Quaternary ammonium salt-functionalized fluorescent probes: Integrating the functions of cysteine detection, mitochondrial targeting and antibacterial activity.

Abnormal cysteine (Cys) levels are implicated in the pathogenesis of cardiovascular diseases and metabolic disorders, with mitochondrial Cys perturbation being a critical indicator of redox imbalance and disease risk. Fluorescent probes have emerged as a key method for detecting Cys and a research hotspot in recent years. Current development trends are increasingly focusing on enhancing aqueous solubility and achieving multifunctionality. Herein, we report a series of cationic fluorescent probes engineered by integrating a quaternary ammonium-functionalized phthalimide fluorophore with a 2,4-dinitrofluorobenzene recognition moiety. Among these probes, CBTA exhibited high sensitivity and selectivity toward Cys, achieving a limit of detection of 2.25 × 10-7 M. Its practical utility was validated in real sample analyses, which yielded recovery rates of 94 %-110 % and confirmed its specificity. Mitochondrial colocalization experiments confirmed that CBTA exhibited effective mitochondrial targeting capability, with a Pearson's correlation coefficient of 0.79. All these quaternized probes demonstrated significant antibacterial activity, with NDTA achieving a remarkable 100 % inhibition rate. This study presents an integrated platform that synergistically combines fluorescent sensing, targeted imaging, and antibacterial functionality, holding potential applications in fluorescence detection and disease diagnosis and treatment.