Near-infrared reagents for fibre-optic ammonia sensors

Abstract Representatives of three types of near-infrared dyes, i.e., Cu(II) complex of 5-( N ′-diethylamino-phenylimino)quinoline-8-one (D1), NIR acid-base indicator 1,5-bis-[ p -dimethylamino-phenyl]-divinylene-carbenium-perchlorate (D2) and squaraine dye (D3), have been tested as reagents for fibre-optic ammonia sensors. Both D1 and D2 show reversible response to ammonia and are thus suitable for the monitoring of gas ammonia. D1 has low stability and hence cannot be easily incorporated into a polymer matrix or silica matrix prepared by the sol-gel method. D2 can be incorporated into the silica matrix. D3 is also sensitive to ammonia, but the sensitivity is solvent dependent and the response is irreversible.