Organically Modified Silicate Research Articles

Optical biosensor for the determination of BOD in seawater

An automatic sensing system was developed using an optical BOD sensing film. The sensing film consists of an organically modified silicate (ORMOSIL) film embedded with an oxygen-sensitive Ru complex. A multi-microorganisms immobilization method was developed for the BOD sensing film preparation. Three different kinds of microorganisms, Bacillus licheniformis, Dietzia maris and Marinobacter marinus from seawater, were immobilized on a polyvinyl alcohol ORMOSILs. After preconditioning, the BOD biosensor could steadily perform well up to 10 months. The linear fluctuant coefficients ( R 2) in the range of 0.3–40 mg L −1 was 0.985 when a glucose/glutamate BOD standard was applied. The reproducible response for the BOD sensing film could be obtained within ±2.3% of the mean value in a series of 10 samples in 5.0 mg L −1 BOD standard GGA solution. The effects of temperature, pH and sodium chloride concentration on the two microbial films were studied as well. The BOD sensing system was tested and applied for the BOD determination of seawater.

Domieszkowane uklady polimerowe wytwarzane metoda zol-zel: wlasciwosci optyczne i potencjalne zastosowanie przemyslowe

A review of the studies on sol-gel technology application to the production of doped polymeric systems, which can be applied as new optical materials: tunable lasers, sensors, waveguides, photochromic or electrochromic materials and semiconductors. Sol-gel method based on hydrolysis and subsequent polycondensation of precursors, such as organo-silicon alkoxides (Scheme A), leading to formation of porous glass was described. The matrices for incorporation of organically active dopants in are produced from this glass. The matrices can be the glass/polymer composites, organically modified silicates (ORMOSIL) or hybrid materials zirconia - silica - polyurethane (ZSUR) (Schemes B-E). The characteristics of examples of laser dyes forming the solid tunable lasers are given. Finally, the description of semiconductors produced by incorporation of nanoparticles into the matrices discussed has been presented.

Better Chemistry through Ceramics: The Physical Bases of the Outstanding Chemistry of ORMOSIL

Twenty years after their invention, sol-gel organically modified silicates (ORMOSIL) are finding a number of impressive applications that range from efficient deliver of genes into mouse brains to self-ordered helices of interest to fields as diverse as optics, catalysis, molecular recognition, and chromatography. The physical bases of this mulifaceted chemistry, therefore, are of immense importance to scientists working toward new applications such as photovoltaics and catalysis that are crucially important in making sustainable global development. The purpose of this article is to provide a general picture of ORMOSIL's physical chemistry that will be useful in the creative development of new materials capable to solve a number of relevant open problems.

Electrochemiluminescent behaviors of alkaloids and tris(2,2′-bipyridine) ruthenium in organically modified silicate film

Electrogenerated chemiluminescences (ECLs) of alkaloids, such as berberine, trigonelline, allantoin and betaine, were studied in an aqueous alkaline buffer solution (pH 9.5), based on tris(2,2′-bipyridine)ruthenium(II) [Ru(bpy) 3 2+] immobilized in organically modified silicates (ORMOSILs) film on a glassy carbon electrode (GCE). The immobilized Ru(bpy) 3 2+ showed good electrochemical and photochemical activities. In a flow system, the eluted alkaloids were oxidized on the modified GCE, and reacted with immobilized Ru(bpy) 3 2+ at the potential of +1.50 V (versus Ag/AgCl). The luminescence with λ max 610 nm was caused by a reaction of electrolytically formed Ru(bpy) 3 3+ with an oxidized amine group to generate Ru(bpy) 3 2+*. The determination limit was 5 × 10 −6 mol L −1, 8 × 10 −6 mol L −1, 2.0 × 10 −5 mol L −1 and 5.0 × 10 −5 mol L −1 for berberine, trigonelline, allantoin and betaine at S/N 3, respectively. In addition, the factors affecting the determination of the four alkaloids were also studied.

