Low-cost fiber-optic waveguide sensor for the colorimetric detection of ammonia
We present the development and characterization of a low-cost fiber-optic colorimetric gas sensor for ammonia combined with the electronic circuitry for measurement control and RFID communication. The gas sensor detects ammonia using a 300 μm polyolefin fiber coated with a gas-sensitive polymer film. The spectral and time-dependent sensitivity of various polymer films was tested in transmission measurements at λ = 590 nm. A prototype of the gas sensor was tested under realistic measurement conditions, i.e. battery-driven and in a completely autonomous mode. The sensor system showed good sensitivity to the ammonia concentrations and response times in the order of minutes. The achievable power consumption was below 100 μW. Bromophenol blue-based films showed a strong reaction to ammonia, with saturation concentrations around 1,000 ppm and response times of about 15 s to 100 ppm. The colorimetric reaction was simulated using a simple kinetic model which was in good agreement with the experimental results.