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Enhanced light-target interaction using a novel anti-resonant waveguide concept


In optical biosensors the interaction between light and target molecules is typically very weak. In order to improve this interaction we have developed a novel anti-resonant waveguide concept, in which the core region has a lower refractive index than the cladding layers. With this concept the light can be guided within the target-containing medium, thereby enabling an extended interaction length. An anti-resonant waveguide is especially compatible with a fluidic biosensor because the fluidic channel itself can be used as the core of the anti-resonant waveguide. In a traditional optical waveguide the light is confined by total internal reflection inside of a high index layer surrounded by regions of low refractive index. In these cladding layers, which are used in many conventional biosensors, only the evanescent field of the electromagnetic wave is affected by absorption, fluorescence or refractive index changes. In an anti-resonant waveguide the light is guided within the analyte-containing layer and most of the light intensity can be used for sensing or excitation. We have tested this anti-resonant waveguide approach by demonstrating large area fluorescence excitation. By coupling the excitation light from the appropriate angle of incidence into a liquid film between two glass slides we are able to excite fluorescence within the whole film (e.g., an area of 25x75mm2). The measured fluorescence intensity per unit area was equal to that obtained by focusing the total excitation power onto a small spot (e.g., 3x3mm2).

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Schmidt, O. ; Bassler, M. ; Kiesel, P. ; Wolst, O. H. ; Doehler, G. Enhanced light-target interaction using a novel anti-resonant waveguide concept. Optical Diagnostics and Sensing VI; 2006 January 25; San Jose CA. SPIE Proceedings vol. 6094: 6094F.


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