Conductive Polymer Based Ammonia Sensors:Fabrication,Properties And System Applications

Sensing or detection of ammonia?NH₃?has been widely used in environmental monitoring,medical diagnosis,and food quality inspection.In addition to the basic performance requirements including sensitivity,selectivity and detection range,these applications also require the sensors to be manufactured at low cost,and have compact systems for convenient use.Conductive polymers of different molecule structures have been intensively studied for gas sensing applications attributed to several advantages,including ease of functionalization for different types of sensing,excellent mechanical flexibility,compatibility with low cost solution based or printing processes and low temperature substrates.However,it is still a big challenge to fabricate high sensitivity NH₃ sensors using simple printing or coating processes with common conductive polymer materials.Based on the commercial poly?3,4-ethylene dioxythiophene?:poly?styrenesulfonate??PEDOT:PSS?aqueous solution,this thesis firstly studies using inkjet printed PEDOT:PSS line structures with surface morphology control and spin-coated PEDOT:PSS/silver nanowire?AgNW?composite films as the sensitive layers,respectively for fabricating flexible NH₃ sensors of improved sensitivity with simple and low cost processes.The mechanisms for the sensitivity improvement are analyzed.The results show that the inkjet-printed PEDOT:PSS sensors present obviously improved response with a small detection limit?less than50 ppb?compared to the spin-coated one.Compared to that of devices with smooth and straight lines,the responsivity of the devices fabricated at a drop spacing of 40?m is improved to nearly threefold.Under the condition of ammonia concentration of 25 ppm,the relative variation of resistance of the sensor with composite film can reach 40%,which is much larger than that of pure PEDOT:PSS devices?3%?.Then,the response properties upon NH₃ and relative humidity changes and mechanisms are studied for devices made of different PEDOT:PSS based films with adding dimethyl sulfoxide?DMSO? or AgNWs.Two types of PEDOT:PSS based flexible sensor devices are fabricated,which are sensitive to NH₃ and humidity,respectively.Further,based on the PEDOT:PSS based NH₃ sensor,a handheld system is implemented for pork freshness early inspection.Finally,by integrating the PEDOT:PSS based NH₃ and humidity sensors,and a near field communication?NFC?chip,a flexible multi-sensing system is obtained and attached on the package film of pork for inspecting the freshness of the meat without needs of opening the package using smart phones.The thisis provides solution processes to design and implement the PEDOT:PSS NH₃ sensor based on conducting polymer with high sensitivity and insensitive to the relative humidity change.The portable NH₃ system and the flexible NH₃/RH sensing system are implemented providing useful theoretical and technical foundations for meat freshness detection of conducting polymer gas sensors.