Diffusion of self-assembled monolayers of thiols on the gold surfaces covered with polydimethylsiloxane stamps

Thiols can diffuse and form self-assembled monolayers (SAMs) on the gold surfaces covered with polydimethylsiloxane (PDMS) stamps. For the first time, with cells as the indicator of how far alkanethiols had diffused to form SAM, we studied the growth dynamics of SAMs of HS(CH₂)₁₁(OCH₂CH₂)₃OH (EG₃) and HS(CH₂)₁₁(OCH₂CH₂)₆OH (EG₆) on the gold surfaces covered with PDMS stamps. The growth of SAMs is well described by one-dimensional diffusion from a line source of concentration, with surface diffusion coefficient of 193.4 ± 19.2 μm²/min (EG₃) and 95.8 ± 18.9 μm²/min (EG₆).     

Elastic properties of thin poly(vinyl alcohol)-cellulose nanocrystal membranes

In spite of extensive studies on the preparation and characterization of nanocomposite materials, the correlation of their properties at the nanoscale with those in bulk is a relatively unexplored area. This is of great importance, especially for materials with potential biomedical applications, where surface properties are as important in determining their applicability as bulk characteristics. In this study, the nanomechanical characteristics of thin poly(vinyl alcohol) (PVOH)-poly(acrylic acid) (PAA)-cellulose nanocrystal (CNC) membranes were studied using the nanoindentation module in an atomic force microscope (AFM) and the properties were compared with the macro-scale properties obtained by tensile tests. In general, the elastic properties measured by nanoindentation followed the same trend as macro-scale tensile tests except for the PVOH 85-PAA 0-CNC 15 sample. In comparison to the macro-scale elastic properties, the measured elastic moduli with AFM were higher. Macro-scale tensile test results indicated that, in the presence of PAA, incorporation of CNCs up to 20?wt% improved the elastic modulus of PVOH, but when no PAA was added, increasing the CNC content above 10?wt% resulted in their agglomeration and degradation in mechanical properties of PVOH. The discrepancy between macro-scale tensile tests and nanoindentation in the PVOH 85-PAA 0-CNC 15 sample was correlated to the high degree of inhomogeneity of CNC dispersion in the matrix. It was found that the composites reinforced with cellulose nanocrystals had smaller indentation imprints and the pile-up effect increased with the increase of cellulose nanocrystal content.     

Micro- and nanostripes of self-assembled Au nanocrystal superlattices by direct micromolding

A simple, inexpensive direct micromolding method for patterning Au nanocrystal superlattices using a polydimethylsiloxane (PDMS) stamp has been developed. The method involves in situ synthesis of Au(I) dodecanethiolate and its decomposition leading to Au nanocrystals in the microchannels of the stamp which order themselves to form patterned superlattice stripes, in conformity with the stamp geometry. Owing to its insolubility in common solvents, the dodecanethiolate was made by reacting Au(PPh₃)Cl and dodecanethiol in situ inside the microchannels, by injecting first the former solution in toluene at room temperature followed by the thiol solution at 120 °C. Annealing the reaction mixture at 250 °C, resulted in formation of nanocrystals (with a mean diameter of 7.5 nm) and hexagonal ordering. By using an external pressure while molding, parallel stripes with sub-100 nm widths were obtained. The choice of parameters such as injection temperature of the thiol and concentrations is shown to be important if an ordered superlattice is to be obtained. In addition, these parameters can be varied as a means to control the nanocrystal size.     

Fabrication and characterization of self-assembled spherical gold ultramicroelectrodes

Spherical ultramicroelectrodes with diameters of 1-30 μm have been prepared by self-assembly of Au nanoparticles and 1,9-nonanedithiol molecules at the tip end of glass micropipets. The electrodes were characterized by optical and scanning electron microscopy, cyclic voltammetry in aqueous and acetonitrile solution, and scanning electrochemical microscopy approach curves. A modified theory for hemispherical electrodes was used to compute the approach curves, which agreed with the experimental results. The construction strategy represents a bottom-up approach to the fabrication of microspherical electrodes.     

