Vapor-liquid-solid grown silica nanowire based electrochemical glucose biosensor

Vapor-liquid-solid (VLS) grown silica nanowires (SiO(2)NWs) have been deposited electrophoretically on a gold electrode and utilized for covalent immobilization of glucose oxidase (GOx). Covalent binding has been achieved via 3-aminopropyltriethoxysilane (APTES) modification and N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide chemistry. Scanning electron microscopy, transmission electron microscopy and cyclic voltammetry techniques have been used to characterize SiO(2)NW and GOx/APTES/SiO(2)NW/Au bioelectrode. Electrochemical studies reveal that SiO(2)NW increases the effective electro-active surface area thus resulting in higher loading of enzyme. Response characteristics show linearity in the range of interest 25-300 mg dl(-1), with a detection limit of 11 mg dl(-1), sensitivity: 0.463 μA (mg dl(-1))(-1) and regression coefficient of 0.992.     

Nisin antimicrobial activity and structural characteristics at hydrophobic surfaces coated with the PEO-PPO-PEO triblock surfactant Pluronic F108

The antimicrobial peptide nisin has been observed to preferentially locate at surfaces coated with the poly[ethylene oxide]-poly[propylene oxide]-poly[ethylene oxide] (PEO-PPO-PEO) surfactant Pluronic F108, to an extent similar to its adsorption at uncoated, hydrophobic surfaces. In order to evaluate nisin function following its adsorption to surfaces presenting pendant PEO chains, the antimicrobial activity of nisin-loaded, F108-coated polystyrene microspheres and F108-coated polyurethane catheter segments was evaluated against the Gram-positive indicator strain, Pediococcus pentosaceus. The retained biological activity of these nisin-loaded layers was evaluated after incubation in the presence and absence of blood proteins, for contact periods up to one week. While an increase in serum protein concentration reduced the retained activity on both bare hydrophobic and F108-coated materials, F108-coated surfaces retained more antimicrobial activity than the uncoated surfaces. Circular dichroism spectroscopy experiments conducted with nisin in the presence of F108-coated and uncoated, silanized silica nanoparticles suggested that nisin experienced conformational rearrangement at a greater rate and to a greater extent on bare hydrophobic surfaces relative to F108-coated surfaces. These results support the notion that immobilized, pendant PEO chains confer some degree of conformational stability to nisin while also inhibiting its exchange by blood proteins.     

Separation of somatropin charge variants by multiple‐injection CZE with Polybrene/chondroitin sulfate A double‐coated capillaries

The performance of dynamic double‐coated fused‐silica capillaries with Polybrene and chondroitin sulfate A has been compared with uncoated fused‐silica capillaries for the determination of recombinant human growth factor (somatropin) charge variants. The separations were carried out under the same electrophoretic conditions as described in the European Pharmacopoeia, i.e. at pH 6.0 and 30°C. The coating significantly reduced the interactions between the proteins and the surface of the fused‐silica capillary. The first five separations performed in a new bare fused‐silica capillary were discarded because of very poor separation performance as a result of protein–surface interactions. There was an approximate twofold increase in the interday migration time precision (%RSD ≤ 6.5%) in the double‐coated capillaries. The method was successfully transferred to a multiple CZE mode where two samples were analyzed in a single electrophoretic run. The average purity of somatropin certified reference standard was 98.0% (%RSD ≤ 0.3%) determined by using uncoated and coated capillaries.     

Ag-SiO2 core-shell nanorod arrays: morphological, optical, SERS, and wetting properties

Using the hydrolysis of tetraethylorthosilicate, a uniform and conformal layer of porous SiO(2) with controlled thickness has been coated onto the oblique angle deposited Ag nanorod (AgNR) array to form an aligned AgNR-SiO(2) core-shell array nanostructure. The morphology, optical property, SERS response, and surface wettability of the AgNRs with different SiO(2) shell thicknesses have been obtained by multiple characterization techniques. The morphological characterization shows that each AgNR on the array is coated with a uniform and porous silica shell independently and the growth of shell thickness follows a linear function versus the coating time. Thickening of the shell induces a monotonic decrease of the apparent contact angle, red-shift of the transverse mode of the localized surface plasmon resonance peak, and makes the SiO(2) shell more compact. The SERS response of 4-Mercaptophenol on these substrates exhibits an exponential decay behavior with the increasing coating time, which is ascribed to the decreasing Ag surface coverage of core-shell nanorods. Under the assumption that the Ag surface coverage is proportional to the SERS intensity, one can estimate the evolution of SiO(2) coverage on AgNRs. Such coverage evolution can be used to qualitatively explain the LSPR wavelength change and quantitatively interpret the contact angle change based on a double Cassie's law.     

