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Ammonia detection at ambient with low-cost sensors is a challenge for various applications like breath analysis and agriculture. Such a challenge can be reached with functionalized SnO2 based gas sensors using silanization by 3-aminopropyltriethoxysilane (APTES) as an intermediate step before grafting with functional end group providing selectivity for the target gas. Moreover, operation at room temperature gives the opportunity to develop a sensor on a plastic substrate entirely manufactured by inkjet technology, by developing suitable inks, in particular to obtain SnO2 sensing element.

Mixed potential ammonia gas sensors were fabricated by using two sensing materials of Ni3V2O8 and Au-V2O5 as working electrodes, YSZ as electrolyte and platinum as reference electrode. The results have shown that the Ni3V2O8 sensors show cross-sensitivity toward NO gas. However, Au-V2O5 working electrodes displayed a high sensitivity to NH3 as well as fast response and recovery times at high temperatures. Furthermore, the results indicate that the selectivity of Au-V2O5 sensors increases by increasing temperature.

In this work, a flexible tin oxide (SnO2) gas sensor was successfully fabricated by inkjet printing technology. This thin film deposition technique requires the formulation of stable suspensions with specific fluidic properties. Aqueous Sol-gel method was applied to synthesize a stable sol based on tin oxide, then transformed into ink with the appropriate viscosity and surface tension to be printed using a drop-on-demand piezoelectric inkjet printer. Thermal analyses of synthetized sol show that a crystallized structure of SnO2 could be obtained at 350 °C, which is lower than crystallization temperatures of SnO2 previously reported in the literature, and entirely consistent with our plastic substrate. The printed thin-film was then sintered at 350 °C on polyimide foil (Upilex-50S) and characterized as sensor.

The development of selective and cheap metal oxide gas sensor at ambient temperature is still a challenging idea. In this study, SnO2 surface functionalization was performed in order to obtain sensitive and selective gas sensor operated at ambient temperature. 3-aminopropyltriethoxysilane (APTES) was used as an intermediate step, followed by functionalization with molecules having acyl chloride with different end functional groups molecules such as alkyl, acid and ester groups. Acid and ester modified sensors are sensitive to ammonia between 0.2 and 10 ppm at room temperature. However, ester modified SnO2 is more selective than acid modified sensor regarding ethanol and carbon monoxide gases.

Among all NOx reduction approaches, selective catalyst reduction (SCR) system is one the most reliable ways to control NOx emissions from diesel engine vehicles and trucks. In order to optimize the conversion rates of NOx and to prevent inducing excessive NH3 to the air, an NH3 and NOx sensor is required. In this study, three different types of YSZ ink have been examined to identify the most effective electrolyte for NOx and NH3 sensing. The results have shown that a home-made ink with YSZ powder shows the best sensitivity towards ammonia without polarization and the highest NO2/NO signal ratio with polarization current of 25 nA.

Sol based SnO2 precursor was synthetized by aqueous sol-gel route, then transformed into a stable ink with appropriate viscosity and surface tension to be inkjet printed and sintered at relatively moderate temperature. Plastic foil with thickness of 50 μm was selected as substrate for its high thermal resistance and stability (Upilex-50S). Prepared sol and formulated ink were both characterized by analytical techniques; electrical measurements were performed on the printed sensing film to characterize the response to CO gas in different concentrations, at working temperature of 300 °C.