A bimetallic Cu-BHQT receptor for selective cysteine detection in extracellular environments via fluorescence quenching-recovery

Abstract

Aminothiols such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) are crucial biomolecules involved in numerous physiological processes. Cys has garnered particular interest due to its role in health and disease, with increased blood levels (>300 µM) linked to serious medical conditions. We prepared a novel fluorescent probe (BHQT) featuring a benzyl spacer connecting between quinoline and hydrazine units that served as a fluorophore and metal-chelating part. The fluorescence of BHQT was effectively quenched with Cu²⁺, forming a 1 : 2 ratio of complex, BHQT : Cu was confirmed by a Job's plot. Upon addition of Cys, the BHQT-Cu complex recovered fluorescence of BHQT by displacing Cu²⁺. The released Cu²⁺ subsequently formed a Cu-Cys complex. This sensing system showed a limit of detection of ∼419 µM, which is suitable for detecting increased Cys levels prior to pathological onset. This reversible sensing behaviour of BHQT allowed for specific recognition of Cu²⁺ and Cys, and demonstrates its potential as a sensitive tool for extracellular Cys monitoring and clinically relevant analyses. Overall, the BHQT probe offers a promising approach for selective Cys detection through Cu²⁺ coordination chemistry, combining sensitivity with practical applicability in biological and clinical contexts.