Sensors for Volatile Chemicals: Room Temperature Ammonia and Humidity Sensing

There have been extensive studies on conducting polymers and their use as chemical sensors especially for detection of odours. Among them, polyaniline (PANI) stands out due to its higher environmental stability and lower price. PANI is known to be sensitive to ammonia because of the high affinity of protonated N atoms on doped-PANI backbone to NH3. However, due to its lack of solution processability it is difficult to fabricate thin films of PANI. We have developed a vapour-phase deposition polymerisation (VDP) technique to in situ polymerise a very thin Nafion-doped PANI sensing layer on the flexible substrate. The conductivity of the sensor is reduced on exposure to ammonia even in a humid environment. The sensor shows sensitive, rapid and reversible response to very low concentrations of ammonia vapour in the range of 250-1500 ppb at room temperature. Moreover, the sensor shows a reversible increase in conductivity upon increasing humidity. Hence, a low-cost and flexible sensor for ammonia and humidity detection at room temperature is realised using a VDP method which is compatible with common solution-deposition techniques. The sensor can be used in smart tags for monitoring of perishable goods during the transportation chain.