Nisin adsorption to hydrophobic surfaces coated with the PEO-PPO-PEO triblock surfactant Pluronic F108

The adsorption and elution of the antimicrobial peptide nisin at hydrophobic, silanized silica surfaces coated with the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) surfactant Pluronic F108 were measured in situ, with ellipsometry. While such layers are known to inhibit protein adsorption, nisin was observed to adsorb in multilayer quantities, to an extent similar to its adsorption at uncoated, hydrophobic surfaces. The rates of nisin adsorption and elution were generally slower at F108-coated surfaces. And, the sequential adsorption of nisin, including two adsorption-elution cycles at each surface, showed greater differences in adsorption rates between the first and second adsorption cycles, when evaluated at identical mass density, for uncoated relative to F108-coated surfaces. These results indicate that nisin adsorption occurs via "entrapment" within the PEO brush layer at F108-coated surfaces, in this way slowing adsorption and spontaneous elution, and inhibiting post-adsorptive molecular rearrangements by reducing the lateral mobility of nisin. While F108-coated layers rejected adsorption of serum albumin, sequential adsorption experiments carried out with nisin and albumin showed a low level of albumin adsorption when nisin was present at the interface.     

The structural and electronic properties of Ag-adsorbed (SiO2)n (n=1-7) clusters

Equilibrium geometries, charge distributions, stabilities, and electronic properties of the Ag-adsorbed (SiO(2))(n) (n=1-7) clusters have been investigated using density functional theory with generalized gradient approximation for exchange-correlation functional. The results show that the Ag atom preferably binds to silicon atom with dangling bond in nearly a fixed direction, and the incoming Ag atoms tend to cluster on the existing Ag cluster leading to the formation of Ag islands. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of the silica clusters is minor, attributing to the tendency of stability order of Ag(SiO(2))(n) (n=1-7) clusters in consistent with silica clusters. In addition, the energy gaps between the highest occupied and lowest unoccupied molecular orbitals remarkably decrease compared with the pure (SiO(2))(n) (n=1-7) clusters, eventually approaching the near infrared radiation region. This suggests that these small clusters may be an alternative material which has a similar functionality in treating cancer to the large gold-coated silica nanoshells and the small Au(3)(SiO(2))(3) cluster.     

Highly luminescent CdSe/Cd(x)Zn(1-x)S quantum dots coated with thickness-controlled SiO2 shell through silanization

A silanization technique of hydrophobic quantum dots (QDs) was applied to SiO(2)-coated CdSe/Cd(x)Zn(1-x)S QDs to precisely control the SiO(2) shell thickness and retain the original high photoluminescence (PL) properties of the QDs. Hydrophobic CdSe/Cd(x)Zn(1-x)S core-shell QDs with PL peak wavelengths of 600 and 652 nm were prepared by a facile organic route by using oleic acid (OA) as a capping agent. The QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate by replacing surface OA. These silanized QDs were subsequently encapsulated in a SiO(2) shell by a reverse micelles synthesis. The silanization plays an important role for the QDs to be coated with a homogeneous SiO(2) shell and retain a high PL efficiency in water. Transmission electron microscopy observation shows that the shells are 1-9 nm with final particle sizes of 10-25 nm, depending on the initial QD size. In the case of short reaction time (6 h), the QDs were coated with a very thin SiO(2) layer because no visible SiO(2) shell was observed but transferred into the water phase. The silica coating does not change the PL peak wavelength of the QDs. The full width at half-maximum of PL was decreased 4 nm after coating for QDs emitting at both 600 and 652 nm. The PL efficiency of the SiO(2)-coated is up to 40%, mainly determined by the initial PL efficiency of the underlying CdSe/Cd(x)Zn(1-x)S QDs.     

