Hg2+-Mediated Ratiometric Fluorescent Carbon Dots for Imaging Glutathione in Living Cells and Zebrafish

Glutathione (GSH), a cancer-related biomarker in cells, has numerous important roles in maintaining intracellular homeostasis; hence, rapid detection and imaging of GSH are essential in physiological and pathological processes. However, because other biological thiols, such as cysteine (Cys) and homocysteine (Hcy), are very similar in structure and properties to GSH, it remains a challenge to distinguish GSH from Cys and Hcy, particularly in vivo. Herein, a novel ratiometric fluorescent probe (NSCDs@Hg2+) was designed to discriminate GSH from Cys/Hcy. Nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using a hydrothermal method of neutral red and 4-aminobenzenesulfonic acid. The specific interaction between Hg2+ and NSCDs can induce NSCDs nanoparticle aggregation, while the high-affinity binding of GSH and Hg2+ can reverse the process from the aggregation to dispersion state. As a result, as-prepared NSCDs can be developed as optical dual-mode and smartphone imaging platforms for ratiometric detection and visual quantification of Hg2+ and GSH. Highly desirable attributes of the probe, such as good biocompatibility and low cytotoxicity, allow for cancer cell recognition. Importantly, the probe was also applied to specifically detect GSH in living cells and zebrafish.