Fluorescent discrimination of cysteine, homocysteine, and glutathione in urine samples using a novel seleno-BODIPY probe

Biothiols, such as cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), play crucial roles in various physiological processes and serve as biomarkers for oxidative stress and redox homeostasis. Their structural similarities, however, pose significant challenges in selective detection and quantification, limiting the availability of suitable probes. Here, we report the design and synthesis of a novel ratiometric fluorescent sensor based on a seleno-BODIPY (Se-BODIPY) derivative, enabling rapid discrimination and quantification of Cys, Hcy, and GSH with low detection limits (Cys = 0.8 μM, Hcy = 20.4 μM, and GSH = 35.9 μM) via fluorescence. The probe exhibits high selectivity towards these biothiols over 11 amino acids, operating through dual-mode detection (absorption and emission spectra) with a visible color change from blue to orange (Cys/Hcy) or pink (GSH) in a turn-on fluorescence process. Notably, the distinct reaction mechanisms between Se-BODIPY and GSH versus Cys/Hcy lead to a more prominent blue shift for Cys/Hcy, facilitating their differentiation. Kinetic studies further differentiate Cys from Hcy, with the BODIPY reacting much faster with Cys than the latter. The effectiveness of the sensor was demonstrated in quantifying biothiols in urine samples, providing a non-invasive method with high recovery rates. Additionally, its incorporation into paper strips allows detection of biothiols in water samples via visible and UV light-induced color changes, indicating its potential for solid-state detection without organic solvents.