Prolonged exposure of ammonia results in many potential health hazards for humans as it interacts immediately upon contact with available moisture in the eyes, skin, oral cavity, respiratory tract and particularly mucous surfaces, thereby, causes cellular destruction and tissue necrosis. In this paper, we report a detailed comparison between ammonia gas sensing, spectral, structural, and morphological properties of the dodecyl benzene sulphonic acid doped polyaniline (PANI-DBSA) nanostructures synthesized using a template free direct route using surfactant dopants as structure directing agents and using indirect route. Two different samples of PANI-DBSA nanostructures have been prepared via template free direct route (Nanostructured DBSA doped PANI has been prepared by emulsion polymerization of aniline in the presence of DBSA) and indirect doping route (Nanostructured DBSA doped PANI has been prepared via chemical oxidative polymerization of aniline monomer). Different characterizations revealed that the spectral, structural, morphological, and ammonia gas sensing properties of the synthesized PANI-DBSA nanostructures are highly dependent on the synthesis route. Thin film of nanostructured PANI-DBSA prepared using template free direct route exhibited better ammonia gas sensing response (7.97) as compared to thin film of nanostructured PANI-DBSA prepared using indirect doping (3.24) due to availability of large number of grain boundaries and higher doping levels. © 2019 IEEE.