The ratiometric fluorescence chemodosimeter N-butyl-4-(prop-1-en-1-yloxy)-1,8-naphthalic anhydride (NT-VE) was designed for Hg²⁺ recognition by oxymercuration at ambient temperature with high selectivity and no interference from other metal cations such as Cu²⁺, Ag⁺, Au³⁺, Fe³⁺, etc. The NT-VE could be incorporated into sodium dodecyl-benzenesulfonate (SDBS) micelles, which was confirmed by the clear emission enhancement observed in 0.1 mM SDBS. The hydrophobic core of the SDBS enhanced the solubility of NT-VE, enabling the detection of Hg²⁺ in aqueous solution, and the negatively charged micelle surface increased the local concentration of Hg²⁺ for amplified sensitivity. This work demonstrated the excellent performance of the NT-VE chemodosimeter for ratiometric detection of Hg²⁺ in aqueous solution. The NT-VE/SDBS system could detect Hg²⁺ over a linear range of 0.05–10 μM and a detection limit of 9 ppb (45 nM) in water.