Ormosil Encapsulated Pyrroloquinoline Quinone‐Modified Electrochemical Sensor for Thiols

An organically modified sol‐gel glass (ORMOSIL) encapsulating pyrroloquinoline quinone (PQQ)‐modified electrode for the rapid, sensitive and simple determination of thiol‐containing compounds such as cysteine and glutathione is reported. The effect of applied potential, nature of thiol compound and pH on the response of the sensor was examined and optimum conditions were determined. The electrochemical responses and detection limits were found to be sensitive to the nature of thiols and pH. The electrochemical responses for cysteine and glutathione at an applied potential of ?0.2 V (vs. Ag/AgCl) were found to be linear with detection limits of 18 nM for cysteine and 36 nM for glutathione at pH 3.5, whereas the detection limits at pH 8.5 were 0.5 μM for cysteine and 1 μM for glutathione. The electrode retained 95% of the original response for 7 days when stored at 4 °C. The ORMOSIL‐encapsulated PQQ was also characterized by spectrophotometry. The absorbance measurement using 5,5′‐dithiobis(2‐nitrobenzoic acid) at 412 nm justify the PQQ‐mediated oxidation of glutathione whereas fluorescence measurements (excitation wavelength=380 nm; emission wavelength=480 nm) justify the successful encapsulation of PQQ in ORMOSIL matrix.     

Stabilization of catalytic sol-gel entrapped perruthenate

A combination of more stable counter-cation (tetraphenylphosphonium in place of tetrapropylammonium), of local basic microenvironment, and of a non-solubilizing reaction medium (supercritical CO₂) improves the life-cycle and reusability of catalytic ORMOSILs doped with perruthenate in the oxidation of alcohols with O₂. A number of different bases were co-entrapped and their effect on catalysis assessed in the oxidative dehydrogenation of benzyl alcohol in dense phase carbon dioxide at 22 MPa and 75 °C. The optimized catalyst retains most of its activity after five consecutive runs when a normal ORMOSIL-entrapped TPAP has become inactive. Deactivation of TPAP could be ascribed by EPR analysis to the formation of catalytically inactive RuO₂.     

The use of LCMS as an analytical tool for hydrolysis/polycondensation monitoring of a chiral ORMOSIL precursor

The kinetic of the sol–gel hydrolysis and polycondensation reactions of a chiral ORMOSIL precursor was investigated by LCMS technique as a function of water excess and pH. While the amount of water does not significantly change the kinetics, the reactions strongly depend on the [H]⁺ concentration. At pH ≤ 3, the hydrolysis is very fast and the conversion of the precursor is completed within less than 1 h whereas at 80% of the precursor is still present after 50 h at pH = 3.5. This kinetic study allows to define a set of initial conditions and time ranges required to provide good optical quality dip coated films .

Novel Nafion®/ORMOSIL hybrids via in situ sol-gel reactions: 2. Probe of ORMOSIL phase nanostructure by 29Si solid state NMR spectroscopy

Perfluorosulfonic Acid (PFSA)]/[Organically-Modified Silicon Oxide (ORMOSIL)] hybrids were formulated via sol-gel reactions of mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) in the nanophase-separated morphology of a PFSA membrane (Nafion^®). The molecular structures of the ORMOSIL phases were investigated by ²⁹Si solid state NMR spectroscopy and the spectra compared with those of corresponding bulk ORMOSILs. PFSA-in situ ORMOSIL composition can be tailored by manipulating TEOS/DEDMS source solution composition and quantified by ²⁹Si solid state NMR spectroscopy. Copolymerization of TEOS and DEDMS monomers, rather than block formation, occurs within the PFSA as well as in the bulk. As DEDMS feed concentration increases, ORMOSIL nanostructures are more hydrophobic and more flexible. Dimethylsiloxane rings are dominant in PFSAs in which hydrolysis + condensation of pure DEDMS occurs.     

Preparation of Microporous ORMOSILs by Thermal Degradation of Organically Modified Siloxane Resin

Silicon containing materials have traditionally been used in microelectronic fabrication. Semi-conductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements forming an integrated circuit. These interconnect levels are typically separated by an insulating or dielectric film. Previously, a silicon oxide film was the most commonly used material for such dielectric films having dielectric constants (k) near 4.0. However, as the feature size is continuously scaling down, the relatively high k of such silicon oxide films became inadequate to provide efficient electrical insulation. As such, there has been an increasing market demand for materials with even lower dielectric constant for Interlayer Dielectric (ILD) applications, yet retaining thermal and mechanical integrity. We wish to report here our investigations on the preparation of ultra-low k ILD materials using a sacrificial approach whereby organic groups are burnt out to generate low k porous ORMOSIL films. We have been able to prepare a variety of organically modified silicone resins leading to highly microporous thin films, exhibiting ultra-low k from 1.80 to 2.87, and good to high modulus, 1.5 to 5.5 GPa. Structure property influences on porosity, dielectric constant and modulus will be discussed.     

