Evanescent sensing of alkaline and acidic vapours using a plastic clad silica fibre doped with poly( o-methoxyaniline)

We report a simple methodology for the immobilisation of an electrochromic conducting polymer, namely poly( o-methoxyaniline), in the cladding material of a plastic clad silica (PCS) fibre. Two modified optical fibres were prepared, one with the non-conductive emeraldine base form of the polyaniline derivative and one with its conductive form protonated with camphorsulfonic acid. Both fibres were tested for the evanescent detection of gaseous ammonia and HCl. The modified fibres were sensitive to 50,000 ppm ammonia and 1000 ppm HCl over a broad range of wavelengths in the near-infrared (NIR) region, where transmission loss is minimal in PCS fibres. The response times on exposure to ammonia and HCl were typically 80 and 50 s for the fibre modified with the undoped conducting polymer and significantly longer for the second modified fibre. Although the response of the modified fibres to such levels of chemical vapours was not reversible in ambient air we concluded that electrochromic conducting polymers are promising for distributed optical fibre chemical sensing applications.