle of ∼30° to the [0001] direction.     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理Ⅰ.PMNT单晶的表面形貌、负晶结构及生长基元的组装与拆分

铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO_6]配位八面体,晶体生长过程可视为多种八面体基元与Pb~(2 )的组装过程.这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌.Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似“蚀象”的构型,这些可从[BO_6]八面体生长基元的组装或拆分方面获得解释.     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理1: PMNT单晶的表面形貌 、负晶结构及生长基元的组装与拆分

铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO~6]配位八面体,晶体生长过程可视为多种八面体基元与Pb^2^+的组装过程。这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌。Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似"蚀象"的构型,这些可从[BO~6]八面体生长基元的组装或拆分方面获得解释。     

原子力显微镜针尖诱导聚氧乙烯熔体结晶的研究

原子力显微镜(AFM)是研究高分子结晶行为的一种重要实验手段.在使用AFM原位观察高分子结晶时,为保证能真实地反映结晶过程,一个必须注意的问题是要避免AFM针尖的影响.与此同时,人们考察了在AFM扫描时针尖诱导高分子结晶成核的情况.若使用AFM接触模式(contactmode),扫描时容易造     

Evaluation of the adhesion properties of inorganic materials with high surface energies

With the aim of checking the validity of methods for characterizing the adhesion between inorganic materials with high surface energies, the properties of the adhesion between an inorganic material (indium tin oxide (ITO)) and model surfaces with various surface energies (Cl-, NH2-, CH(3)-, and CF3-functionalized surfaces) were evaluated using atomic force microscopy (AFM) and the Johnson-Kendall-Roberts (JKR) apparatus. For this purpose, the AFM tip and the JKR lens were modified with ITO using radio frequency (rf) magnetron sputtering. The work of adhesion between the ITO coating and each model surface was estimated using AFM and the JKR apparatus and compared with the result obtained from contact angle measurements. The adhesion forces determined from the force-displacement curves (AFM) were found to agree with the predictions of the Derjaguin-Muller-Toporov (DMT) theory. The JKR equation used in the interpretation of the JKR experiments was modified by taking into account the differences between the surface and bulk moduli of the ITO-coated poly(dimethylsiloxane) (PDMS) lens. The ratio of the surface modulus to the bulk modulus we used in this modified JKR equation was obtained by determining the slope of the attracting part of the force-displacement curve. The values of the work of adhesion calculated using the modified JKR equation were also found to agree with the values obtained from contact angle measurements. We conclude that the two methods using AFM and the JKR apparatus can be used in the evaluation of the work of adhesion between inorganic materials with high surface energies such as metal and metal oxide surfaces.     

Imaging of reconstituted purple membranes by atomic force microscopy

The organization of bacteriorhodopsin (bR) within reconstituted purple membranes (RPM) was examined using atomic force microscopy (AFM). Five reconstituted species were examined: RPM 3 (bR/native polar lipids/dimyristoylphosphatidylcholine (DMPC) in a 1:9:14 molar ratio), RPM 4 (bR/native polar lipids in a 1:7 molar ratio), RPM 5 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycerol in a 1:3.5:6.1 molar ratio), RPM 6 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycero-3-phosphocholine in a 1:3.5:4.9 molar ratio), and RPM 7 (bR/native polar lipids/1,2-diphytanoyl-sn-glycero-3-[phospho-l-serine] in a 1:3.5:4.6 molar ratio). RPM 3 patches adsorbed onto mica exhibit domains of crystallized bR trimers arranged in a hexagonal packing structure, similar to those found in native purple membrane (NPM). These domains are enclosed by DMPC-rich regions. RPM 4 patches were observed to have larger domains of crystallized bR, with trimer orientation 30° different from that found in NPM. The bR-rich domains are enclosed by a large, protein-free, lipid-rich region. The topography of RPM 5 was difficult to resolve as the surface had no discernable patterns or structure. The topographies of RPM 6 and 7 were similar to that found in RPM 3 in that higher domains were formed within the patch adsorbed onto mica. They may contain protein-rich regions, but clear images of protein arrangement could not be obtained using AFM. This may be a result of imaging limitations or of the lack of organization of bR within these domains.     

Building a novel vitronectin assay by immobilization of integrin on calixarene monolayer

Membrane proteins possess significant hydrophobic domains and are likely to deplete their native activity immobilized on the solid surface relative to those occurring in a membrane environment. To investigate an efficient immobilization method, calix[4]crown-ether monolayer as an artificial protein linker system was constructed on the gold surface and characterized by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS), atomic force microscopy (AFM) and cyclic voltammetry (CV). Integrin alpha(v)beta3 was functionally immobilized onto the monolayer and the integrin-vitronectin interaction was investigated by surface plasmon resonance (SPR). It was found that calix[4]crown-ether was assembled as a monolayer on the gold surface. Orientation and accessibility of integrin alpha(v)beta3 was assessed by sensitive binding of its natural ligand, vitronectin at pg mL(-1) level. Moreover, surface coverage of integrin layer and thickness calculated through SPR curve simulation verified that integrin layer was a monolayer in activated form. In combination with the SPR method, this calix[4]crown monolayer provided a reliable and simple experimental platform for the investigation of isolated membrane proteins under experimental conditions resembling those of their native properties.     

