The adsorption properties of NH3 gas molecules on hydrogenated and fluorinated germanene nanosheet were investigated through density functional theory (DFT) method. From the observations of adsorption energy, Mulliken charge transfer, energy gap and average energy gap variation, the adsorption of NH3 on germanene nanosheet were explored and favorable adsorption sites were identified. The findings of the work clearly suggests that monolayer of hydrogenated/fluorinated germanene nanosheet can be used to detect the presence of NH3 gas. Moreover, the substitution of Al in germanene nanosheet enhances the adsorption properties of NH3 gas on hydrogenated/fluorinated germanene nanosheet. (C) 2016 Elsevier B.V. All rights reserved.