A new label-free method for the detection of Ag+ was developed.The G-rich DNA sequences with many C loop residues can be folded into quadruplex structures with thioflavin T（ThT） as inducer,but this quadruplex structure can be destroyed by Ag+ ions,thus a novel label-free biosensor was designed based on this principle.A detection limit as low as 60 nmol/L and a wide dynamatic range of 0.1-10 μmol/L were achieved in this assay.The method was applied in the detection of silver ions in samples from Xiangjiang water and tap water with satisfactory results.In view of these advantages,the developed method was expected to provide an intrinsically robust,highly sensitive and specific sensing platform for the analysis of Ag+ in complex system.