An amplified fluorescence turn-on assay for mercury(II) detection and quantification was developed. This method makes use of specific thymine/mercury(II)/thymine coordination to capture Fl-labeled DNA onto NP surface. Addition of a cationic conjugated polymer leads to an amplified Fl signal in solution. A sigmoidal Hg2+ working curve is obtained at fixed [NP] with a detection limit of 0.1 x 10(-6) M. However, by reducing [Hg2+] and [NP] simultaneously, while maintaining [Hg2+]:[DNA duplex] = 3:1, a linear calibration curve is observed with a detection limit of 5 x 10(-9) M. The CCP-assisted mercury(II) assay shows potential applications in environmental mercury detection and for industrial process control.