As a kind of important water pollutant, heavy metal ions have a detrimental effect on the health of human. In this study, Au@Ag core-shell nanoparticles were synthesized by simple reduction of Ag + around Au nanoparticles and functionalized by DNAzyme. Based on thymine-Hg
2+-thymine binding mode, a sensitive aptamer biosensor was constructed by utilizing functionalized Au@Ag core-shell nanoparticles as labels, and the sensitivity was enhanced by DNAzyme due to the catalysis toward H 2 O 2 . Under optimal conditions, square wave voltammetry was carried out to measure the current derived from Au@Ag nanoparticles labels. The current response of biosensor increased with the increasing of Hg 2+ concentration, which presented linear relation in the range of 0.002-20 μg L -1 with limit of detection of 0.006 μg L -1 . Meanwhile, the electrochemical biosensor showed superior reversibility, stability, repeatability, and selectivity.