Low Graphene Oxide Concentration Research Articles

Chronic Exposure to Low Concentration of Graphene Oxide Increases Bacterial Pathogenicity via the Envelope Stress Response.

Graphene oxide (GO), which has diverse antimicrobial mechanisms, is a promising material to address antibiotic resistance. Considering the emergence of antibiotic tolerance/resistance due to prolonged exposure to sublethal antibiotics, it is imperative to assess the microbiological effects and related adaptive mechanisms under chronic exposure to sublethal levels of GO, which have rarely been explored. After repetitive exposure to 5 mg/L GO for 200 subcultures (400 days), evolved Escherichia coli (E. coli) cells (EGO) differed significantly from their ancestor cells according to transcriptomic and metabolomic analyses. Contact with GO surfaces transformed E. coli by activating the Cpx envelope stress response (ESR), resulting in more than twofold greater extracellular protease release and biofilm formation. The ESR also modulated the envelope structure and function via increases in membrane fluidity, permeation, and lipopolysaccharide content to fulfill growth requirements and combat envelope stress. As a consequence of metabolic adjustment, EGO cells showed advantages of surviving in an acidic and oxidative environment, which resembles the cytosol of host cells. With these adaptive features, EGO cells exhibited higher pathogenicity than ancestor E. coli cells as evidenced by increased bacterial invasion and intracellular survival and a more severe inflammatory response in macrophage cells. To conclude, we seek to raise awareness of the possible occurrence of microbial adaptation to antimicrobial nanomaterials, which may be implicated in cross-adaptation to harsh environments and eventually the prevalence of virulence.

Application of injectable silk fibroin/graphene oxide hydrogel combined with bone marrow mesenchymal stem cells in bone tissue engineering

The stem cell composite hydrogel scaffold was constructed following its application in bone tissue engineering. For this study, different silk fibroin (SF) hydrogels were prepared by enzyme-catalyzed crosslinking of SF and graphene oxide (GO), and their physicochemical properties and biocompatibility were examined. It has been observed that with the incorporation of GO, the pore size of the scaffold became more regular, and the porosity changed negligibly and also exhibited a stable silk II structure with excellent mechanical properties. Moreover, bone marrow stromal cells (BMSCs) were encapsulated in the hydrogel compared to SF hydrogels either in the absence or in the presence of high concentrations of GO. It has been noted that the cells in the compound gel at a low concentration of GO had shown a better growth capability, proliferation and osteogenic differentiation. Therefore, such injectable BMSCs hydrogel is an excellent biomedical material, possessing potential applications in the field of bone tissue engineering.

Engineering of SnO2-Graphene Oxide Nanoheterojunctions for Selective Room-Temperature Chemical Sensing and Optoelectronic Devices.

The development of high-performing sensing materials, able to detect ppb-trace concentrations of volatile organic compounds (VOCs) at low temperatures, is required for the development of next-generation miniaturized wireless sensors. Here, we present the engineering of selective room-temperature (RT) chemical sensors, comprising highly porous tin dioxide (SnO2)–graphene oxide (GO) nanoheterojunction layouts. The optoelectronic and chemical properties of these highly porous (>90%) p–n heterojunctions were systematically investigated in terms of composition and morphologies. Optimized SnO2–GO layouts demonstrate significant potential as both visible–blind photodetectors and selective RT chemical sensors. Notably, a low GO content results in an excellent UV light responsivity (400 A W–1), with short rise and decay times, and RT high chemical sensitivity with selective detection of VOCs such as ethanol down to 100 ppb. In contrast, a high concentration of GO drastically decreases the RT response to ethanol and results in good selectivity to ethylbenzene. The feasibility of tuning the chemical selectivity of sensor response by engineering the relative amount of GO and SnO2 is a promising feature that may guide the future development of miniaturized solid-state gas sensors. Furthermore, the excellent optoelectronic properties of these SnO2–GO nanoheterojunctions may find applications in various other areas such as optoelectronic devices and (photo)electrocatalysis.

