In this study, a highly sensitive electrochemical sensor was developed for the detection of mercury ions in wastewater samples. The sensor was constructed using MoS₂/Au heterojunction nanostructures, which involved depositing plasmonic Au nanoparticles onto MoS₂ nanosheets on screen-printed carbon electrodes. The MoS₂/Au-SPCE sensor demonstrated outstanding electrochemical sensing capabilities, attributed to the emergence of a mid-gap state across the Fermi level. This state arises from the interaction between the Au 5d (Au, +1 charge state) and Mo 3d (MoS₂, +4 charge state) orbitals. This performance was superior to that of single Au nanoparticles and MoS₂. The sensor showed high sensitivity in detecting Hg(II) ions with a wide linear range from 0.02 ppm to 0.0004 ppb and a LOD of 0.0004 ppb. The developed sensor was effectively applied for the detection of Hg(II) ions in factory wastewater and other samples. The MoS₂/Au-SPCE sensor was successfully used to detect low concentrations of 565.0 ppb and 92.0 ppb Hg(II) in the investigated samples. This study introduces a new electrochemical sensor, leveraging the MoS₂/Au heterostructures, meticulously crafted for the intricate sensing of Hg(II) ions