Composite fluoroplastic fibrous filtration membranes

New fibrous materials and related composite membranes have been obtained using fluoroplastic copolymer fibers produced by means of electrospinning. The composite membranes comprise alternating layers of fine and coarse fibers performing different functions: thin fibers determine the filtration properties, while thick fibers provide the necessary mechanical strength.     

Electrochemical properties of self-assembled cytochrome c on gold substrate patterned with a photosensitive polyimide film

Photosensitive polyimide having benzene and sulfonyloxyimide moieties was prepared and microarray pattern on gold substrate was obtained by a UV lithographic technique. The well-characterized monolayer of cytochrome c was immobilized on the patterned gold substrate by self-assembly process. The bioelectrochemical activity between cytochrome c molecular center and electrode interface for the self-assembled cytochrome c monolayer was investigated through the measurement of cyclic voltammetry. The integration and morphology of cytochrome c molecule through the measurement of AFM was also examined.     

Effect of thiol chemisorption on the transport properties of gold nanotubule membranes

An electroless gold deposition method was used to deposit Au nanotubules within the pores of a polycarbonate template membrane. Membranes containing Au nanotubules with inside diameters of 2 and 3 nm were prepared for these studies. Thiols were chemisorbed to the inside tubule walls in order to change the chemical environment within the tubules. The effect of the chemical environment within the tubules on the transport properties of the tubule-containing membrane was investigated. Membranes modified with HS-C(16)H(33) preferentially transported hydrophobic permeant molecules. When a homologous series of permeant molecules was used, the most hydrophobic permeant was preferentially partitioned into and transported by the HS-C(16)H(33) derivatized membrane. In addition, the effect of alkyl chain length (R), in a homologous series of thiols R-SH, was investigated. Hydrophobic permeant molecules were preferentially partitioned into and transported by membranes containing the largest alkyl group. In contrast, membranes modified with HS-C(2)H(4)OH preferentially transported the more hydrophilic permeant pyridine. Finally, we show here that the HS-C(16)H(33) derivatized membrane can be used to separate hydrophobic species from hydrophilic species.     

Negative supracrystals inducing a FCC-BCC transition in gold nanocrystal superlattices

The growth of nanocrystal superlattices of 5 nm single domain Au nanocrystals at an air-toluene interface induces formation of well-defined thin films （300--400 nm） with large coherence lengths. High-resolution electron microscopy showed that polyhedral holes （negative supracrystal） were formed on the nanocrystal superlattice surface. Formation of negative supracrystals is attributed to inclusion in the superlattice of organic molecules （dodecanethiol）, which are present in concentrated zones at the air-toluene interface. The coexistence of two supracrystalline structures （bcc/fcc） is attributed to diffusion of dodecanethiol molecules resulting in a Bain deformation of the nanocrystal array.     

Adsorption characteristics of self-assembled thiol and dithiol layer on gold

Monolayers of functional proteins are important in many fields related to pure and applied biochemistry and biophysics. The formation of extended uniform protein monolayers by single- or multiple-step self-chemisorption depends on the quality of the functionalized gold surface. The optical and the electrical properties of the 1-nonanethiol and 1,9-nonanedithiol deposited on gold with the self-assembled technique were investigated. We use cyclic voltammetry and impedance spectroscopy to characterize the insulating properties of the two layers. The analysis of the impedance spectra in terms of equivalent circuit of the gold/electrolyte and gold/SAM/electrolyte interface allows defining the thickness of the two thiols and the percentage of coverage area. Atomic force microscopy, contact angle measurement and Fourier transform infra-red spectroscopy have been used for homogeneity, hydrophobic properties and molecular structure of the formed thiols layer, respectively. The measured thickness with impedance spectroscopy fit well the results found with atomic force microscopy.     

