Yan-Wen Wang

In vitro toxicity evaluation of graphene oxide on A549 cells

Graphene and its derivatives have attracted great research interest for their potential applications in electronics, energy, materials and biomedical areas. However, little information of their toxicity and biocompatibility is available. Herein, we performed a comprehensive study on the toxicity of graphene oxide (GO) by examining the influences of GO on the morphology, viability, mortality and membrane integrity of A549 cells. The results suggest that GO does not enter A549 cell and has no obvious cytotoxicity. But GO can cause a dose-dependent oxidative stress in cell and induce a slight loss of cell viability at high concentration. These effects are dose and size related, and should be considered in the development of bio-applications of GO. Overall, GO is a pretty safe material at cellular level, which is confirmed by the favorable cell growth on GO film.

Folding/aggregation of graphene oxide and its application in Cu2+ removal.

Graphene oxide (GO) can be aggregated by Cu(2+) in aqueous solution with a huge Cu(2+) absorption capacity. The Cu(2+) causes GO sheets to be folded and also to form large aggregates that were characterized by confocal microscopy and atomic force microscopy. The folding/aggregation is most likely triggered by the coordination between GO and Cu(2+). The equilibrium Cu(2+) concentrations and equilibrium absorption capacity of GO were measured to estimate the maximum absorption capacity of GO for Cu(2+) and the absorption model. GO has a huge absorption capacity for Cu(2+), which is around 10 times of that of active carbon. Representative results are presented and the implication to Cu(2+) removal is discussed.

Superior antibacterial activity of zinc oxide/graphene oxide composites originating from high zinc concentration localized around bacteria.

New materials with good antibacterial activity and less toxicity to other species attract numerous research interest. Taking advantage of zinc oxide (ZnO) and graphene oxide (GO), the ZnO/GO composites were prepared by a facile one-pot reaction to achieve superior antibacterial properties without damaging other species. In the composites, ZnO nanoparticles (NPs), with a size of about 4 nm, homogeneously anchored onto GO sheets. The typical bacterium Escherichia coli and HeLa cell were used to evaluate the antibacterial activity and cytotoxicity of the ZnO/GO composites, respectively. The synergistic effects of GO and ZnO NPs led to the superior antibacterial activity of the composites. GO helped the dispersion of ZnO NPs, slowed the dissolution of ZnO, acted as the storage site for the dissolved zinc ions, and enabled the intimate contact of E. coli with ZnO NPs and zinc ions as well. The close contact enhanced the local zinc concentration pitting on the bacterial membrane and the permeability of the bacterial membrane and thus induced bacterial death. In addition, the ZnO/GO composites were found to be much less toxic to HeLa cells, compared to the equivalent concentration of ZnO NPs in the composites. The results indicate that the ZnO/GO composites are promising disinfection materials to be used in surface coatings on various substrates to effectively inhibit bacterial growth, propagation, and survival in medical devices.

Removal of carbon nanotubes from aqueous environment with filter paper

The potential health and environmental hazards of carbon nanotubes (CNTs) have been a concerned issue. However, in contrast to the wide recognition of the toxicity of CNTs, little attention has been paid to the decontamination/remediation of CNT pollution. In this study, we report that CNTs can be removed from aqueous environment. In the presence of Ca²(+), CNTs aggregate quickly to micron size and then enable easy and effective removal via normal filtration. After filtration, CNT suspension becomes colorless with the remnant CNT concentration less than 0.5 μg mL⁻¹, a safe dose based on the published data. The filtration approach also works well in the presence of typical surfactant and dissolved organic matter. The removal efficiency is Ca²(+) concentration-dependent and regulated by the initial pH value and ionic strength. Our study is helpful for future decontamination of CNTs from aqueous environment.

Enhanced bactericidal toxicity of silver nanoparticles by the antibiotic gentamicin

The alteration of properties of nanomaterials in the environment may change the interaction of the nano–bio interface and the corresponding bio-responses. In this study, we find that the antibiotic gentamicin significantly enhances the antibacterial activities of poly(N-vinyl-2-pyrrolidone) coated silver nanoparticles (Ag-PVP NPs) by altering the properties of silver nanoparticles in culture media. The enhanced antibacterial activities of Ag-PVP NPs against three bacterial strains (S. aureus, E. coli and gentamicin-resistant E. coli) are concluded according to the data of the fractional inhibitory concentration indices, bacterial survival rates and growth curves. A thorough investigation indicates that gentamicin promotes the dissolution of Ag-PVP NPs dramatically, which not only increases the concentration of silver ions in the system but also facilitates the attachment of Ag-PVP NPs onto the surface of bacteria by mitigating the negative charge of the NPs. The corresponding sequence is the augmented bacterial growth inhibition and death. Meanwhile, it is surprisingly found that gentamicin also binds with the dissolved silver ions and then inhibits the antibacterial activity of silver ions. In other words, gentamicin plays a dual role in the antibacterial activity of Ag-PVP NPs. This study is valuable for understanding the bioeffects of nanoparticles in a complex system.