A Cys-responsive fluorescent sensor for monitoring Cys levels in a polycystic ovary syndrome mouse model.

Polycystic ovary syndrome (PCOS) is a prevalent endocrine-metabolic disorder among women of reproductive age and is closely associated with oxidative stress, redox imbalance, and metabolic dysfunction. Accumulating evidence indicates that elevated cysteine (Cys) levels are involved in PCOS-related pathological processes and may reflect disease-associated metabolic alterations. Herein, we developed HD-Cys, a hemicyanine-based fluorescent molecular probe for sensitive detection of Cys. HD-Cys responds to Cys through a specific activation mechanism, generating a pronounced fluorescence enhancement with a low detection limit of 0.02 μM. Its biological applicability was investigated using cellular imaging, where HD-Cys enabled visualization of endogenous Cys-associated fluorescence changes. More importantly, serum analysis demonstrated that HD-Cys clearly differentiated PCOS-model samples from healthy controls, with markedly enhanced fluorescence signals consistent with elevated Cys levels under PCOS pathological conditions. Benefiting from its high chemical specificity, favorable stability, and good biocompatibility, HD-Cys provides a useful molecular tool for assessing Cys dysregulation in PCOS and holds potential for early disease evaluation and treatment-response monitoring.