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

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 (1.33x10(-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.