Graphene-based antibacterial paper

Graphene is a monolayer of tightly packed carbon atoms that possesses many interesting properties and has numerous exciting applications. In this work, we report the antibacterial activity of two water-dispersible graphene derivatives, graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets. Such graphene-based nanomaterials can effectively inhibit the growth of E. coli bacteria while showing minimal cytotoxicity. We have also demonstrated that macroscopic freestanding GO and rGO paper can be conveniently fabricated from their suspension via simple vacuum filtration. Given the superior antibacterial effect of GO and the fact that GO can be mass-produced and easily processed to make freestanding and flexible paper with low cost, we expect this new carbon nanomaterial may find important environmental and clinical applications.

Cytotoxicity of graphene oxide and graphene in human erythrocytes and skin fibroblasts

Two-dimensional carbon-based nanomaterials, including graphene oxide and graphene, are potential candidates for biomedical applications such as sensors, cell labeling, bacterial inhibition, and drug delivery. Herein, we explore the biocompatibility of graphene-related materials with controlled physical and chemical properties. The size and extent of exfoliation of graphene oxide sheets was varied by sonication intensity and time. Graphene sheets were obtained from graphene oxide by a simple (hydrazine-free) hydrothermal route. The particle size, morphology, exfoliation extent, oxygen content, and surface charge of graphene oxide and graphene were characterized by wide-angle powder X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, dynamic light scattering, and zeta-potential. One method of toxicity assessment was based on measurement of the efflux of hemoglobin from suspended red blood cells. At the smallest size, graphene oxide showed the greatest hemolytic activity, whereas aggregated graphene sheets exhibited the lowest hemolytic activity. Coating graphene oxide with chitosan nearly eliminated hemolytic activity. Together, these results demonstrate that particle size, particulate state, and oxygen content/surface charge of graphene have a strong impact on biological/toxicological responses to red blood cells. In addition, the cytotoxicity of graphene oxide and graphene sheets was investigated by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. However, appropriate alternate assessments, using the water-soluble tetrazolium salt (WST-8), trypan blue exclusion, and reactive oxygen species assay reveal that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e., whether or not aggregation occurs) and mode of interaction with cells (i.e., suspension versus adherent cell types).

Cytotoxicity effects of graphene and single-wall carbon nanotubes in neural phaeochromocytoma-derived PC12 cells

Graphitic nanomaterials such as graphene layers (G) and single-wall carbon nanotubes (SWCNT) are potential candidates in a large number of biomedical applications. However, little is known about the effects of these nanomaterials on biological systems. Here we show that the shape of these materials is directly related to their induced cellular toxicity. Both G and SWCNT induce cytotoxic effects, and these effects are concentration- and shape-dependent. Interestingly, at low concentrations, G induced stronger metabolic activity than SWCNT, a trend that reversed at higher concentrations. Lactate dehydrogenase levels were found to be significantly higher for SWCNT as compared to the G samples. Moreover, reactive oxygen species were generated in a concentration- and time-dependent manner after exposure to G, indicating an oxidative stress mechanism. Furthermore, time-dependent caspase 3 activation after exposure to G (10 microg/mL) shows evidence of apoptosis. Altogether these studies suggest different biological activities of the graphitic nanomaterials, with the shape playing a primary role.

In vivo pharmacokinetics, long-term biodistribution, and toxicology of PEGylated graphene in mice

Graphene has emerged as interesting nanomaterials with promising applications in a range of fields including biomedicine. In this work, for the first time we study the long-term in vivo biodistribution of (125)I-labeled nanographene sheets (NGS) functionalized with polyethylene glycol (PEG) and systematically examine the potential toxicity of graphene over time. Our results show that PEGylated NGS mainly accumulate in the reticuloendothelial system (RES) including liver and spleen after intravenous administration and can be gradually cleared, likely by both renal and fecal excretion. PEGylated NGS do not cause appreciable toxicity at our tested dose (20 mg/kg) to the treated mice in a period of 3 months as evidenced by blood biochemistry, hematological analysis, and histological examinations. Our work greatly encourages further studies of graphene for biomedical applications.