Role of the Alkyl−Alkoxide Precursor on the Structure and Catalytic Properties of Hybrid Sol−Gel Catalysts

Detailed diffuse-reflectance infrared Fourier transform structural analysis of a series of organically modified silicates (ORMOSIL)-entrapped catalysts, varying the molar percentage and the alkyl chain length of the organic group, shows that the important factors affording optimal catalytic performance are two: predominance of six-member siloxane rings (above 80% alkylation) and a low hydrophilicity−lipophilicity balance (HLB). These results provide investigators engaged in developing novel catalysts based on the sol−gel routean advanced chemical technology for synthetic organic/inorganic chemistrywith general guidelines to prepare optimal catalytic materials for a number of relevant applications.

Ratiometric Singlet Oxygen Nano‐optodes and Their Use for Monitoring Photodynamic Therapy Nanoplatforms

Ratiometric photonic explorers for bioanalysis with biologically localized embedding (PEBBLE) nanoprobes have been developed for singlet oxygen, using organically modified silicate (ORMOSIL) nanoparticles as the matrix. A crucial aspect of these ratiometric singlet-oxygen fluorescent probes is their minute size. The ORMOSIL nanoparticles are prepared via a sol-gel-based process and the average diameter of the resultant particles is about 160 nm. These sensors incorporate the singlet-oxygen-sensitive 9,10-dimethyl anthracene as an indicator dye and a singlet-oxygen-insensitive dye, octaethylporphine, as a reference dye for ratiometric fluorescence-based analysis. We have found experimentally that these nanoprobes have much better sensitivity than does the conventional singlet-oxygen-free dye probe, anthracene-9,10-dipropionic acid disodium salt. The much longer lifetime of singlet oxygen in the ORMOSIL matrix, compared to aqueous solutions, in addition to the relatively high singlet oxygen solubility because of the highly permeable structure and the hydrophobic nature of the outer shell of the ORMOSIL nanoparticles, results in an excellent overall response to singlet oxygen. These nanoprobes have been used to monitor the singlet oxygen produced by "dynamic nanoplatforms" that were developed for photodynamic therapy. The singlet oxygen nanoprobes could potentially be used to quantify the singlet oxygen produced by macrophages.

Novel BOD optical fiber biosensor based on co-immobilized microorganisms in ormosils matrix

A biochemical oxygen demand (BOD) sensor has been developed, which is based on an immobilized mixed culture of microorganisms combined with a dissolved oxygen (DO) optical fiber. The sensing film for BOD measurement consists of an organically-modified silicate (ORMOSIL) film embedded with tri(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) perchlorate and three kinds of seawater microorganisms immobilized on a polyvinyl alcohol sol-gel matrix. The BOD measurements were carried out in the kinetic mode inside a light-proof cell and with constant temperature. Measurements were taken for 3 min followed by 10 min recovery time in 10 mg/L glucose/glutamate (GGA) BOD standard solution, and the range of determination was from 0.2 to 40 mg/L GGA. The effects of temperature, pH and sodium chloride concentration on the BOD sensing films were studied. BOD values estimated by this optical BOD sensing film correlate well with those determined by the conventional BOD5 method for seawater samples.

Photostability of laser dyes incorporated in formamide SiO2 ORMOSILs

The sol–gel process provides a low temperature chemical route for the preparation of rigid transparent matrix materials. Under this process, luminescent organic dye molecules were incorporated into organically modified silicate (ORMOSIL) host matrices. The photostability of these laser dyes encapsulated in a solid matrix was studied using optical absorption and luminescence. The photochemical mechanisms of the dye response under N2 laser irradiation were studied using UV and fluorescence spectra measurement. The evolution of the maximum of the emission and excitation curves as function of accumulated irradiated energy was fitted by exponential equations. The matrix protects the dye from the oxidation and dimerization reactions. The dye molecules exhibited photobleaching due to their photodegradation. The ORMOSIL doped with Nile blue exhibits good photostability after 6 h of irradiation.

