A new colorimetric and fluorescent probe (QI) based on quinoline-indolium was developed for detection of CN À . In an aqueous solution, QI showed high selectivity and strong antiinterruption for CN À . In addition, it was clearly visible to the naked eyes that the color and fluorescence changes induced by CN À exhibited sharp contrast. The research also found that QI could determine CN À in the range of pH 5-10. The spectral signal was linearly proportional to CN À concentration, and the detection limit was calculated to be low as 41.6 nM. The sensing mechanism of QI to CN À was accomplished via the attachment of CN À at the C atom of indolium salt C=N + group through the nucleophilic addition, which was confirmed by 1 H NMR studies. Notably, we could apply the designed probe for the cycle detection of CN À in a wide pH range, for practical purposes for a long duration. Furthermore, the TLC plates of QI were verified to detect CN À in a simple, rapid way in environmental systems.