An approach for fabricating self-assembled monolayer of Ag nanoparticles on gold as the SERS-active substrate

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol (p-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate.

DNA Extraction Using a Tetramethyl Orthosilicate-Grafted Photopolymerized Monolithic Solid Phase

A novel high-capacity, high-efficiency DNA extraction method is described using a photopolymerized silica-based monolithic column in a fused-silica capillary. Development involved investigation of the composition of the sol-gel monomer, fabrication conditions, and surface modifications in order to optimize the binding capacity. Extraction capacity and efficiency with the 3-(trimethoxysilyl)propyl methacrylate (TMSPM) monolith formulations fabricated in capillaries were investigated using a simple three-step procedure consisting of sample loading, washing of the solid phase, and elution of the DNA using a low ionic strength Tris buffer at pH 8. Once the TMSPM monomer concentration was optimized to yield a monolith with maximum test stability (robustness) and minimum back pressure, the monolith surface was modified by the grafting of tetramethyl orthosilicate (TMOS) for increased DNA binding capacity. After the examination of a variety of TMOS concentrations, 85% v/v TMOS was found to be optimal for DNA extraction without any obvious changes to the monolith structure. The reduction of time allowed for TMSPM hydrolysis prior to UV polymerization from 20 to 5 min led to a lower back pressure of the monolith, enabling better TMOS derivatization and therefore higher binding capacity. Minimal buffer volume (as low as 1 muL) was required to elute DNA from the solid phase, providing a DNA concentrating effect potentially important for downstream processes. While experimentation employed monolithic columns that were 12 cm in length, reduction of the length to 2 cm still allowed for a DNA binding capacity of at least 100 ng of prepurified human genomic DNA and extraction efficiencies greater than 85%. Extraction of low sample volumes (submicroliter) of human whole blood were successfully performed, with extraction efficiencies from the 2-cm monolithic column higher than those obtained from a commercial DNA extraction kit. These results position this novel matrix as an attractive alternative for solid-phase extraction of DNA and other biologically active molecules in microscale devices.

Highly photoluminescent multilayer QD-glass films prepared by LbL self-assembly

A novel and facile preparation method for layer-by-layer (LbL) self-assembled films incorporating quantum dots (QDs) and having intense photoluminescence (PL) from blue to red is presented. Functional sol-gel-derived glass layers prepared by the hydrolysis of 3-aminopropyltrimethoxysilane (APS) or 3-mercaptopropyltrimethoxysilane (MPS) have been used as a linkage between QD layers. Absorption, PL spectroscopy, transmission electron microscopy, and atomic force microscopy were employed for characterization, which revealed that the QDs in the prepared films had a nearly close-packed coverage and were not aggregated. The PL efficiencies of the QDs (CdTe or ZnSe, both are thioglycolic acid-stabilized) dispersed in the films were roughly half that of the initial colloidal solutions but reached 24% before a refractive index correction. The thickness of the red-emitting film with 10 CdTe QD layers was approximately 50 nm. The concentration of QDs in the film derived from the first absorption peak was approximately 0.01 M. Because the PL starts to show a red shift, the obtained concentration is practically the ultimate one in the glass matrix. The mercapto, amino, and carboxyl groups play important roles in LbL self-assembling processes.

Optimization of solid-phase microextraction conditions for the determination of triclosan and possible related compounds in water samples

A solid-phase microextraction (SPME) method for the determination of triclosan, methyl triclosan, 2,4-dichlorophenol and 2,3,4-trichlorophenol (considered as possible triclosan metabolites) in water samples was optimised. Analytes were first concentrated on a SPME fibre, directly exposed to the sample, and then triclosan and the two chlorinated phenols on-fibre silylated using N-methyl-N-(tert.-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Methyl triclosan remained unaffected during the derivatization step. Compounds were determined using gas chromatography in combination with mass spectrometry (GC-MS). Influence of different factors on the efficiency of extraction and derivatization steps was systematically investigated. Using a polyacrylate (PA) fibre quantification limits below 10 ng/l, and acceptable relative standard deviations, were obtained for all compounds after an extraction time of 30 min. On-fibre silylation was carried out in only 10 min. Moreover, the efficiency of the procedure was scarcely affected by the type of water sample. The method was applied to several samples of treated and raw wastewater, triclosan was found in all samples, at concentrations from 120 to 14,000 ng/l, and 2,4-dichlorophenol in most of them, at levels up to 2222 ng/l.

