Synthesis of novel photoactive nanoparticles towards phototherapy
Nanomaterial-based compounds are attracting a lot of interest because many functionalities such as photoactive units, drugs and targeting groups can be combined on one platform to fight against infectious diseases and cancer. Recently, conjugated polymer-based nanomaterials have proven to be effective photosensitizers for antibacterial and photodynamic cancer therapies owing to their unique electronic and optical properties, including high singlet oxygen generation capacity, strong light-harvesting ability and its tunable optical spectrum. In this study, novel cross-linked conjugated polymer nanoparticles-based photosensitizers namely conjugated polymer-porphyrin nanoparticles (CPPN) and cross-linked conjugated polymer nanoparticles (PCP) were synthesized. The nanoparticles were prepared via nanoprecipitation using cucurbituril-(CB6)-catalyzed azide-alkyne cycloaddition (CB6-AAC) reaction. Conjugated polymer-porphyrin nanoparticles (CPPN) are advantageous than micelles incorporating porphyrin systems. For micelles containing porphyrin systems, the phototherapy effect of the porphyrin can only be seen after the porphyrin is released by conditions such as a change in pH, which is not the case for conjugated polymer-porphyrin nanoparticles (CPPN). The nanoparticles demonstrated high reactive oxygen species (ROS) generation efficiency which is evident in the antibacterial and anticancer photodynamic therapy (PDT) experiments. From the antibacterial photodynamic therapy experiment, when Gram-negative (Escherichia coli, E. coli) and Gram-positive (Bacillus subtilis, B. Subtilis and Staphylococcus aureus, S. aureus) bacteria were incubated with CPPN (20 µg/mL) and irradiated with white light (22 mW/cm2) for 10 min, more than 3.5-log reduction in colony-forming units (CFUs) was recorded for CPPN. Furthermore, when E. coli and B. subtilis were treated with PCP (24 µg/mL) and illuminated with light, about 3-log killing efficiency was recorded. However, in the dark, the nanoparticles demonstrated minimal dark cytotoxicity against the model bacteria. In addition, the anticancer photodynamic effect of CPPN and PCP on MCF-7 breast cancer cells was investigated. When MCF-7 breast cancer cells were treated with PCP in the dark and under light irradiation, almost all cells were alive for both cases. It may be that PCP could not generate enough reactive oxygen species to kill the cells. When MCF-7 breast cancer cells were treated with CPPN in the dark, the cell viability was 96% and upon irradiation with light for 20 minutes, the cell viability decreased to about 4%. Moreover, conjugated polymer-porphyrin-gold nanoparticles (CPPN-Au) and cross-linked conjugated polymer-gold nanoparticles (PCP-Au) nanoparticles were prepared, but due to the instability of the nanoparticles, they could not be used in phototherapy.