Preparation of Red-Emitting CDs for Glioma Imaging and Fe³⁺ Sensing

Red-emitting fluorescent carbon dots (CDs) have garnered significant attention due to their wide-ranging applications in biological fields. However, challenges such as complex precursors, labor-intensive preparation processes, and low quantum yields have hindered their broader utilization. In this study, we developed a simple and efficient solvothermal method to synthesize fluorescent CDs with tunable emission wavelengths using aniline derivatives as precursors. The emission wavelengths of the synthesized CDs were influenced by the functional groups at the para-position of the aniline derivatives with stronger electron-donating effects leading to a red shift in emissions. Notably, bright red-emitting CDs with a quantum yield of 19.42% and excellent photobleaching resistance were obtained by using p-phenylenediamine as the sole precursor. These CDs exhibited sensitivity to Fe³⁺ ions, demonstrating a strong linear detection range (R ² = 0.999) from 0 to 50 μM. Additionally, the CDs were uniform in size (2-5 nm), emitted stable red fluorescence in pH conditions ranging from 4 to 10, and were successfully internalized by glioma cells, enabling precise fluorescence imaging of gliomas both in vitro and in vivo.