A model membrane system has been developed, which mimics the outer membrane of Gram negative bacteria. The structure is based on a tethered monolayer which has been fused with vesicles containing lipopolysaccharide molecules. The effect of the composition of the monolayer and the lipids in the outer layer on the structural and electrical properties of the membrane has been investigated. By using electrochemical impedance spectroscopy as well as neutron scattering techniques, it could be shown that a relatively high tethering density and a small amount of diluting lipids in the outer membrane leaflet leads to the formation of a stable solid supported membrane. The influence of divalent ions on the membrane stability has been probed as well as the interaction of the bilayer with the antibiotic colistin. A number of different architectures were developed, suited to both the study of bacterial membrane proteins and the screening of antimicrobial activity of potential drug candidates.
Gold nanoparticles are widely used in biomedical applications. Their ease of surface modification, biocompatibility and the presence of surface plasmons makes them ideal tools for a variety of investigations. Polyelectrolyte-coated gold nanoparticles are employed in areas such as imaging, drug delivery and gene therapy; however, it is not well understood how different factors such as the polyelectrolyte and salt concentration affect the coating on the nanoparticles and hence their performance. Here, these parameters were systematically varied and their effect on the stability of the colloidal nanoparticle suspension was monitored. An increase in the polyelectrolyte concentration from 0 to 30 mg/mL led to a red shift of the surface plasmon peak and an increase in the zeta potential. Concentrations between 5 mg/mL and 30 mg/mL resulted in the most stable systems, with 1 mg/mL being the most unstable. Stable nanoparticle suspensions were formed in salt concentrations below 50 mM, while higher concentrations caused colloidal instability and irreversible aggregation.
Surface modified gold nanoparticles are becoming more and more popular for use in biomaterials due to the possibility for specific targeting and increased biocompatibility. This review provides a summary of the recent literature surrounding polyelectrolyte coatings on spherical gold nanoparticles and their potential biomedical applications. The synthesis and layer-by layer coating approach are briefly discussed together with common characterisation methods. The potential applications and recent developments in drug delivery, gene therapy, photothermal therapy and imaging are summarized as well as the effects on cellular uptake and toxicity. Finally, the future outlook for polyelectrolyte coated gold nanoparticles is explored, focusing on their use in biomedicine.
Antibiotic resistance will be one of the most prominent challenges to health-care systems in the coming decades, with the OECD predicting that up to 2.4 million deaths will be caused between 2015 and 2050 by drug-resistant bacterial infections in first-world countries alone, with infections costing health-care systems billions of dollars each year. Developing new methods to increase bacterial susceptibility toward drugs is an important step in treating resistant infections. Here, the synergistic effects of gold nanoparticles and the antibiotic drug colistin sulfate have been examined. A tethered lipid bilayer membrane was used to mimic a Gram-negative bacterial cell membrane. Exposing the membrane to gold nanoparticles prior to adding the antibiotic significantly increased the effect of the antibiotic on the membrane. Cationic gold nanoparticles could thus be used to enhance bacterial susceptibility to antibiotics, leading to a more potent treatment.
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