The synthesis and optical properties of different zinc oxide nanostructures

The tetrapod-like whiskers (T-ZnO), nanoaeroplanes, nanocombs, nanobelts, bead-like nanoforms and many other forms of hexagonal zinc oxide were synthesized by the chemical deposition process (CVD). From the experimental results it can be seen that the composition of source gases and the speed of oxidation are essential to the growth of each of these morphologies of zinc oxide. By controlling the growth conditions, one novel morphology of ZnO (bead-like nanoform) has been obtained. The ZnO tetrapod-like whiskers were grown without catalysts on the walls of quartz tube. The structure and morphology of the T-ZnO was characterized. All four legs of as-grown ZnO nanotetrapods are needle-like and hexagonal shaped and grow in the ±[0001] direction. The effect of synthesis conditions on the morphology and size T-ZnO was observed. Possible mechanisms of growth were investigated. The lengths of the legs of the tetrapods range from 1 to 15 μm and diameter varying from 0.03 to 1 μm during the synthesis. In the photoluminescence spectra T-ZnO clearly shows two maxima at UV and visible regions. The oxygen impurity, particularly, oxygen flow rates mainly influences on increasing (decreasing) at PL peaks. The maximum near of 590–610 nm (～2 eV), confirming the influence of native defects (oxygen vacancies and interstitials) on the PL intensity and optical quenching exciton peak.     

A simple route to synthesize scales of aligned single-crystalline SiC nanowires arrays with very small diameter and optical properties

Scales of aligned single-crystalline SiC nanowires (SiCNWs) arrays with very small diameter were synthesized by a simple thermal evaporation of ZnS and carbon on silicon wafer. The as-received SiCNWs possess a uniform size distribution centered at approximately 8.0 nm, even with a minimum of approximately 3.0 nm. The highly oriented SiCNWs usually grew along [111] direction with a clean surface, very thin oxide shell, and small quantity of stacking faults. A crystalline tube-like SiC nanostructure is also obtained. The optical properties, including photoluminescence and Raman scattering spectra of the SiCNWs, were investigated, respectively. In the end, a growth model on basis of the experimental data is suggested.     

In situ chemical reductive growth of platinum nanoparticles on indium tin oxide surfaces and their electrochemical applications

Platinum nanoparticles directly attached to indium tin oxide (PtNP/ITO) were successfully fabricated by using an in situ chemical reductive growth method. In this method, PtNPs could be grown on the ITO surface via the one-step immersion into the growth solution containing PtCl4(2-) and ascorbic acid. The attached and grown PtNPs were spherical having an agglomerated nanostructure composed of small nanoclusters. From the morphological changes depending on the growth time, which were observed with an FE-SEM, PtNPs were found to be grown via the progressive nucleation mechanism. As the characteristics of the PtNP/ITO were those of a working electrode, it was found that the charge transfer resisivity was significantly lowered due to the grown PtNPs. Hence, for a typical redox system of [Fe(CN)6]3-/[Fe(CN)6]4-, the PtNP/ITO electrode exhibited the electrochemical responses similar to those of the bulk Pt electrode. Furthermore, it was clarified that the PtNP/ITO electrode had significant electrocatalytic properties for the oxygen reduction and methanol oxidation. The present PtNPs that had the agglomerated nanostructure may be promising for a new type of electrode material.     

Molecular dynamics simulations of the effect of the composition of calcium alumino-silicate intergranular films on alumina grain growth

Molecular dynamics simulations were performed to study the effect of the composition of the intergranular film (IGF) on anisotropic and isotropic grain growth in alpha-Al2O3. In the simulations, the IGF is formed while in contact with two differently oriented alumina crystals, with the alumina (0001) basal plane on one side and the (110) prism plane on the other. Five different compositions in the IGFs were studied. Results show preferential growth along the [110] of the (110) surface in comparison to growth along the [0001] direction on the (0001) surface for compositions near a Ca/Al ratio of 0.5. Such preferential growth is consistent with anisotropic grain growth in alumina, where platelets form because of faster growth of the prism orientations than the basal orientation. The simulations also show the mechanism by which Ca ions in the IGF inhibit growth on the basal surface. At compositions with high or low Ca/Al ratios, growth along each surface normal is equivalent, indicating isotropic grain growth, although the attachment rates are quite different, which may indicate differences between normal grain growth and abnormal, but isotropic, grain growth. The simulations provide an atomistic view of attachment onto crystal surfaces, affecting grain growth in alumina.     

Alternative method for fabricating chemically functionalized AFM tips: silane modification of HF-treated Si3N4 probes

An alternative method for fabricating functionalized, atomic force microscopy (AFM) tips is presented. This technique is simple and requires only minimal preparation and tip modification to generate chemically sensitive probes that have a robust organic monolayer of flexible terminal chemistry attached to the surface. Specifically, commercially microfabricated Si3N4 AFM tips were modified with self-assembled monolayers (SAMs) of octadecyltrichlorosilane and (11-bromoundecyl)trichlorosilane after removing the native silicon oxide surface layer with concentrated hydrofluoric acid. The structure of these SAM films on solid silicon nitride surfaces was studied using contact angle goniometry and Fourier transform infrared spectroscopy. Pull-off force measurements on various bare (mica, graphite, and silicon) and SAM-functionalized substrates confirm that mechanically robust, long-chain organic silane SAMs can be formed on HF-treated Si3N4 tips without the presence of an intervening oxide layer. Adhesion experiments show that the integrity of the organic film on the chemically modified tips is maintained over repeated measurements and that the functionalized tips can be used for chemical sensing experiments since strong discrimination between different surface chemistries is possible.