Engineering foam skeletons with multilayered graphene oxide coatings for enhanced energy dissipation

This work shows how to improve the energy dissipation of open-cell polyurethane (PU) foams by creating multilayered graphene oxide (GO) nano-architectures onto the struts via a modified dip-coating process. Pristine PU foams are alternately dip-coated with GO coatings and water-based polyurethane dispersions (PUD) for a given number of times. The GO coating morphologies are carefully adjusted and the inner energy dissipation mechanisms reach the optimized interfacial frictions of GO-PU and GO-GO. Along with the synergistic effect of the multiple interpenetrating structure of GO/PU coating phases, these engineered composite foams with extremely low GO content (~0.12 wt%) afford a significant increase of quasi-static energy dissipation (52%) and dynamic damping (76%) when compared with counterpart foams coated with the same number of pure PUD layers. The specific Young’s modulus and strength of the designed foams also show remarkable enhancements of 310% and 490% respectively compared with those of pristine PU foams.

Microstructural evolution and mechanical investigation of hot stretched graphene oxide reinforced polyacrylonitrile nanofiber yarns

To reveal the enhancement effect of graphene oxide (GO) in polymer nanofiber yarns, polyacrylonitrile (PAN)/GO nanofibers with different GO content (0.1‐0.5 wt%) were electrospun. The alignment of PAN chains and GO in nanofibers was enhanced by hot stretching of the yarn in dry conditions. The microstructure of the composite nanofiber yarns was investigated through X‐ray diffraction, polarized Fourier transform infrared spectroscopy and transmission electron microscopy. The results demonstrated that the hot stretching above Tg of PAN precursor lead to the increased orientation‐induced crystallization and alignment of PAN chain and GO. The yarn with 0.1 wt% GO and stretched by 4 times its length obtained the highest strength and modules (310.88 ± 24.68 MPa and 7.24 ± 0.55 GPa), which were 600% and 500% higher than those of the as‐electrospun pure PAN yarn. The most promising tensile properties found in hot stretched yarns with low GO content was because the strong interaction occurred between PAN molecules and oxygen‐containing functional groups. Indirect evidence of GO aggregation was also presented, which adversely affected the mechanical properties at higher GO content. Composite nanofiber yarns were sewable and weavable, and could be used as a new generation of composite reinforcement after pyrolysis.

3D printing geopolymer nanocomposites: Graphene oxide size effects on a reactive matrix

In previous study, we reported that the addition of graphene oxide (GO) into geopolymer can significantly modified its rheology properties and make it 3D printable. However, the high concentration of GO employment limits the enhancement of mechanical properties. Improving GO reinforcement efficiency with lower GO concentration without sacrificing 3D printability is still a challenge. More importantly, although it has been proved that large graphene oxide (LGO) can reinforce various matrix materials including polymers and ceramics better than that of small graphene oxide (SGO), it is still unclear whether such conclusion can be directly applied to reactive matrix system. We investigate the effects of GO size on mechanical properties of geopolymer with low GO concentration, both at material level and printed structure level. Surprisingly, it is found that the SGO can enhance the mechanical performance of geopolymer more effectively than LGO at material level, which is resulted from the fact that the chemical reaction between geopolymer particles could be severally blocked by LGO. In addition, we also found that the efficiency for the reinforcement at structure level is higher for LGO. Therefore, the size of nano reinforcement should be optimized both for the reinforcement at material and structure level.

Graphene Oxide-Assisted Morphology and Structure of Electrodeposited ZnO Nanostructures.

In this paper, ZnO electrodeposition was studied with the presence of graphene oxide (GO) exploited as a possible structure-directing agent. The effect of deposition potential and duration on the morphology and structure of ZnO was analyzed. The morphology and structure of the hybrids was analyzed by Raman spectroscopy, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). The Raman results indicate a successful modification of ZnO with GO sheets and a hybridization threshold of 10 mg L−1 by the evolution of the defect related band of ZnO at 580 cm−1. The morphology results show that a low GO content only slightly influences the morphology and orientation of ZnO nanostructures while a high content as 10 mg L−1 changes the morphology in nanoplates and growth orientation to lateral. The results show that while GO participated in the deposition reaction, it has a two-fold role, also by structure-controlling ZnO, indicating that the approach is valid for the use of GO as a structure-directing agent for the fabrication of ZnO nanostructures by electrodeposition with varying morphologies and orientations.

