Design of new integrated optical substrates for immuno-analytical applications
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Integrated optical Mach-Zehnder interferometers supply information on changes in refractive index and/or thickness of a film placed as a superstrate on top of one of its surface wave-guides. The internal propagation of light is influenced by the evanescent field reaching into the superstrate. This propagating light interferes with an uninfluenced wave in the second arm after recombination. The result is an intensity modulation depending on the refractive index parameters of the substrate, the waveguide itself and the properties of the superstrate. Taking an antigen layer as the superstrate, its interaction with antibodies changes its thickness by several nanometers. This can be observed by recording the change in intensity of the signal of the interferometer. The sensitivity of such a device depends on particular values of the optical parameters of substrate and waveguide with respect to the given superstrate properties. Computer calculations help to select optimum glass and waveguide fabrication conditions. The numerical results of a variety of assumed conditions have been tested experimentally. The application to the improved detection of triazines is discussed.
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