Solvent-Free Synthesis of Fluorescent Carbon Dots: An Ecofriendly Approach for the Bioimaging and Screening of Anticancer Activity via Caspase-Induced Apoptosis

Ecofriendly and highly fluorescent carbon dot nanoassemblies have gained prominence for their diverse biological applications, with a focus on combating environmental and human health problems. In this study, we prepared highly fluorescent nitrogen-doped carbon dots from the persimmon fruit (termed as "PCDs"), which was used as a carbon source, via a one-step hydrothermal reaction without any solvent. It is interesting to note that the as-prepared PCDs were highly water-soluble because of the numerous polar functional groups, such as hydroxyl (-OH), amine (-NH2), and carboxylic acid (-COOH) groups, as confirmed by ultraviolet-visible, Fourier-transform infrared, and X-ray photoelectron spectral analysis. These polar functional groups enabled the production of nanohybrids by immobilization of the anticancer drugs doxorubicin and gemcitabine on the surface of the PCDs (PCDs@Dox and PCDs@Gem, respectively) through the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide coupling reaction. Unlike other reports, as-prepared PCDs@Dox and PCDs@Gem nanohybrids were successfully employed for bioimaging and caspase-induced apoptosis applications. The neat PCDs exhibited significant pH-induced cytotoxicity because of the presence of surface carboxylic acid and phenolic moieties. Thus, PCDs@Dox and PCDs@Gem effectively inhibited the proliferation of HeLa cells in a dose-dependent manner, and the cytotoxicity of the nanohybrids in fibroblasts was significantly lower than that of cancerous cells at the same dose. In addition, it is quite certain that promising boi-imaging results were identified from PCDs like as conventional dyes, which may account for the synthesis of highfluorescent PCDs without using any solvent. The results demonstrate that the nanohybrids mediate the production of reactive oxygen species (ROS), and this mediation is followed by a decrease in the mitochondrial membrane potential through the activation of caspase-3. These results appear to be promising for anticancer drug delivery and bio-imaging engineering applications.