Core/Shell Particles Containing 3-(Methacryloxypropyl)-Trimethoxysilane in the Shell: Synthesis, Characterization, and Application

In comparison to the corresponding single-component counterparts, core/shell particles are widely used due to their better physical and chemical properties. The surface properties of core/shell particles evidently play an important role in the process of application. It is easy to deduce that surface properties mostly depend on the properties of the component in the shell. Therefore, desirable materials of shell are very significant for the study of composite materials, especially in core/shell field. It is well known that polysiloxane has excellent properties, such as the water repellency, high flexibility, low surface energy, and biocompatibility. Its application, however, is limited due to poor cohesiveness and poor film-forming properties. Recently, much endeavor has been made to overcome such flaws. It is found that polyacrylate is commonly considered for its good cohesiveness and excellent film-forming property. The combination of polysiloxane and polyacrylate has been shown to be important in the composite material field, especially as core/shell particles. Unfortunately, their hydrophobicity is considerably different and thus, the core/shell particles consisting of polyacrylate (PA)/polysiloxane (PSi) are hard to prepare by general seeded emulsion polymerization, and are also scarcely available in the literature. In this study, the new core/shell PA/PSi particles with poly(butyl methacrylate) (PA) as the core and poly(3-(methacryloxypropyl)-trimethoxysilane) (PSi) as the shell were prepared by dispersion polymerization under the kinetically controlled conditions. The characterization of the particles by TEM, DSC, particle size analyzer as well as static contact angle confirmed the formation of core/shell structure. The application of core/shell (PA/PSi) particles also has been considered and discussed here.TEM micrographs of core/shell (PA/PSi) particles.

Rapid and sensitive determination of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with on-line regenerating covalent coating

A rapid, sensitive and reproducible micellar electrokinetic chromatographic method using hexamethyldisilazane as on-line regenerating covalent coating was developed for the quantification of ephedrine (E) and pseudoephedrine (PE). E and PE were derivatized with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol for laser-induced fluorescence detection. The on-line regenerating covalent coating formed a combinative double coating with the subsequently produced dynamic SDS coating. The total coating can be easily removed and conveniently regenerated on-line. The simple coating procedure was described. By a series of optimization, a running buffer of 20 mm Na(2)B(4)O(7) + 16 mm SDS was applied for the separation of the derivatives. Linear relationships for E and PE were obtained in the range of 0.044-6.60 microg mL(-1) (correlation coefficients: 0.9975 for E, 0.9981 for PE), and the detection limits for E and PE were 1.71 and 0.67 ng mL(-1), respectively. The separation speed, the reproducibility and the sensitivity were much improved over those of other capillary electrophoresis methods more recently reported. The method was applied to the analysis of the two alkaloids in traditional herbal preparations with recoveries in the range 92.8-104.8%.

New application of air-drying techniques for studying Ephemeroptera and Plecoptera eggs by scanning electron microscopy

Hexamethyldisilizane (HMDS) and tetramethylsilane are organic compounds that are volatile at ambient temperature and which can therefore be used for air-drying biological samples for SEM studies. The techniques using these compounds provide results that are comparable with those obtained by critical point drying, but which involve a very simple process that saves time and money. Both techniques were applied to SEM studies of Ephemeroptera and Plecoptera eggs in order to assess their suitability as alternative methods to critical point drying for these kinds of biological material. The results show no morphological differences between eggs HMDS air-dried and critical point-dried.

