A sensor for colorimetric determination of silver and mercury ions based on G quadruplex-hemin DNAzymes was fabricated.The G quadruplex-hemin DNAzymes was formed by the combination of G quadruplex(5′ CTGGGAGGGAGGGAGGGA 3′) with hemin,which could catalyze H2O2 to oxide the substrate efficiently,and make the colorless solution become green.The presence of Ag+ or Hg2+ in the solution would hinder the formation of the DNAzyme,and the solution color became lighter.Under the optimal experimental conditions,there were good linear relationships for the absorbance of the solution with Ag+ and Hg2+ in the concentration ranges of 1000-1 0000 nmol/L and 800- 8000 nmol/L,with detection limits(3δ/Slope) of 559 nmol/L and 643 nmol/L,respectively.This method was of good selectivity,and was applied in the detection of real samples with satisfactory results.