HIGH-SENSITIVITY GAS SENSORS BASED ON GAS-PERMEABLE LIQUID-CORE WAVE-GUIDES AND LONG-PATH ABSORBENCY DETECTION

A new fluoropolymer is proposed as the basis of a novel class of senso rs.' The devices are based on selective chromogenic reactions and in s itu long-path optical absorbance measurement. The polymer is transpare nt from 200 to 2000 nm and has the lowest known refractive index (RI) of any synthetic polymer. The RT is less than that of water, A tube of this material, filled with an aqueous solution (or virtually any othe r liquid), behaves as a liquid core optical fiber. As a result, long-p ath length optical cells are possible without significant loss of ligh t. The material is highly permeable to a number of trace gases of envi ronmental interest. Relative to common poly(tetrafluoroethylene) (PTFE )-type Teflon, the new amorphous fluoropolymer (Teflon AF 2400) is mor e than 3 orders of magnitude more permeable to many gases. If a Tenon AF tube is filled with a reagent that responds to a gaseous analyte by undergoing a change that is spectroscopically detectable, an unusuall y versatile, sensitive, and inexpensive gas sensor can be made with co nventional optical fibers at each end, connected respectively to an in expensive light source such as a light-emitting diode and a photodiode detector, A capillary hollow fiber structure allows a high surface-to -volume ratio, allowing high sensitivity, and supports a thin wall, wi th response times down to subsecond periods. The potential for similar sensors for volatile organic compounds dissolved in water is also dem onstrated.