An entirely novel materials technology has been developed at The Hebrew University of Jerusalem. It allows for the first time, to incorporate within ceramic materials organic and bioorganic molecules. Traditionally, this has been impossible, because of the very high temperatures employed in glasses and ceramic technology. Now, the properties of ceramic materials can be altered to create a very wide range of previously unknown materials, by doping of glasses and ceramics with practically each of the millions of organic and bio-organic molecules known today. That development was made possible by the utilization of a room temperature procedure for the preparation of glasses and other ceramics known as the "sol-gel" process. It involves a polymerization reaction (rather then the classical melting technology) in the presence of the host molecule and results in a porous material which has the chemical composition of glass, looks like glass (it is transparent), and behaves like glass. Hence, we have termed our invention "Doped Sol-Gel Glasses".
Demonstrated Applications
As a consequence of the wide scope of the invention it touches upon many domains of modern needs. Following are some of the demonstrated applications of the new technology accumulated over a decade of research at The Hebrew University, and by many research groups, worldwide, who followed in our footsteps. These applications can be divided into three major areas: Applications which involve chemical reactions and interactions; applications which involve optical uses; and applications involving biochemical, clinical, and health-oriented products.
Applications in the area of chemically reactive doped sol-gel glasses include:
* Novel electrodes for various electrochemical reactions.
* Catalysts for synthesis of chemicals.
* Light-sensitive materials, for a variety of photochemical reactions.
Applications in the area of optics include:
* Filters.
* Laser components.
* Light-guides.
* Photochromic glasses (glasses which change their color upon the action of the light).
* Luminescent and phosphorescent materials.
* Optical memory and other memory recording .
Bio-applications include:
* Bioactive materials (prepared by doping the sol-gel glasses with enzymes and antibodies) for use as medical sensors (for instance, determination of glucose in diabetes), and as sensors for environmental pollutants.
* Bioactive materials for applications in biotechnology.
* Entrapment of food colorings, cosmetic components, and other ingredients in touch with the body.
(a) The sol-gel matrix is transparent to the UV range above 250 nm, allowing most types of optics applications
(b) The sol-gel matrix is thermally and photochemically stable, easily withstanding the normal duration of exposure to sunlight, and much beyond it.
(c) The preparation of the doped sol-gel material is simple: Direct physical entrapment in the course of the sol-gel polymerization is possible, and no reaction with the molecule itself is needed.
(d) The sol-gel method is not limited to the type of dopant - any molecule can be entrapped.
(e) The doped sol-gel particles can be down-sized to sub micron levels.
(f) The hydrophobicity/hydrophilicity ratio of the of the sol-gel particles' surface can be controlled by the suitable choice of the monomers (e.g., using trialkoxy derivatives).
(g) Likewise, the acidity/basicity of the particles can be controlled.
(h) The entrapped molecules are not in direct contact with external materials.
(i) Each doped molecule is isolated in an individual cage, thus avoiding ground state or photochemical interactions with impurities, photodecomposition products, adjacent molecules or other ingredients.
(j) The doped molecules have improved thermal and photochemical stability upon exposure to sunlight.
(k) As a consequence of (j), the shelf life of the doped sol-gel materials and of their preparations increases.
(l) Materials can be tailor either to no leaching of the entrapped molecule from the matrix, or to slow release.
(m) The oxides prepared for the sol-gel entrapment, such as silica, are non-allergenic and biocompatible.
(n) The entrapped molecule is by far more environmental friendly than the free molecule, allowing safe disposal.
(o) Compared to the use of surfaces of porous glasses on which molecules are attached, our technology offers much better protection of the organic molecules: molecules which are adsorbed on the surface are easily leached out; and molecules which are anchored on the surface, are prone to decomposition of the anchor; and both cases lack the protective action of the cage.
(p) Exceedingly high sensitivities of interactions can be obtained with our glasses. Thus, iron in drinking water is detected at a level of 100 parts per trillion (which is about 100 times more sensitive then existing methods). This property is achieved because of the dual action of the glass: it acts as a concentrator (for instance, of iron) because of its very high surface area; and then it performs the detecting reactions.
(q) In addition to the unique advantages of the sol-gel technology, it also shares with the plastics
technology all the advantages of the latter: it is a low-temperature polymerization process; the product can be obtained in any form (plates, discs, powders, thin films, etc.); it can be attached to most other materials (to plastics, paper, metals, etc.); it can be polished to optical quality; and, last but not least, it is cheap.
It is in order to mention that the properties of glass are a "package deal," which besides the inherent advantages over plastics, carries also the disadvantage of brittleness. However, we and many other laboratories have demonstrated that with the use of suitable additives, brittleness can be reduced dramatically.
The main message is that the chemistry and physics of organic molecules are carryable within ceramic matrices, allowing a plethora of novel and classical applications, and providing new insight on properties of both the organic component and of the matrix itself.