Fibre-optic evanescent sensing of gaseous ammonia with two forms of a new near-infrared dye in comparison to phenol red

We report the evanescent detection of gaseous ammonia using the methylated and ethylated forms of a new dye and comparing their performance to that of the indicator dye phenol red. The two forms of the new dye were developed to produce spectral changes in the near-infrared region of the spectrum. Each of the dyes have been immobilised into the cladding material of commercial available plastic-clad silica (PCS) fibre. The response to gaseous ammonia was maximum at 565 nm for phenol red and 735 and 744 nm for the methylated and ethylated forms of the copper complex, respectively, and the calibration curves for the three dyes investigated exhibit a dynamic range of three orders of magnitude. Although all sensing fibres showed reversible responses to ammonia, the responses times were slow and need improving. The effect of atmospheric moisture on the copper complex methylated form was found to be negligible in the range of 0–50%RH.