Multifunctional near-infrared fluorescent probe for sensing of lysine and Cu2+/Fe3+ and relay detection of biothiols.

Lysine (Lys), Cu²⁺ and Fe³⁺ ions and biothiols are essential to a myriad of biological and pathological pathways, and their dysregulation is implicated in a variety of diseases. Development of fluorescent probes capable of detecting multiple analytes may be of great significance for early and accurate diagnosis of diseases and remains a huge challenge. In this context, a novel coumarin-dicyanoisophorone-based probe, engineered for the concurrent sensing of Lys, Cu²⁺, Fe³⁺ and biothiols was developed. The probe exhibited turn-on response to Lys, colorimetric and turn-off response to Cu²⁺ by formation of the probe-Cu²⁺ complex, and ratiometric sensing of Fe³⁺. In addition, the probe-Cu²⁺ complex served colorimetric and fluorescence turn-on sensor for biothiols. The limit of detection (LOD) values for the analytes were in the range of 0.30-4.40 μM. Sensing mechanisms based on intramolecular charge transfer (ICT) and iron-mediated hydrolysis of Schiff base were proposed and substantiated through density functional theory (DFT) calculations. Application of the probe for living cell bioimaging was demonstrated.