Detection of gaseous ammonia at different concentrations is crucial for many industrial, environmental and medical purposes [1]. Behind its toxicity and its involvement in secondary aerosol formation [2], it can be used as a biomarker in non-invasive diagnosis tools based on the analysis of exhaled breath [3], [4]. Among sensitive materials dedicated to ammonia gas sensors, conductive polymers and more specifically polyaniline, present the advantages to be easily processed, selective and energy-efficient due to its low working temperature [5]. However, in order to respect applicative requirements, it is necessary to optimize performances of organic devices by (i) enhancing their sensitivity, (ii) ensuring the robustness of the measurement by limiting the impact of humidity and (iii) increasing their stability with time. Actually, we show how the composition of the material, the choice of the substrate and the process of deposition can be used to optimize ammonia sensors based on polyaniline doped with camphor sulfonic acid, composite well known for its ability to detect ammonia at low concentration (below 1 ppm) [6]. Firstly, the addition of polyurethane in doped polyaniline is presented as a good solution to limit the impact of humidity (Figure 1) and to increase the stability of the sensors. This argument is supported by a systematic study of polyaniline mixed with different concentrations of polyurethane using scanning electron microscopy, Raman spectroscopy, wettability analysis and detection measurement in various and controlled environments. Secondly, the quality of the substrate and the cleaning process before drop-casting are presented as simple leverage to enhance the sensitivity of the material. Finally, those results are analysed according the diversity of uses faced by ammonia sensors: monitoring of (i) ambient air quality, (ii) yield in microelectronic manufacture and (iii) exhaled breath for Chronic Kidney Disease diagnosis.