Manipulating Donor–Acceptor Interactions in AIE Photosensitizers for Targeted Tracking and Photodynamic Killing of Viable Gram-Positive Bacteria via Metabolic Labeling

The timely detection-control of spoilage bacteria and foodborne pathogens is critical in food industry and food safety. Although several methods have been reported for either the discrimination or the inactivation of viable bacteria individually, studies that integrate both functions into a single rapid platform remain scarce. Herein, a bifunctional fluorescent bioimaging-photodynamic sterilization strategy toward viable Gram-positive bacteria was proposed and validated, with merits of high efficiency and no drug resistance. Importantly, a sequence of bacteria-metabolizable AIE-d-ala photosensitizers with enhanced donor–acceptor effect and unique d-alanine labeling were rationally designed and synthesized for turn-on bioimaging as well as in situ photodynamic ablation of food-related bacteria. Once metabolically incorporated into bacterial peptidoglycan, the intramolecular motions of AIE-d-ala are inhibited, enabling clear fluorescence visualization and enhanced photodynamic bacteria inactivation. Evaluation of structure–function relationships reveals that strong electron-withdrawing groups can obviously strengthen the fluorescent signals and increase the generation of reactive oxygen species. Under white-light illumination, our AIE-d-ala (0.5 μM) inactivated 100% Lactobacillus acidophilus and 99% Staphylococcus aureus, much more efficient than the commonly used photosensitizer curcumin. Meanwhile, it effectively retarded pork spoilage. This work provides a new route to design high-performance AIE-active photosensitizers with strong targeting capability toward viable Gram-positive bacteria.