CHEMICAL-VAPOR SENSING BY SURFACE-PLASMON RESONANCE OPTICAL-FIBER SENSOR COATED WITH FLUOROPOLYMER

A surface plasmon resonance fibre optic sensor has been developed allo wing sensitive remote detection. A 50 nm thick silver film is deposite d by thermal evaporation onto the silica core of the optical fibre. To protect silver from oxidation, self-assembled monolayers (SAM) of lon g-chain alkanethiols were used. For detecting gas and vapours, the sur rounding dielectric medium consists of a polymeric material deposited on the modified metallic film. Chlorinated and aromatic compounds have been tested with detection limits of 0.3%, 0.7%, 1% and 2% for trichl oroethylene, carbon tetrachloride, chloroform and methylene chloride, respectively, and 0.13%, 0.19% and 0.95% for xylene, toluene and benze ne, respectively. For aromatic compounds, the response of the sensor d epends on the boiling temperature, whereas for chlorinated compounds i t depends on the difference between the refractive index of the analyt e and specific polymeric cladding. Moreover, both the response time (a bout 2 min) and the desorption time (about 2.5 min) have been obtained with good reproducibility.