Low-cost sensors developed on paper by line patterning with graphite and polyaniline coating with supercritical CO2

Low-cost sensors were developed in two steps: (i) using a negative template to print graphite electrodes on vellum paper and (ii) coating with conductive polymers. Thin films of polyaniline (PANI) in the emeraldine oxidation state were investigated as active layers, after being synthesized by two routes: (a) polyaniline doped with dodecylbenzenesulfonic acid (DBSA) deposited by supercritical fluid (SC CO2) and (b) PANI doped with hydrochloric acid (HCl) by the in situ polymerization method. The electrical response (mV) was measured with dedicated circuitry, both in static laboratory air and with a flow of dry nitrogen gas (N2) at room pressure and temperature in a closed chamber, to assess the sensors for their sensitivity and reversibility. The phase morphology (microfiber structure) was characterized by FE-SEM. Results showed a difference in behavior between the sensors obtained by SC CO2 coating with PANI and by in situ polymerization. The voltage in the SC CO2 sensor decreased when it was exposed to the flow of dry nitrogen, whereas the opposite effect was observed in the other sensor.