Fig. 5

Mechanism investigation of PpIX and C14-EDTA in antimicrobial. a Flow cytometry analysis of the ROS levels in S. aureus after different treatments. The bacteria suspension was incubated with PpIX (17.77 μM) or its combination with EDTA or C14-EDTA for 1 h, the DCFH-DA probe for 15 min, and then irradiated for 30 min. b–c Percentage b and mean fluorescence intensity c of ROS-positive cells in panel a. d ROS detection generated by PpIX (17.77 μM) or its combinations in aqueous solution in the absence of bacteria. DCFH-DA was added into each well and incubated for 15 min. After illumination for 30 min, the fluorescence intensity was detected by spectrophotometer. e–f Size distribution measured by DLS e and SEM images f of PpIX or its combinations after 1-h incubation (PpIX:17.77 μM, EDTA/C14-EDTA: 0.05 mM). g, h PpIX accumulation in S. aureus in terms of counts g or intensity h. Bacterium suspension was pre-incubated with PpIX (17.77 μM) or its combination with EDTA or C14-EDTA for 1 h, followed by 1 h illumination. The accumulation percentage was then measured by flow cytometry (Ex: 488 nm; Em: 525 nm). Data are presented as mean ± SD (n = 3). ****P < 0.0001, ***P < 0.001, **P < 0.01