Preparation and Characterization of Grafted Natural Rubber/Graphene Oxide Nanocomposites

Vinyltriethoxysilane (VTES) was grafted onto natural rubber (NR) in latex form, using potassium persulfate (KPS) as initiator. The VTES grafted NR (NR-g-VTES) was then further reinforced with graphene oxide (GO) by a mechanical mixing method with different GO loadings to get the rubber composite (GO/NR-g-VTES). The NR-g-VTES was characterized and confirmed by attenuated total teflectance-Fourier transforms infrared spectroscopy (ATR-FTIR). The effect of GO content on the curing characteristics and resulting mechanical properties of the GO/NR-g-VTES were studied and compared with neat NR filled with GO (NR/GO). The maximum and minimum torque and the tensile and tear strength of the NR-g-VTES/GO composites were higher than that of NR/GO. The samples containing low GO concentration showed maximum torque and tensile and tear strength. Dynamic mechanical analysis showed that the interaction between GO and NR-g-VTES was better than that of the GO-reinforced NR.

Ultra-low graphene oxide loading for water permeability, antifouling and antibacterial improvement of polyethersulfone/sulfonated polysulfone ultrafiltration membranes

The aqueous dispersion of graphene oxide (GO) was employed as additive to fabricate antifouling and antibacterial polyethersulfone (PES)/sulfonated polysulfone (SPSf)/GO mixed matrix membranes (MMMs) by the non-solvent induced phase separation (NIPS). The effect of different amounts of GO on the morphology and performance of MMMs were studied. The results showed that the casting solution exhibited an increasing trend in viscosity with increment in GO concentration (from 0 to 0.016 wt%) owing to the hydrogen bonding (H-bonding) interaction among GO, H2O and SPSf. Raman and molecular dynamic (MD) simulations analyses confirmed that there existed H-bonding interaction among SPSf, GO and H2O. Specifically, the agglomeration of GO was inhibited and stable homogeneous casting solution was obtained. Meanwhile, the H-bonding interaction also played a key role in the MMMs structure and improved properties. It was found that GO nanosheets were uniformly embedded to form many cellular-like voids in the asymmetric PES/SPSf/GO MMMs with a sponge-like structure. The pure water flux of the MMMs with a very low GO content of 0.012 wt% was up to 816.9 L/m2h and the rejection of bovine serum albumin (BSA) was more than 99.2% under a pressure of 0.1 MPa. Additionally, the mechanical properties of MMMs was also improved with the increase of GO content. Importantly, the MMMs displayed excellent antifouling and antibacterial performance. A high fouling recovery (94.2%) and antibacterial rate (90.0%) against Escherichia coli (E. coli) obtained were attributed to improved hydrophilicity, enhanced negative charge and GO nano-size effect. In summary, our study provides a simple approach to tailor MMMs with the enhancement of permeation, antifouling and antibacterial properties at a very low content of GO.

New insight into the aggregation of graphene oxide in synthetic surface water: Carbonate nanoparticle formation on graphene oxide

Graphene oxide (GO), used in a wide variety of applications, is increasingly being introduced into aquatic environments; this situation calls for research on GO aggregation and sedimentation to regulate the environmental behaviors and risks. Many studies have investigated the aggregation and the mechanism of GO in water with a single background salt (monosalt system); however, this may not reflect real water environments where multiple salts coexist (multisalt system). A typical synthetic surface water (soft water) with representative multisalts was therefore used to study the aggregation and sedimentation of GO. The GO concentration-dependent aggregation (low concentration aggregation, high concentration stability) was observed in the soft water, and this concentration-dependent aggregation is opposite to the aggregation in monosalt systems (NaCl or CaCl2 solutions). The presence of GO sheets induced the formation of amorphous CaMg(CO3)2 nanoparticles on the GO surfaces in the soft water, and the formed nanoparticles promoted the aggregation and sedimentation of low concentrations of GO through bridging action. Neutral and alkaline conditions were favorable for the formation of CaMg(CO3)2 nanoparticles and the induced GO aggregation. These findings show a new mechanism of GO aggregation in environmentally relevant waters and help us to better evaluate the environmental fate of GO.

Thermal Reduction of Graphene Oxide Mitigates Its In Vivo Genotoxicity Toward Xenopus laevis Tadpoles.