Gaining Insight into the Nanoscale Properties of Sol−Gel-Derived Silicate Thin Films by Single-Molecule Spectroscopy

The application of single-molecule spectroscopic methods in studies of individual nanoscale environments within sol-gel-derived silicate thin films is reviewed. Representative examples of the experiments performed and results obtained in several studies from the authors' laboratories are given. Included are investigations of the static and dynamic polarity properties of organically modified silicate (ORMOSIL) films. The results of these studies point to nonrandom variations in the film properties, providing strong evidence for the formation of phase-separated organic- and inorganic-rich domains. Studies of single-molecule diffusion through the same films yield important evidence for the formation of liquidlike silicate oligomers that facilitate probe molecule diffusion. Finally, single-molecule studies of the local pH within individual film environments are discussed. Valuable information on the contributions of local materials' acidity variations to overall sample heterogeneity is obtained. The results of immersion studies indicate that certain molecular environments are inaccessible to external solutions over periods as long as a few hours. The article concludes with a discussion of possible future challenges in this research that may be addressed by new and existing single-molecule methods.

Poly[styrene-b-maleated (ethylene/butylene)-b-styrene] (mSEBS) block copolymers and mSEBS/inorganic nanocomposites: I. Morphology and FTIR characterization

Self-assembled, [block copolymer]/[pure silicate and ORMOSIL] nanocomposites were created via sol–gel processes for silicate and organically-modified silicate (ORMOSIL) monomers in the presence of sulfonated maleated poly(styrene-b-ethylene/butylene-b-styrene) (mSEBS). Microscopic and small angle X-ray scattering (SAXS) studies showed that unmodified mSEBS has hexagonal packed PS cylinder morphology, but sulfonation causes the morphologies to be frustrated. The morphology of pure silicate nanoparticle-containing nanocomposites is phase separated, although further frustrated. The morphologies of the ORMOSIL-modified materials were different, less-ordered and show the influence of the nature of the organic group on self-assembly. Despite differences in morphology, degree of order, and different inter-domain spacings, all but the pure silicate-containing hybrid have the same PS domain width (25–30nm). The dispersed nanoparticles are roughly spherical and some can grow to exceed the block copolymer domain sizes. All filled samples have inter-domain spacings, derived by SAXS analysis, that are larger than that of the corresponding unfilled sulfonated mSEBS, which reflects insertion of silicate or ORMOSIL structures. FTIR spectroscopy indicated successful Si–O–Si bond formation, which shows that the inserted particles are indeed crosslinked.

Luminescence and laser performances of coumarin dyes doped in ORMOSILs

Laser dyes such as coumarin 440 (C440) and coumarin 500 (C500) were doped into vinyltriethoxysilane (VTES)-derived organically modified silicates (ORMOSILs) by sol–gel process. The fluorescence properties of these two dyes doped in VTES-derived ORMOSILs with various initial dye concentrations were studied. A longitudinal pumped solid-state dye laser was established with a Q-switched Nd:YAG laser source. The laser performances of C440 and C500 dyes doped in VTES-derived ORMOSILs were also measured.

Methods for modifying proton exchange membranes using the sol–gel process

Over the past 20 years, sol–gel processing has expanded into organic–inorganic hybrid materials. This expansion has benefited from the collaborations between the polymers community and the ceramics community, and the discovery that in many instances sol–gel processing and polymer processing are compatible. An active participant in this field has been Dr James E. Mark [Mark JE. Heterog Chem Rev 1996;3:307–320], and his accomplishments deserve this tribute. One example, which derives from his work in organically-modified silicates (ORMOSILS), is hybrid membranes for fuel cells. We present some recent progress in synthesis of hybrid membranes involving Nafion. These membranes have been prepared by infiltration and recasting, and contain silicates, phosphosilicates, zirconium phosphosilicates and titanosilicates.

Photodynamic Characterization and In Vitro Application of Methylene Blue‐containing Nanoparticle Platforms¶