掺铁TiO2纳米晶的制备及光催化性能研究

以钛酸丁酯溶液为前驱体，采用溶胶-凝胶法制备了不同掺杂量的Fe^3 -TiO2干凝胶，在空气气氛中于400℃焙烧2h，得到锐钛矿相的纳米晶，用TG-DTA，XRD，DRS，FS等手段对其进行了表征，研究结果表明，掺杂铁离子使二氧化钛纳米晶的粒径变小，吸收带边发生红移，荧光峰明显增强，分别以汞灯和氙灯为光源，通过对染料罗丹明B的光催化降解研究，发现掺入0.01?^3 -TiO2与纯TiO2相比具有更好的催化活性，掺杂量增大后，光催化降解率反而下降。     

Diffusion bonding of pd-ag rolled membranes

Cold-rolled and annealed Pd-Ag 25% at. foils of thickness 50 m have been joined by diffusion bonding in order to obtain permeator tubes used in laboratory applications for hydrogen separation and purification. The tubes produced present a sound and effective joint along the generatrix line: particularly, this procedure has shown better performance than arc welding, responsible for formation of thermally stressed zones and embrittlement of permeators.Based on the high diffusion of the Ag atoms, the joining procedure of the tubes consists of a thermal treatment at 1100°C for 1 h under controlled atmosphere (Ar-H 5%), where the overlapped limbs of the metal foil have been compressed in a special device.This joint obtained by diffusion bonding has shown absence of defects and good chemical and physical stability after thermal and hydrogenation cycling of the permeator tubes under their operating conditions. Characterization tests carried out in the temperature range 300–400°C on these membrane tubes have given hydrogen permeability values according to the literature.     

Nanoporous aluminum oxide membranes for filtration and biofunctionalization

Nanoporous aluminum oxide membranes with high open porosity are prepared by anodic oxidation. Conventional self-supporting as well as mechanically stabilized nanoporous membranes are produced from aluminum plates and microimprinted aluminum foils, respectively. The mechanically stabilized membranes are characterized by very thin membrane parts stabilized by surrounding thick bridges. The minimal thickness of these thin membranes with open pores on both sides is 1 microm, with a mean pore size of the parallel open pores of 185 nm. With these two kinds of membrane the flow rates for cross filtration can be tuned over a wide range. With the mechanically stabilized membranes, substantially higher flow rates are achieved and experiments that cannot be performed with thicker membranes become possible. The biofunctionalization of the pore walls with archaebacterial tetraether lipids is realized and proved using aminated semiconductor nanocrystals. The lipid layer deposited on the pore walls also changes the filtration properties.     

Diffusion characteristics of mixed-cation ion-exchange membranes

Approaches are proposed for determining diffusion parameters of mixed-cation membranes. One of them is used to evaluate diffusion coefficients and effective ion-exchange constants in membranes containing both H⁺ and M⁺ (M = Li, Na, K, Rb) cations from ionic conductance and interdiffusion data for samples in equilibrium with solutions differing in the ratio of salt and acid concentrations.     

Surface-enhanced Raman scattering of dopamine on self-assembled gold nanoparticles

Dopamine, a potent neurotransmitter in the brain, influences a variety of motivated behaviors and plays a major role in Parkinson's disease. In this study, the Raman signal of dopamine was detected on a fabricated nanoparticle-immobilized glass surface by surface-enhanced raman spectroscopy (SERS). Amine-modified glass was prepared by the self-assembly of amine-terminated silane on substrate, followed by the deposition of gold nanoparticles. The gold nanoparticles deposited on the glass surface were functionalized by anti-dopamine or dopamine. The antigen-dopamine was captured by antibody-assembled gold substrate and detected by SERS. The optical properties and morpology of the glass substrate with immobilized gold nanoparticles were analyzed by scanning electron microscopy and UV-VIS absorption spectroscopy. The Raman spectrum of dopamine displayed broad bands at 1267, 1331, 1158, 1478, 1578 and 1584 cm(-1). The strongest peaks in the spectra (at 1267 and 1478 cm(-1)) were identified as phenolic carbon-oxygen and phenyl C=C stretches, respectively. A working curve of the SERS signal constructed from cathecol ring vibration versus antigen-dopamine concentration was obtained at 1478 cm(-1), and the non-optimized detection limit for anti-dopamine surface antigen was as low as 1 ng/ml. These results suggest that SERS-based immunosensor can be a promising tool for the detection and screening of neurotransmitters.     

