Low-cost H2S gas sensor based on plastic optical fiber

A new fibre optic sensor for cumulative detection of H2S and other sulphide compounds, which is conceived for applications in cultural heritage preservation, is described. The transducer measures the total exposure to sulphide vapours exploiting a chemical non-reversible reaction that alters the evanescent field absorption. The sensor is fabricated by deposition of an Ag thin film by plasma sputtering on a plastic optical fiber. The substitution of plastic optical fibres for glass fibres accounts for the possibility of having all the advantages of a fibre-based device while improving the sensitivity to evanescent field sensing and lowering the cost of the final device. Some prototypes of sensors have been developed and tested in a climatic chamber in the presence of sulphide vapours: the light transmission exponentially decays with a time constant which depends on the sulphide partial pressure, obtaining a total loss of about 90% from the initial Ag film to a completely Ag2S layer. Comparative tests with a commercial sensor based on an electrochemical cell that operates in the amperometric mode have shown the high sensitivity of the proposed sensor which detects less than 0.1 ppm.