ABSTRACTThis article presents the development and characterization of nanoparticles loaded with methylene blue (MB), which are designed to be administered to tumor cells externally and deliver singlet oxygen (1O2) for photodynamic therapy (PDT), i.e. cell kill via oxidative stress to the membrane. We demonstrated the encapsulation of MB, a photosensitizer (PS), in three types of sub‐200 nm nanoparticles, composed of polyacrylamide, sol‐gel silica and organically modified silicate (ORMOSIL), respectively. Induced by light irradiation, the entrapped MB generated 1O2), and the produced 1O2 was measured quantitatively with anthracene‐9, 10‐dipropionic acid, disodium salt, to compare the effects of different matrices on 1O2 delivery. Among these three different kinds of nanoparticles, the polyacrylamide nanoparticles showed the most efficient delivery of 1O2 but its loading of MB was low. In contrast, the sol‐gel nanoparticles had the best MB loading but the least efficient 1O2 delivery. In addition to investigating the matrix effects, a preliminary in vitro PDT study using the MB‐loaded polyacrylamide nanoparticles was conducted on rat C6 glioma tumor cells with positive photodynamic results. The encapsulation of MB in nanoparticles should diminish the interaction of this PS with the biological milieu, thus facilitating its systemic administration. Furthermore, the concept of the drug‐delivering nanoparticles has been extended to a new type of dynamic nanoplatform (DNP) that only delivers 1O2. This DNP could also be used as a targeted multifunctional platform for combined diagnostics and therapy of cancer.

High-Performance Quenchometric Oxygen Sensors Based on Fluorinated Xerogels Doped with [Ru(dpp)3]2+

By using hybrid xerogels that are composed of alkyl and perfluoroalkyl ORMOSILs (organically modified silicates) doped with the luminophore tris(4,7'-diphenyl-1,10'-phenanthroline) ruthenium(II), we have produced highly sensitive O2 sensors (i.e., I(N2)/I(O2) = 35 +/- 4) with linear calibration curves that exhibit less than 2% drift over 6 months.

Vibrational spectroscopic studies of sol–gel derived physical and chemical bonded ORMOSILs

Fourier transform infrared (FT-IR) and FT-Raman Spectroscopy have been utilized to characterize the structure of physical and chemical bonded ORMOSILs (organically modified silicates) and to compare with the physical properties, reported earlier. The classic and sono ORMOSILs were synthesized by sol–gel method via traditional- and sono-catalysis routes, respectively. The physical and chemical bonding is established by Poly(ethylene glycol) (PEG) and Poly(dimethoxysilane) (PDMS), respectively. Existence of band at ∼560 cm −1 (FT-IR) and ∼490 cm −1 (FT-Raman) for the sono and classic gels with 5–10 wt% of PEG indicates the presence of structural defect due to the four-membered siloxane rings. Application of long molecular PEG chain and PDMS increases this defect. Modification in the intensity and peak position of siloxane (Si–O–Si) bands is found correlative with the physical properties. The xerogels with 5–10 wt% of PEG possess a large number of residual surface silanol groups than the xerogels with long molecular PEG chains and PDMS and is found related with the ν(OH) band at ∼3470 cm −1. These results are attributed to the way of hydrolysis–condensation reactions and discussed with the help of Percolation and DLVO models.

Energy transfer mechanism between laser dyes doped in ORMOSILs

Laser dyes perylene orange (p-orange) or perylene red (p-red) or pyrromethene 567 (p567) were co-doped with coumarin 440 (C440) or coumarin 500 (C500) into MTES- and VTES-derived organically modified silicates (ORMOSILs) by sol–gel process. Energy transfer from both C440 and C500, energy donors, to p-red, p-orange and p567, acceptor, respectively, has been observed and studied by steady-state emission measurement. The effect of donor concentration on energy transfer and its mechanism were studied. The potential application as an energy transfer dye laser (ETDL) was also discussed. At least 1-fold increase in the slope efficiency of p-red and 3-fold increase in the photostability of p567 was observed in such ETDLs.

Photodynamic Characterization and In Vitro Application of Methylene Blue-containing Nanoparticle Platforms¶

