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Badania luminescencyjne w żelach silanowych

Miller E.

Wiadomości Chemiczne

2000

[Z] 54, 5-6

435-455

Recently, optical sensors (optodes) are very often applied in biomedical sciences and biotechnology in analytical methods which require high sensitivity, selectivity and accuracy. The methods consist in the transmission of analyzed radiation by means of an optical fibre from the source to the sensor, and then of the response from the sensor to the detector also in the form of a light signal at a changed wavelength. A chromophore indicator sensitive to changes in physicochemical properties of an analyzed substance that take place in the reaction system is immobilized on the surface of an optical waveguide. Advantages of the optodes include, among other things, no need to use a reference signal, a very small size and weight, elasticity, a possibility of using distant measurements (up to 1 km) a simple sensor construction and low price. These sensors can be used in the analysis of samples in both liquid and gas phase. This is why they found application in the environmental protection to analyze groundwater and flue gases, in toxicology and to test product quality in the food industry. If an enzyme which catalyzes an appropriate chemical reaction or a co-immobilized enzyme with a sensor transforming changes in the concentration of a substance being formed or decayed as a result of the enzymatic reaction, is immobilized on the fibre surface, then also biologically important compounds such as glucose, fructose, urea, lactate, amino acids, as well as pH can be determined. In the latest studies on the formation of optical materials, especially an organic chromophore immobilizer, researchers often use silane gel which is obtained by the sol-gel technique. In comparison to a high-temperature synthesis of silica glass, the advantage of preparing silane matrices by gelation is that the process requires very mild conditions. This is why an organic compound, e.g. a luminescence probe, introduced to the input sol is not degraded during the gelation process. This paper describes the process of silane gelation in the classical approach according to Flory-Stockmayer's theory and then using the percolation theory. Further on, methods of silane gel formation based on the latest studies are presented. Recent studies on the gelation process based on the excimer spectrum of a classical pyrene probe are discussed. Results of the studies, on the basis of which changes were observed in viscosity and polarity of the fluorophore microenvironment during gelation, are quoted. The changes were measured by the ratio of intensities of respective peaks in the pyrene emission spectrum or fluorescence anisotropy . This paper presents also results of the recent luminescence research of sol-gel transition dynamics using other chromophores, e.g. rhodamine G6, ruthenium complex ,oxazine, 1,4-dihydroxyanthraquinone, 3,3-diethyloxadicarbocyanines and quinine. The silane gel has properties which are important and interesting from the point of view of its application, i.e. transparency, porosity, thermal stability, and ability to form different carrier forms, e.g. powder, film or fibre. So, in the final part of this paper the examples of applications of these carriers in the newest probes, i.e. chemical optical sensors, biochemical optodes, and immunocolumns are presented.