Sol-gel Technology for Sensor Applications

Abstract

Sol-gel processes refer to the transition of predefined compositions of inorganic alkoxides precursors from liquid sol phase to solid gel phase. The phenomenon of sol-gel was known to mankind for more than 150 years. It is because of concerted efforts of researchers from multidisciplinary fields, sol-gel science transformed to technology. Several products are already commercially available for applications in optical coatings, nanocomposites, and public healthcare. Potential applications in the areas of biosensors and environmental monitoring are expected. Newer applications with nanotechnology appear too exciting. An attempt has been made to address important applications of sol-gel technology, particularly in sensing techniques from the defence perspective.Keywords: Sol-gel technology, nanomaterials, healthcare, sensors, defence applications Revised 19 November 2006 . INTRODUCTIONThe term sol-gel was first coined in the late 1800s. It generally refers to a low-temperature method using inorganic precursors that can produce ceramics and glasses with better purity and homogeneity than through high temperature conventional processes 1 . Two most attractive features of the sol-gel process are that it can produce compositions that cannot be created with conventional methods, and that the mixing level of the solution is retained in the final product, often up to the molecular scale.Sol-gel method has been successfully used to manufacture a variety of products, viz., bulk glasses 2 , optical fibers 3 , special coatings, ultra-pure powders, and multifunctional materials. Figure 1 shows different types of materials made from sol-gels. Sol-gelprocessed transparent porous matrix offers the possibility of doping various organic and inorganic molecules [5][6][7][8] . Sol-gel process has been used to Defence Science Journal, Vol. 57, No. 3, May 2007, pp. 241-253 © 2007 241 REVIEW PAPERfabricate materials which can be used as new laser materials, nanocomposites, biomimetic systems, and so on. Because of potential in fabrication of a wide variety of new materials, understanding of sol-gel processes has become the centre of interdisciplinery research, viz., physics, chemistry, biology, biotechnology, biochemistry, electronics, and related engineering branches. Sol-gel materials have a wide range of applications, from environmental monitoring, biosensors for healthcare, to nanotechnology for sensing clinically-important analytes. . BASICS OF SOL-GEL PROCESSThe sol-gel process is a versatile technique which involves the transition of a predefined composition from liquid sol (mostly colloidal) phase into a solid gel phase 9 . Sol-gel processing involves the hydrolysis of a metal alkoxide followed by condensation and polymerisation reactions, leading to the sol-gel state.242 DEF SCI J, VOL. 57, NO. 3, MAY 2007 These general reactions are shown below:Metal alkoxides are most popular because these react readily with water. The most widely used metal alkoxides are the alkoxysilanes, such as tetramethoxysilane (TMOS) a...

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Nanostructured thin films for icephobic applications =

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