Modulation of Backbone Charge in Polyfluorene Polyelectrolytes for Potent Antibacterial Application

The rapid rise of antibiotic-resistant bacteria poses a severe threat to human health and civilization. To combat the antibiotic resistance developed by pathogenic bacterial strains, an effective bactericidal material is urgently in demand. Here, cationic conjugated polyelectrolytes (CPEs) PFTMI and PFTPyMI were synthesized, one with exclusively cationic side chains and the other with a cationic backbone and cationic side chains, respectively. This cationic charge is responsible for effective binding with the bacterial membrane and hence killing by disrupting the membrane without the need for light or energy. PFTPyMI outperforms PFTMI in antibacterial activity, with minimum inhibitory concentrations (MIC) of 4 μg/mL for Escherichia coli (E. coli) and 32 μg/mL for Staphylococcus aureus (S. aureus) due to its cationic backbone enhancing the electrostatic attraction and hence killing efficiency. Further, the presence of bacteria in aqueous media can be easily detected from the fluorescence color change using a 365 nm portable UV lamp. Remarkably, both CPEs are lowly cytotoxic to normal HEK 293 cell lines and toxic to HeLa cells, which paves the way for exploration in real-time biomedical applications. Further CPEs are employed as an anticoating agent over a cotton pad, and the results are comparable to the commercially available antibiotic Kanamycin.