Fabrication of NiO coated SiO2 and SiO2 coated NiO for the removal of Pb2＋ ions

We have prepared silica,SiO2coated NiO and NiO coated SiO2by sol-gel method.The physicochemical properties of the desired materials were investigated by surface charge properties,scanning electron microscopy（SEM）,energy dispersive X-ray（EDX） spectroscopy,surface area measurements and X-ray diffraction（XRD） analyses.The point of zero charge（PZC） of the solid was determined by the salt addition method.In coated materials,two PZC values were noted representing the surface charge of their counterparts.The SEM image of SiO2coated NiO displays a uniform coating of silica on the surface of NiO whereas in case of NiO coated SiO2,a honeycomb like appearance was observed with highly porous structures.In the diffractograms of NiO,the characteristic peaks were suppressed in NiO coated silica however,no diffraction peak could be seen in SiO2coated NiO.Batch adsorption technique was applied for the removal of Pb2＋ions from aqueous solution.The sorption trend for Pb2＋ions was observed in the order of NiO coated SiO2〉 SiO2coated NiO 〉 NiO 〉 SiO2.This trend confirms that the coated materials have more sorption capacities than their parent counterparts.     

Gas chromatographic retention in uncoated fused silica capillaries

Understanding of retention in uncoated fused‐silica capillaries is of interest due to increased attention on precolumn backflushing in capillary GC. Uncoated capillaries offer several advantages as precolumns compared to coated precolumns. In order to examine the possibility of predicting elution temperatures of alkanes from uncoated capillaries a priori, several sizes of deactivated but uncoated fused‐silica capillaries were evaluated under various operating conditions. Retention was found to depend on dimensionless ramp rate (°C/t_M), sample loading (capacity), flow mode, and column dimensions (probably related to surface area).     

Silane-based poly(ethylene glycol) as a primer for surface modification of nonhydrolytically synthesized nanoparticles using the Stöber method

This paper describes the use of methoxy-poly(ethylene glycol) silane (MPEG-sil) as a linker molecule for the synthesis of silica-coated nanoparticles by the St?ber method. While short alkane chain-based siloxanes including (acryloxypropyl)trimethoxysilane and 3-methacryloxypropyl-trimethoxysilane are popular molecules used in surface modification, they are not efficient for the silica coating of nanoparticles synthesized from organic solvents containing long carbon chain carboxylic acids or amines as capping agents. Here, we report the utilization of MPEG-sil to bridge this gap. Our approach is based on a two-phase system, in which ligand exchange takes place in a hydrophobic environment and the surface modification with silica is conducted in an ethanol-water mixture. Our results show that this two-phased approach was effective to coat monodisperse Fe2O3 nanoparticles capped with oleic acid and Ag nanoparticles capped with oleylamine with uniform SiO2 shells. The process was also demonstrated for double-shell nanostructures to produce SiO2-coated Pt@Fe2O3 core-shell nanoparticles. The results described in this work represent a new approach for the surface modification with silica coating of monodisperse nanoparticles synthesized from nonhydrolytic solutions and can potentially have a broad ramification in the development of water-dispersible nanoparticles for biological applications.     

Synthesis and antibacterial property of hollow SiO2/Ag nanocomposite spheres

This paper presents a novel and facile method to fabricate hollow silica/sliver (SiO(2)/Ag) nanocomposite spheres. In this approach, the monodisperse hollow SiO(2) colloids bearing quantenary ammonium groups were prepared by dispersion polymerization combined sol-gel process and used as templates. The Ag(+) ions were first adsorbed onto the surfaces of the hollow SiO(2) beads via electrostatic interaction and then in situ reduced by the deprotonated silanol groups of the hollow SiO(2) beads, no extra reducing agents or catalysts were added during the reduction process. TEM, SEM and EDX analyses indicated that Ag nanoparticles were successfully deposited onto the surfaces of hollow SiO(2) beads. Some influencing parameters, such as the amount of quantenary ammonium groups in the inner wall of hollow SiO(2) colloids, Ag(+) ions concentration and reaction temperature, on the deposition of Ag nanoparticles onto SiO(2) colloids were investigated. Preliminary antibacterial tests indicated that these hollow nanocomposite spheres showed excellent antibacterial ability.     

