Effects of Embedded Carbon Nanotube on Properties of Biomembrane

Antibacterial Activity of Manganese Dioxide Nanosheets by ROS-Mediated Pathways and Destroying Membrane Integrity

Manganese dioxide (MnO₂) nanosheets have shown exciting potential in nanomedicine because of their ultrathin thickness, large surface area, high near-infrared (NIR) absorbance and good biocompatibility. However, the effect of MnO₂ nanosheets on bacteria is still unclear. In this study, MnO₂ nanosheets were shown for the first time to possess highly efficient antibacterial activity by using Salmonella as a model pathogen. The growth curve and surface plate assay uncovered that 125 μg/mL MnO₂ nanosheets could kill 99.2% of Salmonella, which was further verified by fluorescence-based live/dead staining measurement. Mechanism analysis indicated that MnO₂ nanosheet treatment could dramatically induce reactive oxygen species production, increase ATPase activity and cause the leakage of electrolytes and protein contents, leading to bacterial death. These results uncover the previously undefined role of MnO₂ nanosheets and provide novel strategies for developing antimicrobial agents.

Interactions of Functionalized Multi-Wall Carbon Nanotubes with Giant Phospholipid Vesicles as Model Cellular Membrane System

Carbon Nanotubes (CNTs) are considered alternative materials for the design of advanced drug and gene delivery vectors. However, the mechanism responsible for the cellular membrane intake of CNTs is not well understood. In the present study, we show how multi-walled carbon nanotubes (MWCNTs) owning different surface properties, interact with giant unilamellar vesicles (GUVs), a simple model system for cellular membranes. In particular, we want to address the hydrophilic/hydrophobic interactions between MWCNTs and lipid membranes and the subsequent mechanical properties changes of the systems. In order to elucidate this interaction, we made the following chemical modifications on MWCNTs: oxidized MWCNTs (ox-MWCNTs) displaying reduced hydrophobic surface character, pristine MWCNTs (p-MWCNTs), and alkyl functionalized MWCNTs (alk-MWCNTs) exhibiting enhanced hydrophobic surface properties, were put in contact with GUVs and observed by confocal microscopy. Our observations revealed that the interaction between the CNTs and GUVs depends on the type of chemical functionalization: ox-MWCNTs remain at the membrane interacting with the polar head of the phospholipids, p-MWCNTs internalize GUVs spontaneously, and alk-MWCNTs persist inside the membrane. The mechanical properties of MWCNTs@GUVs systems were measured using the electrodeformation method, which shows an increased bending stiffness (κ) of the GUVs as MWCNTs concentration increases. High concentrations of p-MWCNTs and alk-MWCNTs induced vesicle adhesion; p-MWCNTs produced a considerable reduction in the average size of the GUVs, while alk-MWCNTs form complex stable structures inside the membrane. The statistical analyses of the experimental results are compared with available computer simulations. The picture emerging from our results is that the interaction between GUVs and MWCNTs is due mainly to hydrophobicity.

Graphene oxide exhibits broad-spectrum antimicrobial activity against bacterial phytopathogens and fungal conidia by intertwining and membrane perturbation

To understand the interaction mechanism between graphene oxide (GO) and typical phytopathogens, a particular investigation was conducted about the antimicrobial activity of GO against two bacterial pathogens (P. syringae and X. campestris pv. undulosa) and two fungal pathogens (F. graminearum and F. oxysporum). The results showed that GO had a powerful effect on the reproduction of all four pathogens (killed nearly 90% of the bacteria and repressed 80% macroconidia germination along with partial cell swelling and lysis at 500 μg mL(-1)). A mutual mechanism is proposed in this work that GO intertwinds the bacteria and fungal spores with a wide range of aggregated graphene oxide sheets, resulting in the local perturbation of their cell membrane and inducing the decrease of the bacterial membrane potential and the leakage of electrolytes of fungal spores. It is likely that GO interacts with the pathogens by mechanically wrapping and locally damaging the cell membrane and finally causing cell lysis, which may be one of the major toxicity actions of GO against phytopathogens. The antibacterial mode proposed in this study suggests that the GO may possess antibacterial activity against more multi-resistant bacterial and fungal phytopathogens, and provides useful information about the application of GO in resisting crop diseases.

Broad-spectrum antibacterial activity of carbon nanotubes to human gut bacteria

Carbon nanotubes (CNTs) hold promise in manufacturing, environmental, and biomedical applications, as well as food and agricultural industries. Previous observations have shown that CNTs have antimicrobial activity; however, the impact of CNTs to human gut microbes has not been investigated. Here, the antibacterial activity of CNTs against the microbes commonly encountered in the human digestion system--L. acidophilus, B. adolescentis, E. coli, E. faecalis, and S. aureus--are evaluated. The bacteria studied include pathogenic and non-pathogenic, gram-positive and negative, and both sphere and rod strains. In this study, CNTs, including single-walled CNTs (SWCNTs, 1-3 μm), short and long multi-walled CNTs (s-MWCNTs: 0.5-2 μm; l-MWCNTs: >50 μm), and functionalized multi-walled CNTs (hydroxyl- and carboxyl-modification, 0.5-2 μm), all have broad-spectrum antibacterial effects. Notably, CNTs may selectively lyse the walls and membranes of human gut microbes, depending on not only the length and surface functional groups of CNTs, but also the shapes of the bacteria. The mechanism of antibacterial activity is associated with their diameter-dependent piercing and length-dependent wrapping on the lysis of microbial walls and membranes, inducing release of intracellular components DNA and RNA and allowing a loss of bacterial membrane potential, demonstrating complete destruction of bacteria. Thin and rigid SWCNT show more effective wall/membrane piercing on spherical bacteria than MWCNTs. Long MWCNT may wrap around gut bacteria, increasing the area making contact with the bacterial wall. This work suggests that CNTs may be broad-spectrum and efficient antibacterial agents in the gut, and selective application of CNTs could reduce the potential hazard to probiotic bacteria.

Novel Ultrathin Membranes Composed of Organic Ions

Until recently, construction of bilayers was an exclusive mission of nature. It requires careful choice of compounds, whose delicate interplay between head group attraction and chain repulsion engenders a truly unique balance over a narrow temperature range. We report the investigation of artificial bilayers composed of long-chained organic ions, such as dodecyltrimethylammonium (DMA(+)) and perfluorooctaonate (PFO(-)). Various ratios of DMA/PFO surfactants result in bilayers of different stability, thickness, area per molecule, and density profiles. In our quest for water filtration, we incorporated aquaporin protein into the DMA/PFO bilayer but did not observe sufficient stability of the system. We discuss further steps to utilize these surfactant bilayers as highly selective, salt-impermeable membranes.