| 摘要 |
The present invention provides methods and apparatus for inexpensively and accurately sensing with the use of a fiber optic guide the presence or absence of a particular substance ("analyte"). The preferred embodiment of the sensor of the present invention comprises a light source, a photodetector, and a loop shaped plastic fiber that is exposed to the environment and that acts as a sensing element. In the preferred embodiment, the fiber optic guide comprises a core and a cladding, either of which are coated with a coating that is selected to at least partially degrade in the presence of the analyte. The coating is selected to have an index of refraction below that of the core but sufficiently large to allow at least some light to escape from the core even in the absence of the analyte. A decrease in the amount of light is detected when the analyte is present. Alternatively, the coating is selected to have an index of refraction just above or greater than the core, causing an increase in the amount of light that is detected when the analyte is present.
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