Recognition-directed orthogonal self-assembly of polymers and nanoparticles on patterned surfaces

We demonstrate the patterning of silica substrates with thymine (Thy-PS) and positively charged N-methylpyridinium (PVMP) polymers using photolithography and the subsequent orthogonal modification of these surfaces using diaminopyridine-functionalized polystyrene (DAP-PS) and carboxylate-derivatized CdSe/ZnS core-shell nanoparticles (COO-NP) through diamidopyridine-thymine three-point hydrogen bonding and pyridinium-carboxylate electrostatic interactions, respectively. This two-component orthogonal surface modification was accomplished in a self-sorting, single-step fashion, providing a versatile tool for the rapid and efficient creation of complex materials.     

Chemical modifications of Au/SiO2 template substrates for patterned biofunctional surfaces

The aim of this work was to create patterned surfaces for localized and specific biochemical recognition. For this purpose, we have developed a protocol for orthogonal and material-selective surface modifications of microfabricated patterned surfaces composed of SiO(2) areas (100 μm diameter) surrounded by Au. The SiO(2) spots were chemically modified by a sequence of reactions (silanization using an amine-terminated silane (APTES), followed by amine coupling of a biotin analogue and biospecific recognition) to achieve efficient immobilization of streptavidin in a functional form. The surrounding Au was rendered inert to protein adsorption by modification by HS(CH(2))(10)CONH(CH(2))(2)(OCH(2)CH(2))(7)OH (thiol-OEG). The surface modification protocol was developed by testing separately homogeneous SiO(2) and Au surfaces, to obtain the two following results: (i) SiO(2) surfaces which allowed the grafting of streptavidin, and subsequent immobilization of biotinylated antibodies, and (ii) Au surfaces showing almost no affinity for the same streptavidin and antibody solutions. The surface interactions were monitored by quartz crystal microbalance with dissipation monitoring (QCM-D), and chemical analyses were performed by polarization modulation-reflexion absorption infrared spectroscopy (PM-RAIRS) and X-ray photoelectron spectroscopy (XPS) to assess the validity of the initial orthogonal assembly of APTES and thiol-OEG. Eventually, microscopy imaging of the modified Au/SiO(2) patterned substrates validated the specific binding of streptavidin on the SiO(2)/APTES areas, as well as the subsequent binding of biotinylated anti-rIgG and further detection of fluorescent rIgG on the functionalized SiO(2) areas. These results demonstrate a successful protocol for the preparation of patterned biofunctional surfaces, based on microfabricated Au/SiO(2) templates and supported by careful surface analysis. The strong immobilization of the biomolecules resulting from the described protocol is advantageous in particular for micropatterned substrates for cell-surface interactions.     

Alpha-activation analysis of boron on Si surface and in Si and SiO2 films

Brazil has become the largest producer of biomass ethanol derived from sugar cane. The industrial production is based on the fermentation of sugar cane juice by yeast, inside of large volume vats, in a fed-batch process that recycles yeast cells. To study the dynamics of chemical elements in each operating cycle, five stages of the fementation process were considered: must, yeast suspension, wine, non-yeast wine and yeast cream. For this, a mass balance of the terrigenous elements, Ce, Co, Cs, Eu, Fe, Hf, La, Na, Sc, Sm, and Th, and the sugar cane plant elements, Br, K, Rb, and Zn, were established in fementation vats of an industrial scale unit, with sampling undertaken during different climatic conditions (dry and rainy periods). A similar distribution of the sugar cane characteristics elements was found for the stages analysed, while for the terrigenous elements a trend of accumulation in the yeast cream was observed. Preferential absorption of Br, K, Rb, and Zn by yeast cells was indicated by the smaller concentrations observed in yeast suspension than in yeast cream.     