Effect of PbS nanocrystal concentration on the physical properties of a polymer–nanocrystal composite

Semiconductor nanocrystals doped in stable matrices such as polymers are of interest due to fundamental scientific aspects as well as their scope for technological applications. In the present investigation, PbS nanocrystals are synthesized in polyvinyl alcohol (PVA) matrix using a simple technique based on colloidal chemistry. Various concentrations of nanocrystalline PbS (with an average size of 4.5 nm) are loaded into the polymer to study the effect of PbS concentration on the optical, thermal and electrical properties of the composite. An increase in PbS content results in decrease in thermal stability and an increase in electrical conductivity, presumably resulting from interactions between the nanofiller and polymer. Considerations for designing composites with desired combinations of electrical, thermal, and optical properties to suit specific device operating environments are studied systematically.     

Selective gold deposition via CVD onto self-assembled organic monolayers

We demonstrate a selective deposition of ultrathin gold layers via CVD onto self-assembled dithiols. Dithiols have been self-assembled to produce a thiolated surface. Metallic gold was deposited from the gas phase by using a volatile organometallic molecular gold precursor. The gold layer is bound to the exposed thiol groups. We demonstrate a selective deposition of the gold only at the areas where the binding thiol groups are located and characterized the deposition process and the obtained coatings with spontaneous desorption time of flight mass spectrometry and Rutherford backscattering spectroscopy.     

Immobilisation of cobaltferritin onto gold electrode based on self-assembled monolayers

The iron storage protein, ferritin, has a cavity of ～7?nm in diameter in which iron is oxidised and stored as a hydrated oxide core. Electron transfer is known to be an important step in the sequestering of iron by cellular ferritin. The cavity was used as a nanocontainer to grow cobalt nanoparticles. The immobilisation of ferritin on the electrode surface is essential for various bioelectronic applications. A cobaltferritin-immobilised electrode based on self-assembled monolayer (SAM)-modified gold electrode was developed. The cobaltferritin-immobilised SAM-modified electrode was characterised by electrochemical and atomic force microscopy (AFM) techniques. The results indicated that cobaltferritin was selectively immobilised onto succinimidyl alkanedisulfide-modified Au electrode by the covalent interaction between cobaltferritin and the terminal functional groups of the SAMs. The cobaltferritin immobilised modified electrode showed a direct electron transfer reaction between cobaltferritin and the electrode. The electrochemically regulated uptake and release of cobalts for cobaltferritin immobilised on the SAMs were demonstrated. The results obtained in this study indicate that cobaltferritin has potential for a biomaterial in nanoscale synthesis for potential magnetic, catalytic and biomedical-sensing applications.     

Immobilization of methylene blue on self-assembled iodine monolayers on gold

The immobilization of methylene blue (MB) on iodine-covered Au(111) is studied by electrochemical techniques, scanning tunneling microscopy (STM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. Results show that MB species are efficiently adsorbed on the square root of 3 x square root of 3 R30 degrees I lattice on Au(111). The electrochemical behavior of the adsorbed MB molecules is reversible, indicating a relatively fast electron transfer from the Au(111) surface to the immobilized MB species through the iodine layer. STM images with molecular resolution are consistent with adsorption of MB dimers on a square root of 3 x square root of 3 R30 degrees I lattice placed atop of the Au(111) substrate. Results are compared to those obtained for MB immobilized on Au(111) covered by S(n) (n = 3-8) surface structures.