Polymer-Coated Titanium Dioxide Nanoparticles with Enhanced Antimicrobial Activity: Mechanistic Insights into Particle-Membrane Interactions

While surface modifications are widely pursued to improve antimicrobial performance of photocatalytic nanoparticles (NPs), the particle-membrane interactions responsible for these effects remain underexplored.We address this gap by investigating the influence of coating TiO₂ NPs with the cationic polymer PDMAEMA (poly((2-dimethylamino)ethyl methacrylate) methyl chloride quaternary salt).In contrast to bare TiO2, the coated NPs adsorbs extensively to negatively charged bacteria and bacteria-like membranes, boosting membrane permeabilization upon UV illumination due to formation of reactive oxygen species (ROS).The PDMAEMA coating was demonstrated not to interfere with ROS formation and to withstand UV illumination over time-scales sufficient for membrane binding and disruption.Such effects were highly localized near membrane-bound NPs, which in turn showed preferential localization at poles and nodes of Escherichia coli bacteria.Hypothesizing this to be driven by co-localization with anionic cardiolipin, studies with giant vesicles containing cardiolipin either uniformly distributed or present in segregated domains showed that the polymer coated TiO2 NPs preferentially bind to cardiolipin-rich regions of the membrane.Together, these results expand on conventional studies of NP interactions with bacteria and bacteria-like membranes and demonstrate that localized interactions must be considered in studies of bacterial membrane interactions of photocatalytic NPs.