Microwave-assisted effi cient synthesis of azlactone derivatives using 2-aminopyridine-functionalized sphere SiO2 nanoparticles as a reusable heterogeneous catalyst

In the present work, the highly efficient Erlenmeyer synthesis of azlactones catalyzed by 2- aminopyridine, supported on nano-sphere SiO2 is reported. First, the silica nanoparticles were modified with triethoxysilylpropyl chloride and then 2-aminopyridine was attached to the support via covalent linkages. This new heterogenized catalyst was used for efficient microwave-assisted synthesis of azlactone derivatives with Ac2O as a condensing agent under solvent-free conditions. The present method offers advantages including high yields, short reaction times and simple work-up. Also, the catalyst can be easily recycled and reused several times, which makes this method attractive, economic and environmentally-benign.     

Effects of organic-inorganic hybrid coatings on durability of cross-linked polyethylene

Cross-linked polyethylene (XLPE) films have been coated with nanostructured hybrid organic-inorganic coatings in order to improve their durability. For this purpose, bi- and mono-layer coatings containing different amount of silica and different organic polymers have been prepared through sol-gel reactions and applied to XLPE commercial films. The thermo-oxidative stability, electrical strength and conductivity of XLPE coated films have been investigated after ageing in air at temperatures above the on-service conditions, i.e. at 105 and 120 °C for 1900 and 600 h, respectively. The performed investigations (FT-IR, DSC, TGA and electrical properties) showed that all the coatings tested were able to strongly protect XLPE against oxidation, and that the coating with a PVOH/SiO₂ layer gave the best protection. The increase of thermal resistance induced by the coatings reflects on the electrical strength after ageing, which is higher for coated samples than for uncoated ones. Moreover, while ageing has only a slight effect on electrical conductivity in different coated samples, a strong increase of conductivity was observed after ageing for highly oxidated uncoated samples.     

Modified micro-space using self-organized nanoparticles for reduction of methylene blue

By using silica layers bound to the surface of the inner wall of the microchannel via a self-assembly technique which relies on capillary forces to organize the colloids, TiO2 particles were attached to the inner surface of a microcapillary. The reduction rate of methylene blue increased by more than 150 times in the SiO2/TiO2 modified micro-space compared to that in a batch system.     

In situ preparation of polyaniline coated fumed and precipitated silica fillers and their composites with nitrile rubber (Investigation on structure-property relationship)

In situ synthesis of polyaniline (PAni) coated pyrogenic or fumed silica (PCFS) and precipitated silica (PCPS) were carried out by the oxidative polymerization of aniline in presence of fumed silica (FS) and precipitated silica (PS). Both uncoated and PAni coated silica fillers were characterized through scanning electron microscope (SEM), infrared spectroscopy and thermo-gravimetric analysis (TGA) to evaluate particle morphology and physico-chemical character of coated and uncoated silica particles. Semi-conducting composites made from two different types of PAni coated silica fillers with NBR exhibit different trend in the variation of electrical properties under different temperature and pressure. These differences in electrical properties of two types of composites are mainly due to physico-chemical characteristics of filler particles as well as their distribution in the polymer matrix. This type of composites may be used as semi-conducting and ESD (electrostatic discharge) material.     

Effect of pH on the synthesis and properties of luminescent SiO2/calcium phosphate:Eu3+ core-shell nanoparticles

A novel method for the synthesis of luminescent SiO(2)/calcium phosphate (CaP):Eu(3+) core-shell nanoparticles (NPs) was developed via a sol-gel route followed by annealing at a temperature of 800 °C. The object of this study was the investigation of the effect of pH on the formation of a CaP shell around the silica core. The resulting annealed NPs exhibited an amorphous SiO(2) core and a crystalline luminescent shell. The formation of a CaP layer was possible at pH below 4.5 and above 6.5 during the coating step. The crystal structure of the shell was studied by X-ray diffraction analysis. Hydroxyapatite (HAp) and α-tricalcium phosphate were detected as crystal phases of the surrounding layer. However, NPs produced under basic conditions exhibited a higher crystallinity of the CaP layer than did samples coated at pH below 4.5. In the pH interval between 4.5 and 6.5, no shell growth but the formation of secondary NPs containing CaO and Ca(OH)(2) was observed. Furthermore, SiO(2)/CP:Eu(3+) core-shell NPs were investigated by transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy. The resulting HAp-coated NPs were successfully tested by a cell-culture-based viability assay with respect to a later application as a luminescent marker for biomedical applications.     

