Fabrication of Novel Yellow-Fluorescent Carbon Dots and Their Application for Fe³⁺ Detection.

Sensitive, rapid, and cost-effective detection of Fe³⁺ is urgently required for biological research, food safety, and environmental monitoring. Herein, novel yellow-fluorescent carbon dots (CDs) were successfully synthesized via a facile one-step solvothermal method using ursolic acid and o-phenylenediamine as green precursors. The as-prepared CDs, with an average particle size of 4.82 nm, exhibit bright yellow fluorescence (λem = 540 nm) and high selectivity toward Fe³⁺. The fluorescence intensity is linearly quenched by Fe³⁺ in the range of 0-150 µmol/L, with a low detection limit of 0.096 µmol/L; meanwhile, the fluorescence lifetime remains unchanged, indicating a static quenching mechanism. The proposed sensor displays excellent stability and anti-interference performance, and has been successfully applied to Fe³⁺ detection in real spinach and lake water samples, with satisfactory recoveries of 98%-105%. This work provides a green and reliable fluorescent probe for Fe³⁺ analysis in food and environmental samples.