Porphyrin cross‐linked conjugated polymer nanoparticles‐based photosensitizer for antimicrobial and anticancer photodynamic therapies

We report here the synthesis and characterization of a water dispersible conjugated polymer nanoparticle-based photosensitizer and its application in the antibacterial and anticancer phototherapies. Nanoparticles (CPPN) were synthesized in one-pot by nanoprecipitation method, in which a hydrophobic azide functionalized, red-emitting thiophene-benzothiodiazole based conjugated polymer (CP-AZ) was cross-linked with a hydrophilic, propargylamine functionalized porphyrin (TPP-4AL) through cucurbit[6]uril (CB6) catalyzed azide-alkyne cycloaddition (CB6-AAC) reaction. CPPN demonstrated high stability in aqueous medium for more than a month without any visible aggregation and appeared to be a good photosensitizer with high light-triggered reactive oxygen species (ROS) generation ability. Consequently, CPPN displayed photo-induced biocidal activity against Gram-negative (Escherichia coli, E. coli) and Gram-positive (Bacillus subtilis, B. subtilis and Staphylococcus aureus, S. aureus) bacteria. When bacteria suspension was incubated with CPPN (20 μg ml−1) and irradiated with white light (22 mW cm−2) for 10 min, more than 3.5-log reduction in colony-forming units (CFUs) was recorded for the three model bacteria. CPPN demonstrated minimal dark cytotoxicity against the bacteria. Moreover, the cytotoxicity of CPPN on mammalian cell was studied using MCF-7 breast cancer cell line. The results demonstrated that CPPN is non-toxic to mammalian cells in the dark even at a high concentration of 112.5 μg ml−1 and this feature makes CPPN an ideal photosensitizer.