Anisotropic polymerization of a long-chain diacetylene derivative Langmuir-Blodgett film on a step-bunched SiO2/Si surface

Alternating facet/terrace nanostructures were fabricated on a SiO2 surface by step-bunching and thermal oxidation of a vicinal Si(111) substrate, and their influence upon the polymerization direction of a long-chain diacetylene derivative monolayer film was investigated by angle-dependent polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. It was found that the peak intensity of the C 1s-pi transition was stronger when the electric vector plane of the incident X-ray was parallel to the direction of the periodic facet/terrace structures rather than perpendicular to them. On the contrary, a polymer film fabricated on a flat SiO2 surface showed no in-plane anisotropy of the peak intensity. These results indicate that the diacetylene groups in the diacetylene derivative monolayer are preferentially photopolymerized in the direction not across but along the periodic one-dimensional structures on the step-bunched and thermally oxidized SiO2/Si(111) surface.     

Photoluminescence from (Si/SiO2)n superlattices and their use as emitters in [SiO2/Si]n SiO2 [Si/SiO2]m microcavities

Si/SiO2 superlattices are recently under investigation to add optical functionality to silicon based microelectronics. In such superlattices quantum-confinement should drive Si to become a good light emitter. Emission properties can be further improved and controlled by placing the emitter in optical microcavities. In this paper emission properties of (Si/SiO2), superlattices grown by Low Pressure Chemical Vapour Deposition will be compared with the ones obtained by other growth techniques and the origin of the emission will be discussed. Emission properties can be further improved and controlled by placing the emitter in optical microcavities. Optical properties of microcavities produced with standard complementary metal-oxide-semiconductor techniques containing Si/SiO2 superlattices as light emitter will be reviewed and a comparison between properties estimated from calculations and experiments will be given.     

The self-assembly of asymmetric block copolymers in films contacting a patterned surface

The preparation of ordered high-density polymer layers via the combined method of templated self-assembly is discussed. This approach combines the advantages of guided self-assembly of block copolymers and lithography on a topographical or chemical pattern. To implement the approach, a simulation has conducted for the first time through the use of the dissipative particle dynamics method in the NPAT ensemble. The pattern replication by asymmetric copolymers that form cylindrical phases in the bulk owing to their self-assembly near the patterned surface is studied. The effects of three patterns are described, i.e., hexagonal, rectangular, and triangular, which are characterized by one or two length scales. It is shown that the dense hexagonal pattern and the sparse rectangular and triangular patterns induce vertically oriented cylindrical domains in a thin film. The control of the orientation and ordering in the formed morphology heavily depends on the interaction between the minority component and the pattern. This effect is global in nature: The surface pattern propagates into the bulk of a film. In the case of rectangular and triangular patterns, two- and fourfold increases in their quantitites in the bulk are observed.     

In situ surface-enhanced infrared absorption spectroscopy for the analysis of the adsorption and desorption process of Au nanoparticles on the SiO2/Si surface

The adsorption and desorption of Au nanoparticles (AuNP) in colloidal D2O suspension on the (3-aminopropyl)triethoxysilane treated SiO2/Si surface was investigated by in situ attenuated total reflection surface enhanced infrared absorption (ATR-SEIRA) spectroscopy with a liquid flow cell. With increasing surface density of AuNP, the absorption of the vibrational modes of D2O and of the citrate molecules covering the AuNP increases due to SEIRA. Repulsive electrostatic Coulomb forces between the AuNP lead to the saturation of the AuNP surface density at submonolayer coverage. We show that the adsorption kinetics can be investigated by monitoring in situ the molecular vibrational modes of D2O and the citrate molecules. Furthermore, we clarify that the adsorption process can be described very well by a diffusion-limited first-order Langmuir kinetics model. When exposing a saturated AuNP submonolayer to 2-aminoethanethiol (AET)/D2O solution, the AuNP are removed from the surface and the IR absorption of the D2O vibrational modes become weaker again. Taking into account the time dependencies of the OD and the CH peaks, we propose a microscopic model where the AET molecules quickly adsorb on the AuNP by replacing most of the precovering citrate molecules exposed to the AET solution. As this takes place, the AuNP agglomerate-as we could detect with scanning electron microscopy-and are finally removed from the surface.     