The worldwide increase of graphene family materials raises the question of the potential consequences resulting from their release in the environment and future consequences on ecosystem health, especially in the aquatic environment in which they are likely to accumulate. Thus, there is a need to evaluate the biological and ecological risk but also to find innovative solutions leading to the production of safer materials. This work focuses on the evaluation of functional group-safety relationships regarding to graphene oxide (GO) in vivo genotoxic potential toward X. laevis tadpoles. For this purpose, thermal treatments in H2 atmosphere were applied to produce reduced graphene oxide (rGOs) with different surface group compositions. Analysis performed indicated that GO induced disturbances in erythrocyte cell cycle leading to accumulation of cells in G0/G1 phase. Significant genotoxicity due to oxidative stress was observed in larvae exposed to low GO concentration (0.1 mg·L−1). Reduction of GO at 200 °C and 1000 °C produced a material that was no longer genotoxic at low concentrations. X-ray photoelectron spectroscopy (XPS) analysis indicated that epoxide groups may constitute a good candidate to explain the genotoxic potential of the most oxidized form of the material. Thermal reduction of GO may constitute an appropriate “safer-by-design” strategy for the development of a safer material for environment.

Mechanically robust high flux graphene oxide - nanocellulose membranes for dye removal from water.

Ultrathin graphene oxide (GO) layer was fabricated on cellulose nanofiber (CNF) membrane to achieve robust crosslinker free layered membrane with synergistic water flux and separation performance. Unlike pristine cellulosic or GO membranes, GO-CNF hybrid membranes exhibited significantly improved mechanical stability in both dry and wet states. All membranes showed negative surface zeta potential. GO: CNF membrane (1:100) exhibited significantly high water flux (18,123 ± 574 Lm-2 h-1 bar-1); higher than that of CNF membrane or the hydrophilic commercial reference membrane with comparable pore structure (Nylon 66, 0.2 μm). We hypothyse that a unique surface structure of "standing inserted GO nanosheets" observed at low concentrations of GO contributes enormously to its ultrafast water permeability through creation of numerous water transport nanochannels. The aniosptropic layered membranes exhibited >90% rejection of positively and negatively charged dyes through a combination of electrostatic interaction, hydrophobic interactions and molecular size exclusion. Construction of an ultrathin GO layer on CNF offers a unique and efficient way to prepare highly functional, economical and scalable water purification membranes having significant advantage with respect to flux, mechanical stability and rejection of dyes compared to isotropic membrane with GO nanosheets randomly dispersed in the cellulose nanofibrous network.

Dose-dependent genotoxicity of ammonia-modified graphene oxide particles in lung cancer cells

Graphene oxide (GO), the water soluble form of 2D graphene, has received much attention because of its attractive properties for a wide range of applications and products. Surface modification with different functional groups can improve GO biocompatibility for further biomedical applications. In the present study we have evaluated genotoxicity of pristine and ammonia-modified graphene oxide (GO-NH2) nanoparticles (NPs) in a human lung epithelial cell line, A549, exposed for 24 h to different concentrations of NPs (0.1, 1, 10, 20 and 50 μg/ml). Quantification of reactive oxygen species (ROS) indicated that exposure to higher concentrations of both types of NPs resulted in enhanced ROS generation. The observed comet tail migration in the method of Single Cell Gel Electrophoresis in the cells treated with 20 and 50 μg/ml GO and GO-NH2 indicated presence of damages in DNA. Cell cycle analysis showed that after treatment of A549 cells with increasing concentrations of NPs for 24h the percentage of cells in G0/G1 phase of the cell cycle decreased while the percentage of cells in G2/M increased. The presented results suggest that ammonia-modified GO NPs applied at concentrations higher than 20 μg/ml induced stronger toxicity effect in A549 cells compared to pristine GO and that the use of low concentrations of GO and GO-NH2 NPs is important to avoide adverse biological effects.

