It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. An international team of physicists involving Jean-Baptiste Fleury from our SFB (B4) demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP–membrane interactions was presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon was demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram‐positive and Gram‐negative bacteria. Hydrophilic and hydrophobic quasi‐spherical and star‐shaped gold (Au)NPs were synthesized to explore the antibacterial mechanism of non‐translocating AuNPs. Direct observation of nanoparticle‐induced membrane tension and squeezing was demonstrated using a custom‐designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi‐spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques were used to characterize the NP–bacterial‐membrane interactions. This combination of experimental and theoretical results confirmed the proposed mechanism of membrane‐tension‐induced (mechanical) killing of bacterial cells by non‐translocating NPs. This work is now published in the renowned journal Advanced Materials".

Press release of Saarland University - click here

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