Photocatalytic Degradation of Bacterial Lipopolysaccharides by Peptide-Coated TiO₂ Nanoparticles

In this study, we report the degradation of smooth and rough lipopolysaccharides (LPS) from Gram-negative bacteria and of lipoteichoic acid (LTA) from Gram-positive bacteria by peptide-coated TiO₂ nanoparticles (TiO₂ NPs). While bare TiO₂ NPs displayed minor binding to both LPS and LTA, coating TiO₂ NPs with the antimicrobial peptide LL-37 dramatically increased the level of binding to both LPS and LTA, decorating these uniformly. Importantly, peptide coating did not suppress reactive oxygen species generation of TiO₂ NPs; hence, UV illumination triggered pronounced degradation of LPS and LTA by peptide-coated TiO₂ NPs. Structural consequences of oxidative degradation were examined by neutron reflectometry for smooth LPS, showing that degradation occurred preferentially in its outer O-antigen tails. Furthermore, cryo-TEM and light scattering showed lipopolysaccharide fragments resulting from degradation to be captured by the NP/lipopolysaccharide coaggregates. The capacity of LL-37-TiO₂ NPs to capture and degrade LPS and LTA was demonstrated to be of importance for their ability to suppress lipopolysaccharide-induced activation in human monocytes at simultaneously low toxicity. Together, these results suggest that peptide-coated photocatalytic NPs offer opportunities for the confinement of infection and inflammation.