P,N,S‐Co‐Doped Red‐Emissive Carbon Dots for Microenvironment‐Sensitive Organelle Imaging and Monitoring Cellular Redox Processes

ABSTRACT

Red‐emissive carbon dots (R‐CDs) with reversible redox responsiveness and microenvironment‐sensitive imaging remain largely unexplored. Herein, phosphorus‐, nitrogen‐, and sulfur‐co‐doped red‐emissive carbon dots (PNS‐R‐CDs) were synthesized via a facile hydrothermal strategy using o‐phenylenediamine, sulfanilic acid, and phosphoric acid for reversible hypochlorite/glutathione (ClO ⁻ /GSH) sensing and intracellular bioimaging. The multifunctional surface‐engineered nanodots exhibited strong red emission at 605 nm with a quantum yield of 24% and pH‐dependent switching from red to greenish‐yellow emission, originating from heteroatom‐induced modulation of surface emissive states within a defect‐rich graphitic framework. The PNS‐R‐CDs exhibited a sequential redox‐responsive fluorescence switching behavior, in which fluorescence was quenched by ClO ⁻ and subsequently restored upon GSH addition, with low detection limits (0.182 µ

for ClO ⁻ and 0.205 µ for GSH), high selectivity, and excellent performance in both solution‐ and solid‐state platforms. Mechanistic studies revealed a radical‐mediated surface oxidation–reduction process governing fluorescence modulation. Importantly, PNS‐R‐CDs exhibited low cytotoxicity and enabled excitation‐dependent dual‐channel organelle‐specific imaging in HeLa cells, showing distinct fluorescence localization within RNA‐rich nucleolar domains and nuclear regions. This work establishes triple heteroatom‐doped red‐emissive CDs as multifunctional nanoprobes for spatially resolved redox sensing and microenvironment‐responsive bioimaging. The developed platform may further provide opportunities for adaptive oxidative stress imaging and intelligent fluorescence‐guided bioanalytical applications.