Preparation and antibacterial ability of photodynamic antibacterial nanoparticles with ammonium cationic groups

With the increasing infection of drug-resistant bacteria, it has become a great challenge for researchers to find new approaches to eradicate drug-resistant bacteria and their biofilms. Photodynamic antimicrobial chemotherapy (PACT) is an indispensable part of the new anti-bacterial strategy because of its unique anti-bacterial mechanism, which can effectively inactivate drug-resistant bacteria without inducing further drug resistance. In this work, nanoparticles with N-isopropylacrylamide and methacryloxyethyltrimethyl ammonium chloride as monomers, and loaded with a fluorescent conjugated polymer were successfully prepared by microemulsion polymerization. The average particle size ranged from 100 to 200 nm. The nanoparticles could disperse in water steadily according to their zeta potential analysis. The nanoparticles generated singlet oxygen upon exposing to light with wavelength of 500–700 nm. Their PACT efficiency was investigated against Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus respectively. The results indicated that the antibacterial ability of nanparticles were excellent as the concentration was more than 0.01 mg/mL and the illumination time was 30 min. When the mass concentration of the nanoparticles was equal to or more than 0.05 mg/mL, the antibacterial mechanism was dominated by cation action, and when the concentration was equal or lower than 0.01 mg/mL, the antibacterial ability of the nanoparticles was improved effectively by photodynamic action. The antibacterial rate of the nanoparticle solutions against the bacteria in the biofilm was quantitatively studied, and it was proved that the nanoparticles eliminated bacteria in the biofilm effectively with a nanoparticle concentration of 0.2 mg/mL or more. The results indicated that the nanoparticles could effectively penetrate the biofilm to kill bacteria inside the biofilm by light illumination.