Fabrication of graphene oxide blended polyethersulfone membranes via phase inversion assisted by electric field for improved separation and antifouling performance

Novel antifouling blend polyethersulfoune (PES) membranes were prepared via phase inversion assisted by a direct current (DC) electric field with the addition of extremely low concentration of graphene oxide (GO). The GO particles were observed migrating toward the anode and better distributed in the casting solution with a DC electric field exerted. The effect of the applied DC electric field intensity on the properties of blend membranes was systematically investigated. The enrichment of GO on the membrane surface assisted by the electric field was confirmed by the enhanced hydrophilicity and negative charge density, and the XPS results. The blend PES membrane prepared under an electric field of 5000 V cm−1 exhibits not only a high water flux (289.63 Lm−2h−1), which is more than double of the pristine PES membrane (137.67 Lm−2h−1), but also an improved methyl red rejection. The membrane fouling performance was studied with bovine serum albumin (BSA) as model protein. The PES/GO membranes prepared under a 5000 V cm−1 electric field showed an obviously increased flux recovery ratio (FRR) and a decreased irreversible fouling ratio (Rir) value, compared to ones without using an electric field. The membrane fabrication assisted by an electric field opens a new way to enhance hydrophilicity, charge density, separation performance and antifouling ability of mixed matrix membranes.

An auxiliary matrix for routine analysis of small molecules and biological macromolecules using matrix-assisted laser desorption ionization mass spectrometry.

The great hurdles related with matrix-assisted laser desorption/ionization (MALDI) analysis are inhomogeneous crystallization, poor reproducibility, and low sensitivity. To effectively improve the performance of MALDI mass spectrometry (MS), graphene oxide (GO) was first utilized as an auxiliary matrix of the conventional matrices, including 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydoxycyanocinnamic acid (CHCA), 2,4,6-trihydroxyacetophenone (THAP), and 3,5-dimethoxy-4-hydroxycinnamic acid (SA), for the analysis of small molecules and biological macromolecules on different MALDI MS systems. The results revealed that the DHB-GO composite matrix could provide much superior crystal homogenization, better reproducibility, higher sensitivity, and more excellent linearity for the statins' tissue imaging on iMScope than the single-use DHB matrix. Moreover, the DHB-GO dramatically improved the spot-to-spot and shot-to-shot reproducibility, crystal homogenization, sensitivity, and linearity of MALDI-TOF MS for statins' analysis in dried droplet. The capability of THAP on the analysis of lipids, similarly, could be greatly enhanced by the combined use of GO. THAP-GO composite matrix was expected to be widely used in the MALDI MS-based liposome studies. It was also found that CHCA-GO could provide superior analytical performance for peptides. The sensitivity and reproducibility of intact proteins could be greatly improved by SA-GO composite matrix. More importantly, the better reproducibility produced by the composite matrices sufficiently indicated that low concentration (0.1mgmL-1) of GO almost did not cause contamination to MALDI MS system. Thus, GO was proved to be a versatile auxiliary matrix for the MALDI MS-based routine analysis of small molecules and biological macromolecules. Graphical abstract ᅟ.

Self-assembling GO/modified HEC hybrid stabilized pickering emulsions and template polymerization for biomedical hydrogels

Graphene oxide(GO), as an amphiphilic and biocompatible material, is often used to prepare Pickering emulsion. However, the preparation of stable Pickering emulsion by a low concentration of GO is very challenging. In this research, we prepared the hydrophobic modified hydroxyethyl cellulose (mHEC) which contained quaternary ammonium group and GO which the water contact angle was 84°–86°. A stable, low cost, and biocompatible Pickering emulsion was fabricated by a low concentration of GO and different contents of mHEC. The effects of mHEC concentration, electrolyte concentration, pH, and oil/water ratio on the stability of Pickering emulsion were investigated. What’s more, we prepared the biomedical macroporous polyacrylamide hydrogel by the GO/mHEC composite stabilized emulsion template for drug controlled-release. The composite hydrogel by Pickering emulsion template is a potential drug controlled-release delivery platforms. Furthermore, our strategy is extremely versatile, as Pickering particles, polymer and the monomer of hydrogel can all be varied.

Graphene Oxide Affects Growth and Resistance to Sclerotinia sclerotiorum in Brassica napus L.

