Residue-free and reusable photodynamic inactivation of foodborne pathogens using a cationic magnetic nano-photosensitizer: An initial exploration in a liquid food system.

A cationic magnetic nano-photosensitizer (CMNP) was developed by co-condensing silanized chlorin e6 and quaternary ammonium groups onto silica-coated iron oxide nanoparticles. CMNP exhibited excellent colloidal stability, strong photodynamic activity, and enhanced bacterial affinity due to its high surface charge. Under 660 nm irradiation (30 J/cm), CMNP achieved 3.87-6.00 log reductions of Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus, and Listeria monocytogenes in purified drinking water. In clarified apple juice, despite reduced bacterial binding, 2.14-5.17 log reductions were still obtained at 90 J/cm. CMNP enabled complete magnetic removal, leaving no detectable residue and causing minimal impact on juice quality. Cytotoxicity assays confirmed that treated juice exhibited no additional toxicity to HepG2 and b.End3 cells. Moreover, CMNP maintained stable bactericidal efficacy over five reuse cycles. This study demonstrates a residue-free, recyclable photodynamic inactivation strategy and represents the first application of cationic nano-photosensitizers for microbial control in a liquid food system.