Effectiveness of Bonding Systems on Bonding Durability of a Prefabricated Porcelain Material

The purpose of the present study was to evaluate the bond strength and durability of four bonding systems joined to a prefabricated porcelain material (Vita Celay Blanks). Two sizes of porcelain block were bonded with one of the following systems: (1) Clapearl Bonding Agent and Clapearl DC; (2) Imperva Porcelain Primer and Imperva Dual; (3) Monobond S and Variolink II; or (4) Tokuso Ceramics Primer and Bistite II. Shear bond strength was measured after 24-hour immersion in water and after subsequent thermocycling. The average pre- and post-thermocycling bond strengths in MPa (n=8) were: 52.5 and 42.5 for bonding system (1), 47.7 and 32.8 for (2), 55.0 and 48.8 for (3), and 51.5 and 25.6 for (4). Although prethermocycling results were not statistically different from each other, Group (3) exhibited the greatest strength after thermocycling.

Electrochemical impedance behavior of DNA biosensor based on colloidal Ag and bilayer two-dimensional sol-gel as matrices

A novel method for fabrication of DNA biosensors has been developed by means of self-assembling colloidal Ag (Ag) to a thiol-containing sol-gel network. The thiol groups of 3-mercaptopropyltrimethoxysilane (MPTS) serve as binding sites for the covalent attachment to gold electrode surface. Then the one-dimensional network of silane unites (1dMPTS) was combined together into a two-dimensional sol-gel network (2dMPTS) by dipping into aqueous NaOH. The second silane layer (B2dMPTS) was formed by immersing electrodes back into the MPTS solution overnight, and then the Ag nanoparticles were chemisorbed onto the thiol groups of the second silane layer. Finally, the mercapto oligonucleotide was self-assembled onto the surface via the Ag nanoparticles. The modified process was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). In addition, we utilized the impedance spectroscopy as a platform for DNA sensing assay. The factors influencing the performance of the resulting biosensor were studied in detail. The linear range of the biosensor was from 8.0 x 10(-9) to 1.0 x 10(-6) M with a detection limit of 4.0 x 10(-9) M at 3sigma. In addition, the experiment results indicate that oligonucleotide immobilized on this way exhibits a good sensitivity and selectivity, high stability and a long-term maintenance of bioactivity.

A multiresidue method for the analysis of phenols and nitrophenols in the atmosphere

A method using GC-MS and derivatization with N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) was developed for the analysis of 20 phenolic compounds in atmospheric samples (gas and particles). Air sampling was carried out using a Hi-Vol sampler with glass fibre filter and XAD-2 resin at a flow rate of 60 m(3) h(-1). The particle and gas phases were collected separately over a period of 4 h. Samples were Soxhlet extracted, evaporated to dryness under nitrogen and refilled with acetonitrile. 100 microl of these extracts were derivatized with 100 microl of MTBSTFA at 80 degrees C for 1 h under strong stirring. Phenolic compounds were injected into a GC-MS in splitless mode and quantified as their TBDMS derivatives in the SIM mode. Mass spectral analysis of the derivatives of the 20 compounds studied indicates that the spectra are highly specific showing an ion at [M - 57]+ which is useful for structure confirmation or analysis at low levels using selected ion monitoring. Quantification limits varied between 5 microg l(-1) and 10 microg l(-1) which correspond to 20 pg m(-3) and 40 pg m(-3) for 250 m(3) of air sampled. This method was successfully applied to atmospheric samples.

Synthesis of 2'-O-substituted ribonucleosides

An efficient synthesis of 2'-O-substituted ribonucleosides, including 2'-O-TBDMS and 2'-O-TOM protected as well as 2'-O-Me and 2'-O-allyl derivatives is presented. Di-t-butylsilylene group was employed for simultaneous protection of 3'- and 5'- hydroxyl functions of nucleoside on the first step. Subsequent silylation or alkylation of free 2'-OH followed by introduction of suitable protection on the base moiety and removal of cyclic silyl protection gave target compounds in a high yield.

A metal dispersed sol-gel biocomposite amperometric glucose biosensor

A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a copper dispersed sol-gel derived ceramic-graphite composite. The copper in the biocomposite offers excellent electrocatalytic activity towards the reduction (at -0.2 V) as well as oxidation (at +0.45 V) of hydrogen peroxide liberated in the enzymatic reaction enabling sensitive and selective determination of glucose. A linear response to glucose in the concentration range between 2.7 x 10(-5) to 4.0 x 10(-3) M with a correlation coefficient of 0.9987 and 4.0 x 10(-5) to 5.6 x 10(-3) M with a correlation coefficient of 0.9989 were observed with the electrocatalytic reduction and oxidation, respectively. Ascorbic acid and uric acid did not interfere with the glucose measurement during catalytic reduction at -0.2 V, a Nafion membrane was used to eliminate these interferences during the electrocatalytic oxidation at +0.45 V. The combination of copper catalysis and the promising feature of sol-gel biocomposite favor the sensitive and selective determination of glucose with improved analytical capabilities.

