Tertiary amines convert O to HO with enhanced photodynamic antibacterial efficiency.

Photodynamic inactivation (PDI) is a promising approach to combat the increasing global multi-drug resistance crisis. However, the very short half-life of O and the inevitable photobleaching of photosensitizer (PS) are the inherent drawbacks that largely compromise its therapeutic efficiency. Here, we report a ROS conversion strategy that simultaneously addresses these issues. Based on a photodynamic model system where riboflavin (RF) served as the PS, we have clearly shown that about 93.2% of O could be converted to hydrogen peroxide (HO) in the presence of tertiary amine. The less reactivity of HO (v.s.O) could retard the photobleaching of riboflavin by 88.9%. Orders of magnitude extended half-life of ROS (HOv.s.O) and retarded photobleaching of RF synergistically provide a more persistent oxidization that increased the oxidation capacity of the photodynamic model system by 56.6%. Consequently, it is able to improve the therapeutic efficiencies from 89.6% to 99.1% in combating methicillinresistant S. aureus (MRSA) and from 64.0% to 92.0% in eradicating S. aureus biofilm on biomaterials within a 5-min simulated sunlight illumination. The reinforced photodynamic model system could also significantly accelerate the healing & maturing of MRSA infected skin wound as compared to that of clinically used vancomycin. The generality of "ROS conversion" among different amines and different photosensitizers have been verified. These findings may inspire many creative approaches to increase the antibacterial efficiency of current photodynamic treatments for diverse applications.