Smartphone-assisted dual-mode cyanide ion sensing in environmental and biological matrices using a triphenylamine-quinoline-conjugated chromogenic receptor.

This work presents the efficient recognition of the hazardous chemical cyanide ions (CN- ions) using a newly designed organic molecule-based fluorescent receptor, (E)-4-(4-(diphenylamino)styryl)-1-propylquinolin-1-ium (TAME). CN- ion detection occurs via nucleophilic addition to the styryl group, inducing distinct electronic perturbations as well as blocking of the intramolecular charge transfer (ICT) process. Absorption spectral titration studies reveal a notable blue shift (517-507 nm) in the presence of CN- ions, while steady-state fluorescence measurements demonstrate significant fluorescence quenching (∼82%) with a strong red shift from 553 nm to 576 nm following the interaction of CN- ions with the receptor TAME. The lowest limit of detection (LOD) for this fluorescence-based sensing strategy was calculated to be 1.48 nM, which is much lower than the WHO-permissible limit for cyanide in drinking water. Furthermore, the probe was successfully employed as a paper strip, enabling the portable and effective recognition of CN- ions. Additionally, this sensing system illustrates a notable colour-changing behaviour, which was further exploited for CN- ion detection through a smartphone-based RGB color variation analysis technique. The real-world utility of the receptor TAME was established through its ability for the effective quantification of hazardous CN- ions in various real water and food samples.