Evanescent wave coupling, fiber optical

Modified fiber-optic-based sensors can be used for sensing pollutants, explosives, drugs, pharmaceuticals, and miscellaneous organics (Yeh et al. 2006). Optical fibers coated with porous silica can be used to detect the presence of chlorinated hydrocarbons. Alternatively, these compounds can also be detected using fiber-optic-coupled surface plasmon resonance methods. Aromatic compounds were detected by evanescent wave absorption spectroscopy. Suitably modified fiber-optic array tips can be used to detect presence of explosive materials (Wolfbeis 2000). 

An evanescent wave is generated in the space between the optical fiber and the outside lower refractive index material. Fluorescent molecules in this region can absorb energy from the evanescent wave and fluoresce. A portion of the fluorescence will be coupled back into the fiber and can be detected. By immobilizing antibodies to the surface of an optical fiber, fluorescent interference from the bulk solution is almost completely eliminated. The signal generated in the assay corresponds... 

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