Green synthesis of fluorescent carbon dots from ascorbic acid and their application in sensing and biological imaging

A simple, highly efficient, and environmentally friendly one-step method has been developed to synthesize fluorescent carbon dots (CDs) with the assistance of hydrogen peroxide (H2O2). Here H2O2 acts as a green accelerator to promote the preparation of CDs, while temperature plays a critical role in controlling the entire synthesis process. The prepared CDs demonstrate monodispersion, with an average diameter of ∼6.8 nm, superior stability, and excitation-dependent photoluminescent (PL) behavior. The PL mechanism of the CDs was investigated using time-resolved PL decay, revealing that the PL originates from both the defect state and the intrinsic state of the CDs. Furthermore, the CDs show significant promise as pH sensors and versatile nanothermometry devices, owing to their remarkable sensitivity to both pH and temperature, as demonstrated by the pronounced dependence of their steady-state fluorescence emission spectra. It’s worth noting that temperature and pH sensors present significant reversibility, sensitivity, and linearity. More importantly, the CDs display low cytotoxicity, good biocompatibility, and the ability to enter human breast cancer Bcap-37 cells, making them highly suitable candidates for cellular imaging and labeling.