Researchers have shown that graphene oxide has a significant effect on plant and pathogen growth and development. To better understand the effect of graphene oxide on the resistance of Brassica napus L. to Sclerotinia sclerotiorum, Zhongshuang 11 was used to evaluate changes in the morphology and physiology after graphene oxide treatment. Detached leaf inoculation was used to detect S. sclerotiorum infection in rapeseed. The results indicated that treatment with a low concentration of graphene oxide had no significant effect on the growth of B. napus "Zhongshuang 11." Graphene oxide inhibited S. sclerotiorum in PDA medium. Treatment with 15 mg/L graphene oxide for 8-24 h in seeds and 8-16 h in seedlings suppressed S. sclerotiorum growth compared to the control samples. These results demonstrate that a low concentration of graphene oxide did not harm the growth of B. napus but did enhance its resistance to S. sclerotiorum.

Response of antibiotic resistance genes abundance by graphene oxide during the anaerobic digestion of swine manure with copper pollution

The pollution of various environments with antibiotic resistance genes (ARGs) is an urgent problem that needs to be addressed, especially in heavy metal-polluted environments. This study investigated the responses of ARGs and mobile genetic elements (MGEs) to the addition of graphene oxide (GO) to swine manure containing a high concentration copper during anaerobic digestion. The total copy numbers of ARGs and MGEs were significantly enhanced by the pressure due to Cu. GO significantly decreased the ARG and MGE copy numbers, where the low GO concentration performed better than the high GO concentration. Network analysis showed that most of the ARGs and MGEs co-occurred and they shared the same major potential host bacteria. The contributions of different factors to ARG abundances were assessed by redundancy analysis and MGEs had the most important effect on the fate of ARGs. Thus, GO may reduce the abundance of ARGs mainly by removing MGEs.

Effect of Graphene Oxide on Algal Toxicity of Dibutyl Phthalate

Marine microalgae, Platymonas helgolondica var. tsingtaoensis, were used as experimental subjects to study the acute toxic effects of graphene oxide (GO) and dibutyl phthalate (DBP), both individually and together. The growth of algae cells, production of photosynthetic pigments, cell permeability, and oxidative stress were investigated. The effects of GO on the algal toxicity of DBP were evaluated. The results showed that low concentrations of GO (0.1-10 mg·L-1) had no significant effect on algae density and chlorophyll production of Platymonas helgolondica var. tsingtaoensis (P<0.05). However, the algae cell permeability increased significantly with GO concentration (P<0.05) and reached 2.2 times that of the control group at 10 mg·L-1. The EC50, 96 h value of DBP for Platymonas helgolondica var. tsingtaoensis was (11.14±0. 80) mg·L-1, which, in terms of toxicity, was much higher than that of GO (EC50, 96 h>100 mg·L-1). At a GO concentration of 1 mg·L-1, the EC50, 96 h value of DBP decreased to (4.93±2.14) mg·L-1, showing that low concentrations of GO enhanced the algae toxicity of DBP. When 1 mg·L-1 of GO was added, low concentrations of DBP (0.1-2 mg·L-1) did not have any significant effect on algae density, chlorophyll production, cell permeability, ROS, and SOD. However, the inhibitory effects of high concentrations of DPB (4 mg·L-1) on algae density and chlorophyll production were enhanced by GO, thereby increasing the average ROS and SOD in algae cells by 21% and 7%, respectively. SEM images showed that GO was the primary factor responsible for increasing the coverage and packing of, and the aggregation effect on, algae cells, which could be the reasons for the increased toxicity of DBP. The results of our study can provide data to reveal the risk of novel carbon nanomaterial pollutants to marine organisms.

Extraordinary improvement of ablation resistance of carbon/phenolic composites reinforced with low loading of graphene oxide

The effectiveness of graphene oxide (GO) on improving the ablation resistance of composite is investigated by incorporating a low concentration of GO (0.1 wt%) into the carbon/phenolic (CF/PR). The X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy analyses reveal that the superiority of GO-filled composite over the neat in terms of thermal resistance is associated with the promoted char yield of PR and graphitization of fibers by the addition of GO. Molecular dynamics simulations identify the GO inside the matrix, even a small concentration, as a nuclei agent for the graphitized crystal growth of carbonized PR. And the GO at the fiber-matrix interface can bond to the fibers at extreme ablation temperatures, which promotes the formation of the Stone-Thrower-Wales defect (xy plane) and sp2 hybridization (z direction) at the graphene-fiber interface, and further increases the graphitization degree of fibers.