A simple benzothiazole-based fluorescent probe (TDA) for the determination of Hg2+ ion in aqueous solutions was synthesised in one step and characterised by 1H NMR, 13C NMR, APT, COSY, FTIR, and elemental analysis. TDA shows a significant fluorescence change upon the interaction of Hg2+ ion in DMF-water (v/v = 1/1), while only minor changes in fluorescence intensity are observed with 18 other metal ions. Fluorescence enhancement by a factor of 15 is achieved upon selective interaction with Hg2+ ion. The Hg2+ ion detection process is found to be pH dependent; therefore, TDA could be feasible within a pH range of 4.0-7.0.