An uncontrolled increase of the nitrite concentration in groundwater,rivers and lakes is a growing threat to public health and the environment.So it is extremely important to monitor the nitrite levels in drinking water and clinical diagnosis.Herein,we designed a novel fluorescence switch-off probe(PyI)for the sensitive detection of the nitrite ions in the aqueous medium by a simple and direct method.This probe selectively recognizes the nitrite ions through a distinct visual color change from colorless to pink with a detection limit of 36 nM.This method has been successfully applied to the determination of nitrites in tap water,lake and yellow river with recoveries in the range of 95.6%~104.3%.Furthermore,this probe can be used for the sensitive detection of the iodide ions further in the presence of nitrite ions with the detection limit of 334 nM.