The current study involved the development of a new optical sensing system that utilizes a fluorescent probe DTT to detect Hg(II) ions in nanomolar levels. The synthesized probe 5-((4-(dimethylamino)benzylidene)amino)-1,3,4-thiadiazole-2-thiol (DTT) exhibits weak fluorescence due to the photoinduced electron transfer (PET) process. The emission of the DTT probe was seen to be enhanced during the titration reaction with Hg(II) ions. This enhancement can be attributed to forming a 1:1 complex between DTT and the Hg(II) ions that inhibit the PET process and cause chelation-enhanced fluorescence (CHEF). The system's fluorescence intensity was not significantly affected by other metal ions, such as alkali, alkaline metal ions, and some transition metal ions, demonstrating its exceptional selectivity. Job's plot and Benesi-Hildebrand-based fluorescence method were applied to confirm 1:1 binding stoichiometry between DTT and Hg(II) ions and calculate the binding constant value of 2.26 x 105 M-1, respectively. Determining the limit of detection (LOD) and limit of quantification (LOQ) yielded values of 21 nM and 70 nM, respectively. With its exceptional selectivity and ultra-sensitivity, as seen by its exceptionally low detection limit, The sensing efficiency towards Hg(II) was examined with a dynamic range of 0.070 to 1 μM, even in the presence of other metal ions, demonstrating its high degree of selectivity. The system was rendered reversible by employing an EDTA solution with a concentration of 1 µM. Additionally, the DTT probe exhibits potential as an optical chemical for detecting Hg(II) ions in environmental samples.