Taking advantage of the special nucleophilicity of cyanide, a new ratiometric fluorescent and colorimetric probe (Coum-1) was designed by tuning the π–conjugated bridge to affect the intramolecular charge transfer efficiency. Upon the addition of CN– anion, the probe displayed very large blue-shift in both fluorescence (90 nm) and absorption (90 nm) spectra, with the detection limit of 800 nM. Other anions gave nearly no interference. Furthermore, Coum-1 was successfully applied to the fluorescent microscopic imaging for the detection of CN– in HeLa cells.Keywords: cell imaging; cyanide; intramolecular charge transfer; probe; ratiometric fluorescent; reaction-based;