Cinnamomum burmannii waste-derived carbon dots as a novel photosensitizer for effective photodynamic inactivation of foodborne Escherichia coli.

With the increasing threat of foodborne diseases, photodynamic inactivation (PDI) has attracted attention as a non-thermal sterilization technology that preserves food quality. But the efficiency of photosensitizers (PSs) is limited by short lifespan and limited diffusion distance of reactive oxygen species (ROS). Therefore, it is necessary to develop PSs capable of penetrating cell membranes and directly generating ROS within cells to effectively inactivate foodborne microorganisms. Among emerging materials, carbon dots (CDs) are small, water soluble, exhibit low photobleaching rates, and possess a core-shell structure with abundant surface functional groups, making them promising candidates for PDI. In this study, functional carbon dots (M-CDs) were synthesized from Cinnamomum burmannii waste. The M-CDs demonstrated strong fluorescence, excellent water solubility, and surface groups such as carboxyl and hydroxyl, which enhanced their biocompatibility and antimicrobial activity. With a diameter of approximately 3.355 nm, M-CDs efficiently penetrated cell membranes to generate ROS directly within cells, thereby inactivating foodborne microorganisms via multiple targets. The PDI efficacy of M-CDs against Escherichia coli 8739 was evaluated, demonstrating that 50 mg/L M-CDs reduced bacterial counts by 3.8 log10, and 200 mg/L achieved complete bacterial eradication. Transcriptome analysis revealed gene enrichment in pathways related to lipid metabolism, energy metabolism, DNA repair, and oxidative stress responses. Moreover, M-CDs effectively reduced microbial contamination in Psidium guajava (guavas) and extended their shelf life by eight days at room temperature. The findings of this study provide new insights for developing green, safe, and effective strategies to control foodborne pathogen.