Au adatoms in self-assembly of benzenethiol on the Au(111) surface

Self-assembly of benzenethiol at low coverage on Au(111) was studied using low-temperature scanning tunneling microscopy. Phenylthiolate species (PhS), formed by thermal dehydrogenation of the parent PhSH molecule, was found to self-assemble into surface-bonded complexes with gold adatoms. Each complex involves two PhS species and one gold adatom. The PhS species form either cis- or trans-geometry relative to each other. At a higher coverage, the complexes coalesce, most likely due to the formation of weak C-H...S hydrogen bonds facilitated by the spatial arrangement of the PhS groups. Our findings thus establish that the self-assembly of arenethiols on the Au(111) surface is driven by gold adatom chemistry, which has recently been found to be the key ingredient in the self-assembly of alkanethiols on gold.     

Fabrication of polydiacetylene nanowires by associated self-polymerization and self-assembly processes for efficient field emission properties

The paper described here concerns a challenge of general interest for producing a novel structure of a polymer aggregate, the achievement of nanowires with controlled diameters. We provide a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes. The polymer nanowire film shows excellent field emission properties with the turn-on field of 8.2 V/mum at 10 muA/cm2 and the maximum current density of 5 mA/cm2 at an applied field of 15 V/mum.     

PDDA/SnTsPc静电自组装膜的制备及其形态研究

采用静电层-层自组装技术制备出了含有阴离子磺化酞菁锡(SnTsPc)和阳离子聚二烯丙基二甲基胺盐酸盐(PDDA)交替复合超薄膜.利用紫外-可见光谱表征了PDDA/SnTsPc多层膜的组装过程,表明薄膜的吸收是连续的、有规律的.原子力结果表明,膜表面是光滑的、均匀的;在膜表面紧密堆积的纳米粒子的平均粒径为53.1 nm,平均表面粗糙度是4.021 nm.     

Fabrication of glucose biosensor for whole blood based on Au/hyperbranched polyester nanoparticles multilayers by antibiofouling and self-assembly technique

Acknowledging the benefits of hyperbranched polymers and their nanoparticles, herein we report the design and synthesis of sulfonic acid group functionalized hydroxyl-terminated hyperbranched polyester (H30-SO₃H) nanoparticles and their biomedical application. The H30-SO₃H nanoparticles were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance spectroscopy (¹H NMR). The good hemocompatibility of H30-SO₃H nanoparticles was also investigated by coagulation tests, complement activation and platelet activation. The novel glucose biosensor was fabricated by immobilizing the positively charged Au nanoparticles, H30-SO₃H nanoparticles and glucose oxidase (GOx) onto the surface of glassy carbon electrode (GCE). It can be applied in whole blood directly, which was based on the good hemocompatibility and antibiofouling property of H30-SO₃H nanoparticles. The biosensor had good electrocatalytic activity toward glucose with a wide linear range (0.2–20 mM), a low detection limit 1.2 × 10⁻⁵ M in whole blood and good anti-interference property. The development of materials science will offer a novel platform for application to substance detection in whole blood.     

Pt／Ti／Si3N4／SiO2／Si基底的多层薄膜制备及拉曼研究

选用三水醋酸铅、乙酰基丙酮酸锆、四异丙氧基钛、乙酰丙酮作初始材料,用同样的方法分别制备了锆钛酸铅（PZT）和钛酸铅（PT）两种固体前驱物．采用改良型的溶胶-凝胶工艺技术,分别在不同的Pt-Ti-Si3N4-SiO2-Si基底上,按照不同的组合方式,制备了三种多层薄膜：PZT、PT／PZT—PZT／PT、PT／PZT／-／PZT／PT．较详细地讨论了薄膜制备的工艺技术,发现当凝胶通过烧结和干燥后变成固态物质时,薄膜内部存在着较大的残余应力,当薄膜在600℃下退火时其内部残余应力可以被减小．通过拉曼衍射和XRD分析,发现PT／PZT—PZT／PT结构的薄膜具有较好的结晶性和较小的残余应力．XRD分析表明,多层混合薄膜的衍射峰是PZT和PT两种薄膜衍射峰的叠加．     

