A coumarin-connected carboxylic indolinium sensor for cyanide detection in absolute aqueous medium and its application in biological cell imaging

Abstract Fluorescent sensor has been noticed in detecting system due to its sensitive, selective, operational simplicity and low cost. We designed a coumarin-connected carboxylic indolium sensor molecule that is water-soluble and cytomembrane-permeable. This infrared (IR) emitter is selectively sensitive towards cyanide detection in aqueous media according to CN− nucleophilic attack on the indole C=N function. Upon the addition of CN− anion, the color of sensor in water varied from blue to colorless by naked eyes and fluorescence quenching was observed by spectroscopic method. This was because the intramolecular charge transfer (ICT) effect occurred when the fluorescent sensor was added with CN−. The minimum detection limit of the sensor's fluorescence response to CN− is 4.44 × 10−7 mol/L. Furthermore, the cytotoxicity test shows the sensor has lower cytotoxicity, and indicates that this sensor can be utilized for practical detection of trace cyanide in wastewater.