Boosting Membrane Interactions and Antimicrobial Effects of Photocatalytic Titanium Dioxide Nanoparticles by Peptide Coating

Abstract

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.

Photochemical Strategies toward Precision Targeting against Multidrug-Resistant Bacterial Infections

“…As initially predicted, Van-Ag@TiO 2 showed the capacity to target bacterial membranes and possessed a higher selective phototoxicity on Van-sensitive Desulfotomaculum as compared to Van-resistant bacteria. The finding proved the selective 158 It is shown that the LL-37 coating could increase membrane rupture by TiO 2 NPs for G + and G − bacteria instead of human monocytes. And the AMP coating was capable of selectively enhancing the antimicrobial effects of photocatalytic TiO 2 NPs.…”

“…Analogously, Caselli et al laid an AMP LL-37 coating onto photocatalytic TiO 2 NPs . It is shown that the LL-37 coating could increase membrane rupture by TiO 2 NPs for G + and G – bacteria instead of human monocytes.…”

Conformational control of antimicrobial peptide amphiphilicity: consequences for boosting membrane interactions and antimicrobial effects of photocatalytic TiO2 nanoparticles

“…As a result of the build-up of the positive ζ -potential, the TiO 2 NPs are colloidally stabilized on the peptide coating, seen from a much smaller average particle size of 147 ± 16 nm at peptide concentrations of 50 mM and above. Keeping in mind that the primary particle size for the fully dispersed TiO 2 NPs is 2–8 nm, 7 each composite NP contains multiple TiO 2 NPs which have an outer region dominated by the peptide. While a minor increase in positive ζ -potential and a minor decrease in effective particle diameter is observed as a function of EFK17d and EFK17-d concentrations, the binding of these peptides to the TiO 2 NPs is too weak to allow colloidal stabilization of the aggregating TiO 2 NPs.…”

“…20 μL of bare TiO 2 NPs were subsequently added from a concentrated stock dispersion (5000 ppm TiO 2 in 10 mM acetate buffer, pH 5.4) under continuous stirring to obtain a 100 ppm TiO 2 NP dispersion (for live/dead bacterial viability assay, 40 μL of bare TiO 2 NPs were used instead to obtain a final TiO 2 concentration of 200 ppm in the mixed peptide/NP dispersion, to be diluted down to 100 ppm upon mixing with bacteria). Following this, pH of the dispersion was adjusted to 9.4, where TiO 2 NPs display a negative surface charge, 7 to promote binding with positively charged peptides. The dispersions were subsequently tip-sonicated (UP50H, Hielscher Ultrasonics GmbH, Germany (50 W, 30 kHz) in an intermittent-pulse mode (5 s), at 100% amplitude) for 15 minutes in an ice bath.…”

“…3 Addressing this, we previously demonstrated that photocatalytic TiO 2 NPs coated with antimicrobial peptides (AMPs 4–6 ) may be used to enhance NP binding to bacterial membranes, thereby increasing the probability of ROS generated during illumination reaching the bacterial membrane during their short lifetime. 7…”