Silica-based sol-gel films

Ellipsometric study of porosity distribution in hybrid silica-based sol-gel films... 

Almeida R.M. Sol-gel silica films on silicon substrates. Int. J. Optoelectron. 1994 9 135-142 Almeida R.M., Vasconcelos H.C., Ilharco L.M. Relationship between infrared absorption and porosity in silica-based sol-gel films. SPIE Sol-Gel Opt. HI 1994 2288 678-687 Almeida R.M. Spectroscopy and structure of sol-gel systems. J. Sol-Gel Sci. Technol. 1998 13 51-59... 

Marques, A.C., Almeida, R.M., Ramos, A.R., and Alves, E. (2004) Compositional profiles in silica-based sol-gel films doped with erbiiun and silver, by RBS and ERDA. J. Sol-Gel Set TechnoL, 31, 287-291. 

Also, third-generation biosensors for superoxide anion (O ) have been developed based on superoxide dismutase (SOD) immobilised by thin silica-PVA sol-gel film on a gold electrode surface [633]. The preparation of SOD electrode is easy and simple. The uniform porous structure of the silica-PVA sol-gel matrix results in a fast response rate of immobilised SOD and is very efficient for stabilising the enzyme activity. 

However, interest in this approach to enzyme immobilization has recently been renewed by the application of silica-based sol-gel entrapment matrices. These provide mild hydrophilic environments with controlled pore sizes. Moreover sol-gels can be formed into optically clear monoliths of varying dimensions, thin films, and fibers. Several applications including the determination of metal ions and of peroxidase have already been described. 

Sol-gel-derived silane-based materials have been proven as a suitable matrix for entrapment of bioactive species, due to biocompatibility of silica and the mild operating conditions. We recall that the solutions used for cathodic electrochemical deposition of silane-based sol-gel films are usually mild acidic (pH 3-6), and the deposition is achieved by electrochemically driving the inter- cial pH near the cathode to mild basic, about pH 8. This environment is favorable for maintaining the activity of biological species such as proteins, enzymes, and bacteria. Many researchers have reported the fabrication of biosensing films by co-electrodeposition of silane with different bioactive substances. The essence of the concept is to entrap bioactive substances within the sol-gel matrix during... 

Over the last several years, the number of studies on application of artificial neural network for solving modeling problems in analytical chemistry and especially in optical fibre chemical sensor technology, has increase substantially69. The constructed sensors (e.g. the optical fibre pH sensor based on bromophenol blue immobilized in silica sol-gel film) are evaluated with respect to prediction of error of the artificial neural network, reproducibility, repeatability, photostability, response time and effect of ionic strength of the buffer solution on the sensor response. 

Q.L. Wang, G.X. Lu, and B.J. Yang, Hydrogen peroxide biosensor based on direct electrochemistry of haemoglobin immobilized on carbon paste electrode by a silica sol-gel film. Sens. Actuators, B Chem. 99, 50-57 (2004). 

The incorporation of Ru(II) chelates in various types of silica sol-gel-based composite films is another mode of immobilization.262,280-284 Silica sol-gel materials provide some advantages over organic polymers such as the ease with which they can be prepared, modified, and doped with various reagents. Particularly, silica sol-gel films are stable upon continuous electrochemical oxidation or upon drying the gels in a high humidity environment. 

Similarly, CdS NCs capped with mercaptopro-pyltrimethoxysilane (MPTMS) were added to alcohohc solutions of TEOS or TMOS and subsequently incorporated into sihca matrices. Pb and Hg-based NCs have also been synthesized with MPTMS as the capping agent, and the role of the pendant siloxy groups is again to anchor the NCs to the sihca, silica-titania, or zirconia networks. Zirconia films doped with PbS NCs were prepared with refractive indices up to 1.53 and a third-order susceptibility value of 1.3 X 10 esu. Higher refractive index sihca-titania sol gel films doped with PbS (n = 1.63) were also fabricated. ... 

Fabry-Perot etalon devices based on materials sensitive to electric fields have been studied as tuneable optical filters. Gan et al. [165] presented in their work a hybrid organic/inorganic sol-gel material based on 3-methacryloxypropyl trimethoxysilane as precursor and TCBD (15% mol) as NLO chromophore that was covalently incorporated into the silica network. They demonstrated an optical filter having large tunability and high finesse. The EO sol-gel film was corona poled with 5 kV/cm at 170°C for 30 min. 

Wei, W., Zong, X., Wang, X. et al. (2012) A disposable amperometric immunosensor for chlorpyrifos-methyl based on immunogen/platinum doped silica sol-gel film modified screen-prinfed carbon elecfrode. Food Chem., 135, 888-892. 

Figure 26-7. Representative AFM (height) images and selected cross-sectional profiles for (a) acid-catalyzed, and (b) base-catalyzed silica sol/gel films coated with aminopropyl-triethoxysilane (APS). Iheheightimagesare 1 fim x 1 fimbig with a z-range of 5 and 20 nm for (a) and (b), respectively with the RMS surface roughness values of 6 and 25 A.

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