A new class of nitrobenzoic acid-based AIE photosensitizers for highly efficient photodynamic antibacterial therapy

Photodynamic therapy (PDT) has been drawing more and more attention in the antibacterial field. Traditional photosensitizers (PSs) tend to aggregate in aqueous media, which reduces the generation of reactive oxygen species (ROS) and seriously affects the photodynamic efficacy. Many efforts have been made to prevent aggregation of traditional PSs. By contrast, aggregation-induced emission PSs (AIE-PSs) take advantage of aggregation to boost ROS generation and fluorescence intensity. However, the efficacies of the reported antibacterial AIE-PSs are poor. Herein, we report a new class of highly effective antibacterial AIE-PSs based on nitrobenzoic acid structure. TTVBA, a negatively charged AIE-PS, can not only selectively kill spherical bacteria (Staphylococcus aureus (S. aureus)) rather than rod-shaped bacteria (Escherichia coli (E. coli)), but also be easily extended to several AIE-PSs (TTVBP1-3) with positive charges and broad-spectrum antibacterial activity. We demonstrate that TTVBP2 can kill 3.0 log10 of S. aureus at very low concentration (125 nmol L−1), TTVBP3 can kill 4.7 log10 of Staphylococcus epidermidis (S. epidermidis) at a concentration of 1 µmol L−1 and 3.8 log10 of E. coli at 5 µmol L−1, thus enabling them among the most effective antibacterial AIE-PSs reported so far. Meanwhile, these AIE-PSs exhibit excellent wash-free imaging ability for bacteria by simple mixing with bacteria. We thus envision that TTVBA, a nitrobenzoic acid-based extendable AIE PS, provides a new route for the design of AIE-PSs in antibacterial treatment.