An indolium ion-based colorimetric sensor for naked-eye detection of cyanide and ammonia: on-site detection technique for cyanide in natural sources and day-to-day monitoring of food spoilage.

Herein, we developed an easy-to-synthesize, simple colorimetric probe and demonstrated its potential for the detection of anions and amines. The probe was capable of detecting CN^- selectively among other anions and could detect the presence of all tested amines. It exhibited obvious colour and spectroscopic changes in the presence of the said analytes. The probe was highly sensitive to CN^- ions, which enabled the detection of trace amounts of the aforementioned anion. The detection limit for CN^- was found to be 3.98 × 10^-8 M, which is below most of the LOD values reported thus far. The sensing was further extended to the solid state by effectively immobilizing the probe in a hydrogel matrix. Moreover, upon exposure to ammonia vapour, noticeable colour changes were observed in a probe-coated paper chip within few minutes. Moreover, the practical application of the probe was demonstrated for both CN^- and amines. The probe can serve as a promising alternative for detection of CN^- content in food and monitoring of biogenic amines and food freshness.