Coffee shell-derived carbon dot-chlorogenic acid nanoparticles with enhanced aPDT antibacterial activity for fish preservation during cold storage

Chlorogenic acid-loaded coffee shell-derived carbon dot nanoparticles (CGA/CSCD NPs) with enhanced antibacterial photodynamic therapy (aPDT) activity were developed, exhibiting strong fluorescence (~400 nm), a graphite-like structure, and around 3 nm size. The nanoparticles achieved efficient ROS generation and bacterial enrichment, showing superior antibacterial efficacy and biocompatibility. Applied to Carassius auratus , Megalobrama amblycephala , and Dicentrarchus labrax under 4 °C storage, the CGA/CSCD NPs-aPDT treatment inhibited 99% of bacterial growth over 7 days, maintaining counts at 10 4 –10 5  CFU/g. The treatment significantly slowed pH rise, inhibited TVB-N accumulation, and reduced lipid oxidation by 2–3 times compared to controls. Furthermore, the nanoparticles preserved fish quality by minimizing moisture loss and maintaining color stability and texture (hardness and chewiness). These results demonstrate that CGA/CSCD NPs-aPDT provides a sustainable and effective strategy for delaying spoilage and extending the shelf life of aquatic products during cold storage.