Antimicrobial peptide coating of TiO2 nanoparticles for boosted antimicrobial effects

This study explores coating of photocatalytic nanoparticles with antimicrobial peptides (AMPs) for boosted antimicrobial effects, and how such effects depend on AMP properties. For this, TiO2 nanoparticles were coated with the AMP KYE21 or its hydrophobically enhanced variant WWWKYE21. Mirroring effects of the free peptides, coated nanoparticles displayed higher binding and UV-induced degradation for bacteria-like than for mammalian-like membranes. In addition, they degraded bacterial lipopolysaccharides (LPS). Among the peptides, WWWKYE21-coated nanoparticles displayed higher nanoparticle binding to both LPS and bacteria-like membranes, as well as photocatalytic degradation, although saturation effects were found at high nanoparticle binding. Elucidating structural aspects, neutron reflectometry showed that binding of peptide-coated nanoparticles to bacteria-like membranes resulted in partial lipid removal also in the absence of UV, but that UV illumination caused additional layer degradation, demonstrated by increases in the hydration of both headgroup and acyl chain regions. For LPS, UV illumination induced removal of its outer O-antigen region. Analogous to these findings in model systems, antimicrobial effects of the peptide-coated nanoparticles against Escherichia coli bacteria on illumination were pronounced, while toxicity against human monocytes remained low. Taken together, the results show that AMP coating allows boosting of antimicrobial effects of photocatalytic nanoparticles without causing cell toxicity.