Mercury ion （Hg2＋） pollution exists in water, soil, and food. By interacting with the thiol groups in protein, Hg2＋ ions can ac- cumulate in ways that cause serious damage to the central nervous system and threaten human health and natural environment. Undoubtedly, Hg2＋ ion detection is a significant issue in environment and health monitoring. A variety of sensor platforms for Hg2＋ ion detection based on organic molecules, DNA, oligonucleotides, inorganic materials, etc, have been reported. In this paper, an artificial peptide PHg, with a cluster bio-mineralize sequence （CCY） and a multi-charge hydrophilic sequence is de- signed as a template for the one-step synthesis of a peptide-Au cluster probe. Briefly： the peptide PHg in situ anchors Au ions to form a peptide-Au （I） intermediate and the reaction pH with NaOH is adjusted; alter 12 h incubation at room temperature, the peptide PGg-Au nanocluster probe with red fluorescence is obtained. The probe has a super-small core size of approximately 1.26 nm and a maximum emission peak at 650 rim. The presence of Hg2＋ ions cause the fluorescence of the probe to greatly decrease. Based on the differences in fluorescence intensity of the PHg-Au nanocluster in the absence and presence of Hg2＋ ions, Hg2＋ ions could be quantitatively detected in concentrations ranging from 5 nmol/L to 1 lamol/L. The limit of detection （LOD） is 7.5 nmol/L. Compared with some interference ions such as, K＋, Mg2＋, Ca2＋, Pb2＋, Ni2＋, Fe3＋, and Cue＋, the selectivity was excellent. The sensing of Hg2＋ ion is not affected by the chelate agents： EDTA, which imparts a significant advantage in a range of applications. As a result, a simple, sensitive and oped for the detection of Hg2＋ ions. selective fluorescent assay based on peptide PHg-Au cluster is devel-
