REMOTE-SENSING OF TETRACHLOROETHENE WITH A MICRO-FIBER OPTICAL GAS SENSOR-BASED ON SURFACE-PLASMON RESONANCE SPECTROSCOPY

A miniaturized fibre optical sensor based on surface plasmon resonance spectroscopy is investigated in view of the detection of organic solv ent vapours, particularly tetrachloroethene. Surface plasmons are exci ted on a silver coated multimode fibre by polychromatic light, and the resonant excitation is detected as a resonant absorption band in the measured output spectrum. When the analyte is absorbed in a thin gas-s ensitive polysiloxane film deposited on the silver layer the polymer f ilm changes its thickness and its refractive index. These changes resu lt in a wavelength shift of the resonant curve depending on the analyt e gas concentration. Theoretical considerations about the sensing effe ct are made and resonance curves were computer-simulated. Based on the se simulations the layout of all sensor parameters was optimized. The sensor shows an excellent response to tetrachloroethene with a respons e time of two seconds and high reproducibility. When using self-assemb ling monolayers on the silver surface a long-term stability of more th an 3 months can be obtained. Very low cross sensitivities of less than 1% to other solvent vapours like acetone and ethanol are obtained, fu rthermore, the influence of humidity is very low. This miniaturized fi bre optical sensor in combination with an easy-to-handle and non-sophi sticated measuring and evaluation unit is excellently suitable for the remote sensing of special organic solvent vapours.