ROS conversion promotes the bactericidal efficiency of Eosin Y based photodynamic therapy.

Photodynamic therapy (PDT) is becoming an efficient antibacterial strategy without drug-resistance. Here, we report a promising reactive oxygen species (ROS) conversion strategy to increase the antibacterial efficiency of an Eosin Y (EOS)-based PDT system. Based on visible-light illumination, EOS generates a high concentration of singlet oxygen (1O2) in the solution. With the introduction of HEPES in the EOS system, it can almost completely convert 1O2 to hydrogen peroxide (H2O2). The orders-of-magnitude increases in the half-lives of the ROS (H2O2vs.1O2) present in the solution can enable more persistent oxidation ability. Thus, it is able to increase the bactericidal efficiency (against S. aureus) from 37.9% to 99.9%, promote the inactivation efficiency of methicillin-resistant S. aureus (MRSA) from 26.9% to 99.4%, and enhance the eradication rate of MRSA biofilm from 69% to 90%. Further in vivo investigation showed that the increased oxidation ability of the EOS/HEPES PDT system can enable quicker healing and maturing (even better than that for vancomycin administration) of MRSA-infected skin wounds on rats. This strategy may find many creative applications for the efficient eradication of bacteria and other pathogenic microorganisms.