Green Synthesis of Carbon Quantum Dots from <i>Gardenia Jasminoides</i> for the Selective Detection of Fe³⁺ Ions and Cell Imaging

The selective and sensitive detection of Fe³⁺ is of significant importance in environmental monitoring and biomedical applications due to its vital yet potentially toxic roles in biological systems. Herein, we report a fluorescent sensing platform based on carbon quantum dots (CQDs) synthesized from <i>Gardenia jasminoides</i> via a facile, eco-friendly hydrothermal method. The as-synthesized CQDs feature an average particle size of 2.76 nm, strong blue fluorescence with an emission peak at 435 nm, and a moderate quantum yield of 13.7%. Notably, the CQDs exhibit excellent selectivity and sensitivity for Fe³⁺, along with robust stability over a broad pH range (2-10), under high ionic strength, in the presence of H₂O₂, and upon prolonged oxidative stress. Cytotoxicity assays reveal concentration-dependent behavior: high biosafety up to 500 μg/mL, yet significant antiproliferative activity against tumor cells above this threshold. Cellular imaging of A549 cells shows strong, dose-dependent cytoplasmic fluorescence at 1000 and 2000 μg/mL. These combined properties establish the <i>Gardenia</i>-derived CQDs as promising candidates for trace Fe³⁺ detection and high-contrast bioimaging.