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Two-dimensional ultrathin tin monosulfide (SnS) nanoflakes have shown promise for gas-sensing applications thanks to their excellent lattice elasticity and superior anti-oxidation beyond black phosphorus. However when operating at room temperature (RT), both their gas-sensing response and detection limit are extremely subject to their low surface adsorption activity. In this work, the Mn atom with a local magnetic moment was selected to dope into the SnS lattice to boost the surface adsorption activation by introducing magnetic dipole inducement. The Mn-substituted SnS (Mn–SnS) showed unique hierarchical nanoflowers featuring nanoflake-assembled deep pores. On the grounds of this distinctive architecture and the doping-promotion effect, a fabricated Mn–SnS sensor exhibited a 3.35 times enhancement in response to 25 ppm acetone and much faster recovery characteristic in comparison to pure SnS, with a low detection limit of 500 ppb at RT. Based on adsorption fitting with the Langmuir isothermal model and calculations of the Gibbs free energy and electronic structure, the sensitive capability of Mn–SnS toward rarefied acetone and the enhanced response performances were demonstrated to originate from the physico-chemical synchronous adsorption of monolayer acetone molecules, as well as from the strong p–d orbital hybridization between the adsorbed acetone and Mn atom. Further, the rapid desorption characteristic of the acetone molecule on the Mn–SnS surface is the first-ever presumed based on DFT calculations and fitting equations by proposing a springback effect of the Mn atom in the Mn–SnS monolayer.