Precise probe design based ESIPT coupled AIE mechanism toward endogenous cyanide in food detection and bioimaging

Abstract

Cyanide (CN–) is one of the strongest and fastest-acting toxic substances, and its excessive presence will cause great harm to the environment, food and human health. Although several fluorescent probes that recognize CN– have been extensively reported, developing the fluorescent probe with aggregation-induced emission (AIE) and large Stokes shift is still an extremely difficult problem due to lack of effective strategies. Thus, continuing efforts to seek novel, structurally distinct and functionally specific structures with large Stokes shift and AIE features are highly anticipated. Herein, we design and synthesize a novel asymmetric bis-Schiff base block (named as HPBC) based on the excited state intramolecular proton transfer (ESIPT) and AIE mechanism. Benefiting from restriction of intramolecular rotation and –CN electron-withdraw nature promoting the ESIPT effect of HPBC in the recognition system, HPBC shows large Stokes shift (243 nm), high selectivity, rapid identification of CN– and AIE effects. Excitingly, the limit of detection (LOD) was calculated to be 1.32 × 10-7 M, which was much lower than the 1.9 × 10-6 M specified by the World Health Organization and better than other previously reported probes. More importantly, further investigations demonstrated that the molecule we designed was successfully applied to sense endogenous CN– in food samples and the low cytotoxicity of HPBC was allowed to discover CN– in C. elegans, mice and HeLa cells. Overall, this work provides a new viewpoint of the rational design and synthesis of fluorescent probe toward CN– with AIE and large Stokes shift features, and triggers the discovery of new functions and properties of biological materials, which would open a new frontier for probes.