Alternative method of rapid drying vascular specimens for scanning electron microscopy

PURPOSE

To report the use of hexamethyldisilazane (HMDS) as an alternative to critical point drying for preparing stented canine peripheral vessels for scanning electron microscopy (SEM).

TECHNIQUE

Vascular specimens were fixed in 4% formaldehyde overnight, dehydrated in a graded ethanol series, followed by immersion in 100% hexamethyldisilazane. After air drying, the specimens were mounted on stainless steel stubs, coated with gold, and examined in the SEM. The electron micrographs were of high quality, showing the layers of the vascular wall and the incorporated stent covered by a neointimal layer. The micrographs were comparable to corresponding histological sections, but detailed endothelial patterns were more visible.

CONCLUSIONS

HMDS treatment and subsequent air drying provides good quality scanning electron micrographs that reveal both endothelial patterns and the layered architecture of stented vessels. The disadvantage of HMDS drying may be a shrinkage and distortion similar to other drying agents. Ease of handling, low cost, and a high rate of success are advantages that favor HMDS desiccation over other drying methods.

Ethene/norbornene copolymerization by [MeSi(3-(tert)BuCp) (N(tert)Bu)]TiCl2/MAO-catalyst

Ethene/norbornene copolymerization by the catalyst system [Me2Si(3-(tert)BuCp) (N(tertBu)]TiCl2/ MAO was investigated in detail at 30 degrees C, 60 degrees C, and 90 degrees C. A mass flow controller was used in this work to obtain kinetic data and investigate temperature's effects on activity, norbornene incorporation, copolymerization parameter, microstructure, glass transition temperature, and molar masses were described. High copolymerization values r(E) and high alternation are determined. The number of isotactic alternating sequences is much higher than that of the syndiotactic alternating sequences.

Electrophysiological response of cultured trabecular meshwork cells to synthetic ion channels

The response of living cells of the trabecular meshwork to synthetic ion channels is described. The THF-gramicidin hybrids THF-gram and THF-gram-TBDPS as well as a linked gA-TBDPS and gramicidin A were applied to cultured ocular trabecular meshwork cells. THF-gram application (minimal concentration, 10(-8) M; saturation, 10(-7) M) led to an additional conductance which displayed characteristics of weak Eisenman-I-selective cation channels, no cell destruction, an asymmetric change of the inward/outward currents, and higher current densities using Cs(+) as charge carrier compared to Na(+) and K(+). Linked-gA-TBDPS showed at 10(-12) M increases of the membrane conductance comparable to gA at 10(-7) M and a much faster response of the cells. Thus, THF-gramicidin hybrids form a basis for the use of synthetic ion channels in biological systems, which eventually may lead to new therapeutic approaches.

Comparison of hexamethyldisilazane and critical point drying treatments for SEM analysis of anaerobic biofilms and granular sludge

We present a fast procedure for scanning electron microscopy (SEM) analysis in which hexamethyldisilazane (HMDS) solvent, instead of the critical point drying, is used to remove liquids from a microbiological specimen. The results indicate that the HMDS solvent is suitable for drying samples of anaerobic cells for examination by SEM and does not cause cell structure disruption.

Direct patterning of modified oligonucleotides on metals and insulators by dip-pen nanolithography

The use of direct-write dip-pen nanolithography (DPN) to generate covalently anchored, nanoscale patterns of oligonucleotides on both metallic and insulating substrates is described. Modification of DNA with hexanethiol groups allowed patterning on gold, and oligonucleotides bearing 5'-terminal acrylamide groups could be patterned on derivatized silica. Feature sizes ranging from many micrometers to less than 100 nanometers were achieved, and the resulting patterns exhibited the sequence-specific binding properties of the DNA from which they were composed. The patterns can be used to direct the assembly of individual oligonucleotide-modified particles on a surface, and the deposition of multiple DNA sequences in a single array is demonstrated.

