KI-potentiated antimicrobial photodynamic activity of new carboxyalkylthio-substituted chlorins against Escherichia coli

ABSTRACT: Antimicrobial photodynamic therapy (aPDT) is a promising approach for bacterial inactivation based on the light activation of photosensitizers (PSs) and the subsequent generation of reactive oxygen species. In this study, three fluorinated carboxyalkylthio-substituted chlorins (H 2 Chls 1 – 3 ) were investigated for their photophysical properties and photodynamic activity against bioluminescent Escherichia coli , used as a Gram-negative bacterial model. H 2 Chls 1 – 3 showed absorption in the visible region and were able to generate singlet oxygen upon irradiation. The antimicrobial photodynamic activity of H 2 Chls 1 – 3 was evaluated at 1.0 and 2.5 μM, either alone or in combination with KI (100 mM), under broad-spectrum white-light irradiation (400–800 nm, 50 mW cm -2 ) for up to 90 min. Under the experimental conditions investigated, H 2 Chls 1–3 alone did not produce significant reductions in bacterial bioluminescence compared with the corresponding controls. In contrast, the addition of KI markedly potentiated the photodynamic response. At 2.5 μM, all three H 2 Chl/KI systems reached the detection limit after only 5 min of irradiation, corresponding to a light fluence of 15 J cm -2 . These results demonstrate the important role of KI in enhancing the photodynamic performance of H 2 Chls 1 – 3 against E. coli and support further investigation of these carboxyalkylthio-substituted chlorins as photosensitiser platforms for KI-potentiated aPDT.