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.