Modified gold nanoparticles modulated fluorescence and singlet oxygen generation of pheophorbide a as an effective platform for photodynamic therapy against Staphylococcus aureus

Gold nanorods coated with PEG or SiO₂ and mixed with pheophorbide a are bactericidal. The efficiency of singlet oxygen generation varied depends on the type of PEG polymer used for coating nanorods. The most effective against bacteria are the mixtures of PEG-coated nanorods with pheophorbide a, exposed to irradiation, which provides a >5.8 log reduction in the bacterial growth.

Abstract

The paper reports on the synthesis and evaluation of photochemical properties of gold nanorods (Au−NRs) coated with PEG with a thiol (−SH) group or SiO₂ and their physical mixtures with pheophorbide a. Also biological activity of these systems was tested in photodynamic therapy directed towards Staphylococcus aureus. The potential additive effect between differently functionalized Au−NRs and the dye pheophorbide a was also studied. The efficiency of singlet oxygen generation varied considerably depending on the type of PEG polymer used for coating NRs and was the highest, of 65%, for the polymer PEG (10k) and the Au−NRs concentration of (1.33×10⁻¹¹ M). For the other studied PEGs (2k, 5k) and the same concentration of NRs, a decrease in the singlet oxygen generation efficiency was observed. The most effective against Gram-positive bacteria were the mixtures of PEG-coated Au−NRs with pheophorbide a, exposed to irradiation at 405 nm and 660 nm, which provided a >5.8 log reduction in the bacteria growth. However, no strong bactericidal effect was noted in the case of irradiation with 525 nm.

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