Synthesis of nitrogen-doped citric acid carbon dots and their applications in chitosan-based antimicrobial coatings for blueberry preservation.

Carbon dots (CDs) used in antimicrobial coatings for postharvest fruit preservation are often limited by insufficient surface functional groups, which can be enhanced by heteroatom doping. In this study, nitrogen-doped citric acid carbon dots (NCA-CDs) were synthesized via a hydrothermal method and incorporated into a chitosan-based coating for blueberry preservation. The NCA-CDs exhibited uniform spherical morphology (1.86 ± 0.23 nm) with abundant functional groups (-OH, -COOH, -NH), conferring excellent bioactivity. The NCA-CDs/CS film showed a DPPH· radical scavenging rate of 81.62 ± 0.23% and exhibited significant antimicrobial activity against Escherichia coli and Staphylococcus aureus. Blueberry storage tests demonstrated effective suppression of microbial growth, extending shelf life to 10 days. Moreover, the NCA-CDs/CS coating exhibited negligible toxicity and good biocompatibility. This work provides a promising strategy for applying NCA-CDs-based nanomaterials in postharvest fruit preservation.