Ultraefficient OG-Mediated Photodynamic Inactivation Mechanism for Ablation of Bacteria and Biofilms in Water Augmented by Potassium Iodide under Blue Light Irradiation

While photodynamic inactivation (PDI) has emerged as a novel sterilization strategy for drinking water treatment that recently attracted tremendous attention, its efficiency needs to be further improved. In this study, we aimed to clarify the ultraefficient mechanism by which potassium iodide (KI) potentiates octyl gallate (OG)-mediated PDI against bacteria and biofilms in water. When OG (0.15 mM) and bacteria were exposed to blue light (BL, 420 nm, 210 mW/cm²), complete sterilization (>7.5 Log cfu/mL of killing) was achieved by the addition of KI (250 mM) within only 5 min (63.9 J/cm²). In addition, at lower doses of OG (0.1 mM) with KI (100 mM), the biofilm was completely eradicated within 10 min (127.8 J/cm²). The KI-potentiated mechanism involves in situ rapid photogeneration of a multitude of reactive oxygen species, especially hydroxyl radicals (^•OH), reactive iodine species, and new photocytocidal substances (quinone) by multiple photochemical pathways, which led to the destruction of cell membranes and membrane proteins, the cleavage of genomic DNA and extracellular DNA within biofilms, and the degradation of QS signaling molecules. This multitarget synergistic strategy provided new insights into the development of an environmentally friendly, safe, and ultraefficient photodynamic drinking water sterilization technology.