A Spectroscopic Study of the Effects of Various Solvents and Sol-Gel Hosts on the Chemical and Photochemical Properties of Thionin and Nile Blue A

Tetraethyl orthosilicate (TEOS)-based gels were doped with two optically active organic indicators, thionin and nile blue A. Before trapping in a sol-gel host, thionin and nile blue A were both evaluated for solvent and protonation effects on their spectral properties. Only extreme pH values provided by HCl, NaOH, and NH₄OH produced new absorption and/or fluorescence bands. Introduction of nile blue A into alkaline environments (0.1N NaOH, NH₄OH) results in the appearance of a broad absorption band centered near 520 nm whereas highly acidic environments (1N HCl) show a reduction of the 635 nm absorption peak accompanied by an absorption band located near 460 nm. A marked decrease is observed in the optical density of thionin in 1N HCl solution which results in a reduction in the fluorescence intensity. The absorption and fluorescence spectra also reveal a decrease in a pH 11 solution of NH₄OH as compared to neutral conditions. Both dyes formed dimers when the sol-gel host, initially synthesized with TEOS, was organically modified with methyltrimethoxysilane (MTMS). However, thionin dimers were present in all silica-based sol-gel compositions, as evidenced by the absorption and fluorescence spectra. Substitution of MTMS for some of the TEOS in the gel matrix resulted in blue shifts in the absorption and fluorescence spectra of nile blue A. The absorption peak shifted 50 nm to 596 nm whereas the fluorescence shifted around 40 nm to 635 nm. These blue shifts resulted from the reduced polarity of the silica-based xerogel. Thionin also exhibited shifts in its absorption and fluorescence spectra with organic modification by MTMS. The absorption shifted approximately 3 nm to 595 nm while the fluorescence maximum decreased 7 nm to 630 nm. The blue shifts in the spectra of thionin with additions of MTMS were attributed to surface sites that altered the molecular structure of the adsorbed thionin molecules.     

Effects of pH During the Base Catalyzed Reaction of Two-Step Acid/Base Catalyzed Process on the Microstructures and Physical Properties of Poly(dimethylsiloxane) Modified Silica Xerogels

Poly(dimethylsiloxane) (PDMS) modified silica xerogels were prepared by two-step acid/base catalyzed sol-gel process. By keeping the acid amount and hydrolysis period in acidic environment fixed, and adding different amounts of base to the sol afterwards, attempts had been made to study the effect of the different amounts of base catalyst on the micro-structure and physical properties of the prepared ORMOSILs. DTA, SEM, BET, FTIR were performed to characterize the derived specimens. The microstructure and physical properties are greatly influenced by the amount of base added to the sol. With increasing base content the crystallite size and porosity increase and the pore size distribution takes a broad spectrum. Whereas, the glass transition temperature seems to decrease with increasing of base catalyst amount. This is explained in terms of the change in the relative amounts of hydrolysis and condensation reactions due to the addition of different amount of base catalyst, which predominantly influences the condensation reactions. The results are reported in this communication along with possible explanations behind the observations.     

Design of an end station for a high current ion implantation system

Single crystal silicon has been implanted with nitrogen and phosphorus ions at MeV energies to fluences between 10¹⁶ and 1.6 × 10¹⁸ ions/cm₂. Infrared transmission and reflection spectra in the range of 1.25 to 40 μm were measured for as-implanted samples and after various annealing treatments. Interference fringes were observed in the IR spectra which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringe structure, we obtained refractive index profiles, which, under suitable interpretation, provide accurate measurements and several quantities of interest. These quantities are the range and straggling of the implanted ions, the depth of disordered layers, and the width of the order-disorder transition. Mechanisms for the refractive index changes which have been identified include amorphization of the implanted silicon, bulk compositional change in the buried layer, localized vibrational mode dispersion, and free electron dispersion. Experimental results and theoretical predictions are presented, demonstrating each of these mechanisms.     

Spontaneous formation of silver nanoparticles in aminosilica

We report a rapid and spontaneous metallization process associated with sol–gel reaction of aminosilane that can be utilized to synthesise silver embedded silica nanocomposite without involving additional reducing agents. The reduction reaction induced by bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS) involves amine functional moieties, which drive the reduction reaction with presence of water. Cyclic voltammetry was used to investigate the redox potential of enTMOS and its relation to chemical environment. It was found that the oxidation potential of enTMOS depending on the amount of water (water:enTMOS (v/v) = 8:1–0:1) ranges from 0.48 to 0.68 V versus Ag/AgCl electrode in methanol. The oxidation potential of aminosilane decreases with water content and becomes more negative than that of Ag, suggesting the aminosilane acts as a silver reducing agent while serving as a matrix to encapsulate silver nanoparticles after reacting with water. This process has been utilized to produce evenly dispersed silver nanoparticles with sizes ranging from 5 to 20 nm in both liquid and solid forms of aminosilane, allowing us to prepare silver nanoparticles doped silica nanocomposite that exhibits enhanced electrochemical properties.     

Electrical Properties of Sol-Gel Processed Hybrid Films

We report on the electrical properties of a hybrid organic/inorganic material synthesized by a sol-gel technique. Spin-coated films with sputtered Nb electrodes in a sandwich-type geometry were studied by a.c. measurements. The aging of the films affected the resistance of the samples. Electrochemical impedance spectroscopy (EIS) measurements were performed in a test chamber at different relative humidity (RH) values to evaluate the aging mechanism.