Photosensitizer-Conjugated Hollow ZnFe₂O₄ Nanoparticles for Antibacterial Near-Infrared Photodynamic Therapy

In this work, Ce6-mediated photodynamic therapy (PDT) was investigated for antibacterial inactivation, using ZnFe2O4–Ce6 nanocarriers operated with low-irradiance light in the near-infrared range. To fabricate ZnFe2O4–Ce6 nanocarriers, the highly purified photosensitizer was modified with polyethylenimine (PEI ) using a standard 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride–N-hydroxysuccinimide coupling reaction. Then, it was conjugated with hollow ZnFe2O4 nanospheres (NSs). The as-synthesized ZnFe2O4–Ce6 nanocarriers were found to have an average size of ∼100 nm, increased water solubility, high singlet oxygen generation capability, and broad light absorbance in the range of 400–800 nm. The chemical changes and surface charge confirmed the stable conjugation of PEI–Ce6 with hollow ZnFe2O4–Ce6 NSs. The ZnFe2O4–Ce6 nanocarriers (50 μg/mL) exhibited excellent antibacterial activities of >98% for every bacterial cell even under the low-irradiance light at 660 nm. Furthermore, the structural examinations revealed that Gram-negative Escherichia coli was more vulnerable than other Gram-positive cells to the nanocarrier-mediated PDT. This work may provide insights into a promising approach using photosensitizers in PDT for combating antibiotic-resistant bacteria.