Fabrication of Polyaniline-based Ammonia Sensors on Plastic µ-Hotplates

Polyaniline (PANI) is known for its excellent ammonia sensing properties. However, due to the slow desorption of NH3 molecules from the sensing layer, PANI ammonia sensors often show poor reversibility. One strategy to enhance regeneration of these sensors after exposure to ammonia is to maintain the sensing layer at relatively higher temperatures than ambient in order to improve dissociation of analyte molecules and accelerate sensor recovery. Polymeric micro-hotplates have been developed to enable sensor operation at elevated temperatures with very low power consumption (~35 mW). The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes, separated by a thin patternable dielectric film. A sensing layer composed of polyaniline doped with poly(4-styrenesulfonic acid) (PSSA) was in-situ polymerised on the micro-hotplate’s sensing area, using vapour-phase deposition polymerisation (VDP) method. The resistive response of the sensors was measured over the concentration range of 250 ppb-3.65 ppm ammonia vapour in dry and humid air. When operated at 95 ºC, the PSSA-doped PANI sensors made by VDP, show sensitive, selective and reversible response to low concentrations of ammonia vapour. Such low-cost sensors can be employed in sensing applications where high sensitivity, fast recovery and low power consumption are required. (This work was supported by FlexSMELL-FP7-PEOPLE-ITN-2008-238454.)