Organo-silica nano-particles used in ultrahigh-pressure liquid chromatography

A simple one-step process was used to synthesize uniform, spherical organosilica nano-particles containing octadecyl moieties. These nano-particles, having a diameter of 670 nm, were slurry packed into fused-silica capillary tubes of 50 microm internal diameter and tested for use in ultrahigh-pressure liquid chromatography (UHPLC) at inlet pressures of about 50,000 psi (approximately 3,500 bar), providing for the use of HPLC with nano-particle packed columns. The retention characteristics of a column packed with the organo-nano-particles were shown to be stable under acidic (pH < 1) and basic (pH > 11) conditions. Fast analysis times and relatively high separation efficiencies (approximately 500,000 plates m(-1)) were obtained under the conditions used.

Surface passivation of a microfluidic device to glial cell adhesion: a comparison of hydrophobic and hydrophilic SAM coatings

Cell adhesion in a microfluidic structure can lead to catastrophic flow problems due to the comparable size of the cell with the microfabricated device. Such issues are important in the growing research area involving the merging of biological materials and MEMS devices. We have examined the surface compatibility of uncoated and coated microfabricated glass and semiconductor surfaces under static solution (cell culture) and flow experiments (microfluidic device) using glial (astrocyte and glioblastoma) cells. Bare semiconductor and glass surfaces were most attractive to cell adhesion, promoting biofouling under both static and flow conditions. Passivation of the surfaces was performed with silane coupling agents octadecyltrimethoxysilane (OTMS) or N-(triethoxysilylpropyl)-O-polyethylene oxide urethane (TESP) on SiO2 surfaces via self-assembled monolayer (SAM) deposition. The hydrophilic TESP coating was effective at inhibiting biofouling of the microfluidic structure, allowing greater than several minutes of fluid flow. The hydrophobic OTMS coating, on the other hand, promoted cell adhesion leading to restricted flow within a few minutes. Interestingly, under cell culture conditions the TESP surface exhibited biocompatible properties for glial cell adhesion and proliferation, in contrast to the OTMS surface which resisted cell growth. These studies suggest that cell adhesion is dependent upon the time domain of the cell-surface interaction.

[Preparation and chromatographic characteristics of octadecyl bonded titania stationary phase for high performance liquid chromatography]

Porous titania microspheres (surface area: 36.7 m2/g, average pore volume: 0.30 mL/g, average pore diameter: 32.2 nm, average diameter: 3.5 microns) with a very narrow particle size distribution, were synthesized by refluxing polymerized-induced colloid aggregation (PICA), with octadecyltrimethoxysilane in toluene as a solvent for 8 h, and octadecyltitania stationary phase (ODT) was obtained. The carbon content and hydrophobic selectivity of the stationary phase were 2.87% (i.e. 0.66 mumol/m2) and 0.4638, respectively. ODT showed good chromatographic performances when it was used to separate the neutral and basic solutes using methanol solution as a mobile phase.

Surface modification of stainless steel by grafting of poly(ethylene glycol) for reduction in protein adsorption

The surface of stainless steel was first modified by the silane coupling agent (SCA), (3-mercaptopropyl)trimethoxysilane. The silanized stainless-steel surface (SCA-SS surface) was subsequently activated by argon plasma and then subjected to UV-induced graft polymerization of poly(ethylene glycol)methacrylate (PEGMA). The chemical structures and composition of the pristine, silane-treated, plasma-treated and PEGMA graft-polymerized stainless-steel coupon surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The graft polymerization of PEGMA onto the plasma-pretreated SCA-SS surface was studied with different argon plasma pretreatment time, macromonomer concentration, and UV graft polymerization time. In general, a brief plasma pretreatment, high PEGMA concentration, and long UV graft polymerization time readily resulted in a high graft concentration. The PEGMA graft-polymerized stainless-steel coupon (PEGMA-g-SCA-SS) with a high graft concentration, and thus a high PEG content, was found to be very effective in preventing bovine serum albumin and gamma-globulin adsorption.