Selective and sensitive detection of cysteine in water and live cells using a coumarin–Cu2+ fluorescent ensemble

Abstract

Effective discrimination of cysteine (Cys) from biothiols and other amino acids has gained increasing attention due to the essential roles of this molecule in biological systems. In this work, we report a new strategy for the detection of Cys in aqueous media and live cells using a simple Cu²⁺ ensemble (L–Cu²⁺). A coumarin–salicylaldehyde hydrazone fluorescent ligand (L) was initially synthesized and well characterized. L features high affinity towards Cu²⁺ (K_a = 1.995 × 10⁶ M⁻¹), accompanied by effective quenching of fluorescence in HEPES buffer. The in situ generated chemosensing ensemble, L–Cu²⁺, is able to specifically respond to Cys over other biothiols and amino acids through a displacement approach. As a result, a remarkable recovery of fluorescence and UV-vis absorption spectra can be observed. L–Cu²⁺ showed high selectivity and sensitivity towards Cys. The detection limit is estimated to be 15 nM. Using L–Cu²⁺ as the fluorescent probe, imaging of Cys in live A549 cells was successfully demonstrated.