Ultra-thin MoS 2 nanosheets were treated by nitrogen (N 2) plasma to mediate the photo-reduction deposition of silver forming N/Ag@MoS 2 nanozymes for the catalysis-based colorimetric assay of hydrogen sulfide (H 2 S) in aquaculture water. [Display omitted] • MoS 2 nanosheets were treated by N 2 plasma to mediate the robust deposition of silver. • Enhanced electron transferring of N/Ag@MoS 2 can be achieved. • The deposited silver can act as a specific probe to recognize H 2 S. • N/Ag@MoS 2 can present the enhanced catalysis for the colorimetric analysis of H 2 S. • N 2 plasma treatment route promises the design of various nanozymes with 2D structures. Ultra-thin MoS 2 nanosheets were treated by nitrogen (N 2) plasma to mediate the photo-reduction deposition of silver forming N/Ag@MoS 2 nanozymes for the catalysis-based colorimetric assay of hydrogen sulfide (H 2 S) in aquaculture water. It was found that the as-produced N/Ag@MoS 2 could display a greatly enhanced peroxidase-like catalytic activity than that of MoS 2 nanosheets (about three times higher). Also, in the presence of H 2 S, a strong Ag-S interaction could occur to form non-conductive Ag 2 S onto N/Ag@MoS 2 nanocomposites towards the rationally reduced catalysis depending on H 2 S concentrations. Herein, on the one hand, the plasma treatment-aided doping of N elements into MoS 2 nanosheets might facilitate the robust deposition of silver onto MoS 2 nanosheets through the strong Ag-N chelation, and the enhanced internal electron transferring of N/Ag@MoS 2 nanozymes. On the other hand, the so deposited silver could not only enhance the catalytic properties of nanozymes, but also act as a specific probe for recognizing H 2 S to trigger the decreased catalysis of nanozymes. Importantly, such a N 2 plasma treatment pathway that mediates the deposition of silver onto two-dimensional structures like MoS 2 nanosheets may pave the way toward the design of various nanozymes for the analysis of different targets in the biomedical, food, and environmental monitoring fields. [ABSTRACT FROM AUTHOR]