This article presents the development and characterization of nanoparticles loaded with methylene blue (MB), which are designed to be administered to tumor cells externally and deliver singlet oxygen (1O2) for photodynamic therapy (PDT), i.e. cell kill via oxidative stress to the membrane. We demonstrated the encapsulation of MB, a photosensitizer (PS), in three types of sub-200 nm nanoparticles, composed of polyacrylamide, sol-gel silica and organically modified silicate (ORMOSIL), respectively. Induced by light irradiation, the entrapped MB generated 1O2, and the produced 1O2 was measured quantitatively with anthracene-9,10-dipropionic acid, disodium salt, to compare the effects of different matrices on 1O2 delivery. Among these three different kinds of nanoparticles, the polyacrylamide nanoparticles showed the most efficient delivery of 1O2, but its loading of MB was low. In contrast, the sol-gel nanoparticles had the best MB loading but the least efficient 1O2 delivery. In addition to investigating the matrix effects, a preliminary in vitro PDT study using the MB-loaded polyacrylamide nanoparticles was conducted on rat C6 glioma tumor cells with positive photodynamic results. The encapsulation of MB in nanoparticles should diminish the interaction of this PS with the biological milieu, thus facilitating its systemic administration. Furthermore, the concept of the drug-delivering nanoparticles has been extended to a new type of dynamic nanoplatform (DNP) that only delivers 1O2. This DNP could also be used as a targeted multifunctional platform for combined diagnostics and therapy of cancer.

Use of water to evaluate hydrophobicity of organically-modified xerogel enzyme supports

Silica xerogels are a new class of materials suitable for the immobilization of enzymes for various applications including biotransformations and biosensors. The physicochemical properties of xerogels, such as hydrophobicity, can be manipulated by the introduction of organically-modified silicates. This allows the immobilization matrix to be engineered to suit the enzyme and its application. Interfacial activation of lipase is a phenomenon in which the enzyme displays increased activity when it is bound to a hydrophobic interface. Lipase was entrapped in organically-modified xerogels in which the hydrophobicity of the enzyme support was modulated by the selection of different alkyltrimethoxysilane co-precursors and the ratio in which they were combined with tetramethyl orthosilicate. Interaction between the enzyme support and water was investigated with two methods to quantitatively assess the hydrophobicity of the entrapment matrix. The contact angle formed between the xerogel and water was used to determine hydrophobicity on a macroscopic level. Temperature-controlled water desorption was used to determine hydrophobicity on a microscopic level. Both methods were suitable for quantitatively discriminating between hydrophobic and hydrophilic materials. Further, the hydrophobicity of the enzyme support influenced the hydrolytic activity of the entrapped lipase under non-aqueous conditions. The specific activity of lipase increased only when entrapped in xerogels which could be classified as hydrophobic materials, that is with contact angles greater than 90 degrees or hydrophobicity values as determined by water desorption greater than 0.65.

Synthesis In Situ, Characterization, and Photostability of Europium β-Diketone Chelates in Organically Modified Silicates (ORMOSILs)

Europium β-diketonates have desirable optical properties, and transparent inorganic materials that have been doped with these chelates seem to be promising for potential applications in luminescence-display devices, integrated optical device sources, and new visible lasers. However, these chelates may be decomposed or not dissolved in sol—gel precursor solutions and, thus, cannot be doped in gel glasses that have been prepared via traditional sol—gel processing. An in situ synthesis technique has been used for the first time to synthesize five binary and ternary coordination compounds of europium β-diketonates in transparent organically modified silicates (ORMOSILs) during heat treatment or during the process of sol-to-monolithic ORMOSIL conversion. ORMOSILs that have been doped with in situ europium β-diketonates exhibit rather-high fluorescence intensity and good monochromati-city. These materials result in enhanced red-light emission under ultraviolet excitation. The chelates that have been synthesized in situ in the ORMOSILs reveal better photostability, in comparison to that of the pure chelates that have been dissolved in ethanol solutions.

Luminescent properties of neodymium organic complexes and as-doped organically modified silicate films

Near-infrared (NIR) luminescent ternary and hydrated binary neodymium β-diketonates emitting at ca. 1330 nm are presented. The effects of ligand moieties on the photoluminescence properties of Nd 3+ ions are discussed. Moreover, the neodymium organic complex neodymium tris(2-theonyltrifluoroacetonate)bis(triphenylphosphine oxide), Nd(TTA) 3(TPPO) 2, which has the best photoluminescence properties among all investigated neodymium complexes, is incorporated into vinyltriethoxysilane-derived ORMOSIL (organically modified silicate) film by a multistep sol–gel process. The Nd doping concentration was up to 5 mol% related to Si. The spectroscopic results about as-doped ORMOSIL films indicate that the ligands around Nd 3+ ions indeed shield effectively Nd 3+ ions from luminescence-quenching impurities in the host matrix, such as OH groups.