The identification of CN- in water, seeds, and biological systems has, because of its high toxicity, attracted the increasing attention of many chemical industry researchers. In the work, a novel highly selective and reversible sensor, MMY, was shown to recognize CN- effectively. The color and fluorescent changes verified the interaction of MMY with CN-, and the fluorescence lifetime of MMY was also changed upon addition of CN-. A mode of interaction of MMY with CN- based on the results of various experiments was speculated. The LOD of MMY toward CN- was 9.4 x 10(-10) M, lower than the concentration of CN- deemed acceptable by the WHO (World Health Organization) and the U.S. EPA (United States Environmental Protection Agency). MMY showed good reversibility and reusability for detecting CN-. In addition, test slips and silica plates were both earned by ourselves, which were able to recognize CN- qualitatively. Additionally, MMY could recognize CN- in tap water quantitatively with the use of a smartphone APP. Interestingly, MMY was also used to detect CN- in seeds. It was valid to image CN- in Caenorhabdit elegans and mice with a vivid "turn-on" fluorescence. MMY thus can circulate in the bloodstream.