Coating UV‑activated titanium‑dioxide nanoparticles with the natural antimicrobial peptide LL‑37 keeps their ability to make reactive oxygen species, but makes them stick better to bacterial membranes and kill bacteria more efficiently while leaving human‑like cells mostly unharmed. The peptide stays intact enough during a short UV burst to guide the particles to the right targets.

Photocatalytic nanoparticles offer antimicrobial effects under illumination due to the formation of reactive oxygen species (ROS), capable of degrading bacterial membranes. ROS may, however, also degrade human cell membranes and trigger toxicity. Since antimicrobial peptides (AMPs) may display excellent selectivity between human cells and bacteria, these may offer opportunities to effectively "target" nanoparticles to bacterial membranes for increased selectivity. Investigating this, photocatalytic TiO₂ nanoparticles (NPs) are coated with the AMP LL-37, and ROS generation is found by C₁₁-BODIPY to be essentially unaffected after AMP coating. Furthermore, peptide-coated TiO₂ NPs retain their positive ζ-potential also after 1-2 h of UV illumination, showing peptide degradation to be sufficiently limited to allow peptide-mediated targeting. In line with this, quartz crystal microbalance measurements show peptide coating to promote membrane binding of TiO₂ NPs, particularly so for bacteria-like anionic and cholesterol-void membranes. As a result, membrane degradation during illumination is strongly promoted for such membranes, but not so for mammalian-like membranes. The mechanisms of these effects are elucidated by neutron reflectometry. Analogously, LL-37 coating promoted membrane rupture by TiO₂ NPs for Gram-negative and Gram-positive bacteria, but not for human monocytes. These findings demonstrate that AMP coating may selectively boost the antimicrobial effects of photocatalytic NPs.