Molecular dynamics simulation of amorphous SiO2 nanoparticles

Molecular dynamics simulation of amorphous SiO2 spherical nanoparticles has been carried out in a model with different sizes, 2, 4, and 6 nm, under non-periodic boundary conditions. We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of amorphous nanoparticles obtained at 350 K have been studied via partial radial distribution functions (PRDFs), mean interatomic distances, coordination numbers, and bond-angle distributions, which are compared with those observed in the bulk. Calculations of the radial density profile in nanoparticles show the tendency of oxygen to concentrate at the surface as observed previously in other amorphous clusters or thin films. Size effects on structure of nanosized models are significant. The calculations show that if the size is larger than 4 nm, amorphous SiO2 nanoparticles have a distorted tetrahedral network structure with the mean coordination number ZSi-O approximately 4.0 and ZO-Si approximately 2.0 like those observed in the bulk. Surface structure, surface energy, and glass transition temperature of SiO2 nanoparticles have been obtained and presented.     

Raman Spectra of Molecules Adsorbed on Ag Centers in Sol-Gel Matrices

Silica monoliths and submicron spheres containing silver nanoparticles have been obtained using the sol gel technology. The Ag inclusions were synthesized via the counterdiffusion method. The silver-doped matrices were immersed in solutions of an organic dye (indocyanine green) enabling the solute molecules to interact with surface of the Ag-doped silica matrices. Raman spectra of free solutions of the organic molecules under investigation, the impregnated Ag-doped matrices and the impregnated Ag-free matrices have been measured. The impregnated silica matrices which did not contain silver nanoparticles were used as a reference. These experiments have been performed in order to establish if Raman signal enhancement could be obtained by adsorption of organic molecules on the surface of Ag inclusions in the sol-gel matrices analogously to the standard surface-enhanced Raman spectroscopy (SERS) method.     

LiMn2O4表面包覆Li4Ti5O12的制备及倍率特性

采用固相法合成了尖晶石型LiMn₂O₄，并通过溶胶-凝胶法制备了不同物质的量的百分比含量Li₄Ti₅O₁₂包覆的正极材料。X-射线衍射和扫描电镜结果表明，Li₄Ti₅O₁₂微粒包覆在LiMn₂O₄的表面没有产生晶体结构的变化。实验电池在室温下，以1C，2C和5C倍率作充放电循环测试；结果表明，与未包覆的LiMn₂O₄相比，表面包覆Li₄Ti₅O₁₂微粒的正极材料在高倍率下具有更好的循环稳定性。     

New fluorinated oxazoline block copolymer lowers the adhesion of platelets on polyurethane surfaces

We have prepared an amphiphilic oxazoline block copolymer of hydrophilic poly(2-methyl-2-oxazoline) and hydrophobic poly[2-(2-perfluorooctyl)ethyl-2-oxazoline] chains. By controlling the length and composition of polymer chains, we found that this fluorinated block copolymer can be readily dissolved in water. Furthermore, we can achieve a stable surface coating of the fluorinated block copolymer by dissolving the copolymer in water, then coating the aqueous copolymer solution onto surfaces of nonwater-soluble polymers. This is a simple and useful method of modifying the surface character of polymer substrates. We have found that the polyether urethane (PEU) coated by block copolymer has a different surface chemistry and biological reactivity than the uncoated PEU. From XPS analysis, we found the fluorinated copolymer was coated on PEU (atomic % of F: 31.3 on coated PEU, 0.3 on uncoated). The two surfaces have different affinities for biological molecules. Specifically, the fibrinogen adsorption on the fluorinated copolymer-coated PEU was 62 ± 39 ng/cm², compared to a value of 156 ± 99 ng/cm² for uncoated PEU. In an ex vivo evaluation of platelet adhesion, the surface of coated PEU attached a few white cells while uncoated PEU was covered with activated platelets. © 1994 John Wiley & Sons, Inc.