Photodynamic inactivation of Staphylococcus aureus and Escherichia coli with free-base and indium(III) 5,10,15,20-tetrakis(4-pyridyl) porphyrin adsorbed onto single-walled carbon nanotubes

The emergence of resistance against antimicrobial agents by bacteria is a challenge that calls for the development of new antimicrobial technologies. In this study, 5,10,15,20-tetrakis(4-pyridyl) porphyrin (1) and In (III) 5,10,15,20-tetrakis(4-pyridyl) porphyrin (2) conjugated with single-walled carbon nanotubes (SWCNTs), 1-SWCNTs and 2-SWCNTs, respectively, were used to study the photodynamic inactivation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Time-dependent density functional theory (TD-DFT) was used to establish the relationship between structural modifications to the porphyrin core and the resultant bathochromic shift and increase of the Q bands. Introducing a central metal resulted in a blue-shifted spectrum of 2 and more stable MO energies. Additionally, the photosensitizer’s photophysical characteristics were determined. 1-SWCNTs and 2-SWCNTs appear to be more photostable than 1 and 2 due to the single-walled carbon nanotubes. The singlet oxygen quantum yields of 2-SWCNTs and 2 were 0.74 and 0.68, respectively which was higher than that of 1-SWCNTs (0.61). 2-SWCNTs showed the highest log reduction against both E. coli (8.38) and S. aureus (9.76). Both 1-SWCNTs and 2-SWCNTs showed significant photodynamic activity. Hence, they can be recommended as efficient photosensitizers in aPDI.