Phloxine B-loaded polymersomes enable eradication of Pseudomonas aeruginosa and Staphylococcus aureus in antimicrobial photodynamic therapy†

Utilised for decades in cancer therapy, the application of photosensitisers in antimicrobial photodynamic therapy is now well explored. In a smart wound dressing, an externally triggered antimicrobial strategy would enable on-demand infection eradication. Hence, in this work, the light-initiated production of reactive oxygen species from photosensitiser-loaded nanocarriers was explored. Such systems enable highly localised delivery of photosensitiser, without associated “dark toxicity” effects. The amphiphilic block copolymer PEG-block-PLA was synthesised via ring-opening polymerisation in the melt. Via the solvent shift method, the polymer was self-assembled into nanosized vesicles encapsulating Phloxine B, a commercial water-soluble photosensitiser. In vitro bacteria experiments with Phloxine B-loaded vesicles relied on localised illumination with green light (530 nm, 4 mW cm⁻², 15 minutes) to generate ¹O₂, killing the bacterial cells. A 6.8 log₁₀ reduction in CFU mL⁻¹ for Staphylococcus aureus and a 4.7 log₁₀ reduction in CFU mL⁻¹ for Pseudomonas aeruginosa are reported. Incorporation of these vesicles into a support matrix in combination with a reporter dye could provide a pathway towards promising smart wound dressings.