PB/Au/CILE的制备与应用

混合离子液体(N-丁基吡啶六氟磷酸盐,[BuPy][PF6])与石墨粉,制备了离子液体碳糊电极(CILE),再采用电沉积法制得PB/Au/CILE修饰电极,研究了该修饰电极的电化学行为及其对H2O2的电催化,建立了H2O2的计时安培测定新方法。结果表明:在该修饰电极上PB产生了一对准可逆的氧化还原峰,并对H2O2表现出良好电催化作用,安培法测定H2O2的线性范围为5.0×10-6～1.55×10-4mol/L,检出限为1.0×10-6mol/L(S/N=3)。连续10次测定5.0×10-6mol/L H2O2峰电流的RSD为2.1%。     

Iron adsorption on SiO2/Si(111)

The adsorption of ferric and ferrous iron onto the native oxide of the SiO₂/Si(111) surface has been evaluated using X‐ray photoelectron spectroscopy (XPS). Through a series of immersion experiments, performed at room temperature and pH 1, it has been shown that the ferric species is strongly adsorbed onto the hydrophilic surface, while ferrous iron remains in solution. Dehydroxylation of the silica surface by etching with hydrofluoric acid reduces the concentration of receptive Si‐OH groups, thereby limiting iron adsorption. The experiments were reproduced in a combined ultrahigh vacuum‐electrochemical system (UHV‐EC), which allowed a carbon‐free surface to be prepared before contacting the iron solutions, and confirmed the strong affinity of ferric iron towards the SiO₂/Si(111) surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Fabrication of SiO2-TiO2/PVDF Copolymer Nanofiber Composite by Electrospinning Process

Multifunctional nanocomposite material is a key material component for the future. It is indicated by many studies have been conducted by researchers in university, research institute and industries. Silicon dioxide (SiO₂), titanium dioxide (TiO₂) and polyvinilidene fluoride copolymer are very important material due to their excellent properties. In this research paper, we have successfully synthesized SiO₂-TiO₂/PVDF copolymer nanofiber composite by electrospinning process. SiO₂-TiO₂/PVDF copolymer nanofiber composite has smooth surface morphology without bead on nanofiber string after confirming by scanning electron microscopy (SEM). Nanofiber composite has average diameter of 350 nm. FTIR and XRD structure analysis of nanofiber composite show us that PVDF copolymer in nanocomposite has a mixed α and β phase crystal structure. Crystal phase of TiO₂ in nanofiber composite was in rutile form.     

Biomimetic creation of hierarchical surface structures by combining colloidal self-assembly and Au sputter deposition

Surfaces of hexagonally packed silica spheres have been functionalized with silanes containing different hydrocarbon or fluorocarbon chains. The resulting chemical and physical structures were studied to establish the effect of surface hydrophobicity on the measured contact angles on the rough surfaces. The results were used to assess the effects of surface modifications on the parameters in the Cassie equation. To achieve superhydrophobicity via a biomimetic approach, we created two-scale structures by first forming hexagonally packed SiO2 spheres, followed by Au deposition on the spheres and heat treatment to form Au nanoparticles on sphere surfaces. Contact angles over 160 degrees were achieved. This work provides improved understanding of the effect of the surface roughness and solid surface fraction on superhydrophobicity.     

Oxygen-assisted reduction of Au species on Au/SiO2 catalyst in room temperature CO oxidation

An unexpected oxygen-assisted reduction of cationic Au species by CO was found on a Au/SiO(2) catalyst at room temperature and the produced metallic Au species plays an essential role in CO oxidation on Au/SiO(2).