“One stone, five birds”: Ultrabright and multifaceted carbon dots for precise cell imaging and glutathione detection

Developing a single system capable of realizing bacterial Gram-type identification, fungal cell imaging, endoplasmic reticulum (ER) imaging, glutathione (GSH) detection, and normal/cancer cell discrimination with excellent performance is a huge challenge. Herein, ultrabright green-emitting endoplasmic reticulum-targeting sulfur-doped carbon dots (SCDs) with a quantum yield of ∼ 78 % were synthesized via the hydrothermal treatment of rose bengal (RB) and dl-cysteine (Cys). The obtained SCDs possessed excellent fluorescence stability, unique excitation-independent emission property, and satisfactory biocompatibility. We demonstrated that the SCDs could be used for fast (15 min) identification of Gram-positive bacteria due to their S-containing groups (e.g., sulfate and sulfydryl groups) and high-quality fungal cell imaging. We also demonstrated that the SCDs could realize selective and long-term ER imaging in normal/cancer cells, and achieve the monitoring of the cell behaviors during ER stress caused by starvation or various ER stress inducers in live cells. Further, by mixing SCDs and Cu2+, we prepared Cu/SCD nanocomposites (Cu/SCDs), in which the fluorescence of SCDs was quenched by Cu2+ and could recover upon the addition of GSH, realizing GSH detection with a limit of detection of 0.681 μM. Subsequently, based on the much higher GSH level of cancer cells than that of normal cells, Cu/SCDs were successfully applied for distinguishing normal cells from cancer ones. Overall, this work fabricates ultrabright and multifaceted SCDs for precise and high-quality cell imaging and GSH detection, confirming the great potential of SCDs for versatile biomedical applications.