Graphene oxide: a nonspecific enhancer of cellular growth

There have been multiple conflicting reports about the biocompatibility and antimicrobial activity of graphene oxide. To address this, we conducted a study to characterize the antimicrobial properties of graphene oxide (GO) and its biocompatibility with mammalian cells. When GO was added to a bacterial culture at 25 μg/mL, the results showed that bacteria grew faster and to a higher optical density than cultures without GO. Scanning electron microscopy indicated that bacteria formed dense biofilms in the presence of GO. This was shown by a large mass of aggregated cells and extracellular polymeric material. Bacterial growth on filters coated with 25 and 75 μg of GO grew 2 and 3 times better than on filters without GO. Closer analysis showed that bacteria were able to attach and proliferate preferentially in areas containing the highest GO levels. Graphene oxide films failed to produce growth inhibition zones around them, indicating a lack of antibacterial properties. Also, bacteria were able to grow on GO films to 9.5 × 10(9) cells from an initial inoculation of 1.0 × 10(6), indicating that it also lacks bacteriostatic activity. Thus, silver-coated GO films were able to produce clearing zones and cell death. Also, graphene oxide was shown to greatly enhance the attachment and proliferation of mammalian cells. This study conclusively demonstrates that graphene oxide does not have intrinsic antibacterial, bacteriostatic, and cytotoxic properties in both bacteria and mammalian cells. Furthermore, graphene oxide acts as a general enhancer of cellular growth by increasing cell attachment and proliferation.

Toxicity of graphene-family nanoparticles: a general review of the origins and mechanisms

Due to their unique physicochemical properties, graphene-family nanomaterials (GFNs) are widely used in many fields, especially in biomedical applications. Currently, many studies have investigated the biocompatibility and toxicity of GFNs in vivo and in intro. Generally, GFNs may exert different degrees of toxicity in animals or cell models by following with different administration routes and penetrating through physiological barriers, subsequently being distributed in tissues or located in cells, eventually being excreted out of the bodies. This review collects studies on the toxic effects of GFNs in several organs and cell models. We also point out that various factors determine the toxicity of GFNs including the lateral size, surface structure, functionalization, charge, impurities, aggregations, and corona effect ect. In addition, several typical mechanisms underlying GFN toxicity have been revealed, for instance, physical destruction, oxidative stress, DNA damage, inflammatory response, apoptosis, autophagy, and necrosis. In these mechanisms, (toll-like receptors-) TLR-, transforming growth factor β- (TGF-β-) and tumor necrosis factor-alpha (TNF-α) dependent-pathways are involved in the signalling pathway network, and oxidative stress plays a crucial role in these pathways. In this review, we summarize the available information on regulating factors and the mechanisms of GFNs toxicity, and propose some challenges and suggestions for further investigations of GFNs, with the aim of completing the toxicology mechanisms, and providing suggestions to improve the biological safety of GFNs and facilitate their wide application.

Prospects and challenges of graphene in biomedical applications

Graphene materials have entered a phase of maturity in their development that is characterized by their explorative utilization in various types of applications and fields from electronics to biomedicine. Herein, we describe the recent advances made with graphene-related materials in the biomedical field and the challenges facing these exciting new tools both in terms of biological activity and toxicological profiling in vitro and in vivo. Graphene materials today have mainly been explored as components of biosensors and for construction of matrices in tissue engineering. Their antimicrobial activity and their capacity to act as drug delivery platforms have also been reported, however, not as coherently. This report will attempt to offer some perspective as to which areas of biomedical applications can expect graphene-related materials to constitute a tool offering improved functionality and previously unavailable options.

Minimizing oxidation and stable nanoscale dispersion improves the biocompatibility of graphene in the lung

To facilitate the proposed use of graphene and its derivative graphene oxide (GO) in widespread applications, we explored strategies that improve the biocompatibility of graphene nanomaterials in the lung. In particular, solutions of aggregated graphene, Pluronic dispersed graphene, and GO were administered directly into the lungs of mice. The introduction of GO resulted in severe and persistent lung injury. Furthermore, in cells GO increased the rate of mitochondrial respiration and the generation of reactive oxygen species, activating inflammatory and apoptotic pathways. In contrast, this toxicity was significantly reduced in the case of pristine graphene after liquid phase exfoliation and was further minimized when the unoxidized graphene was well-dispersed with the block copolymer Pluronic. Our results demonstrate that the covalent oxidation of graphene is a major contributor to its pulmonary toxicity and suggest that dispersion of pristine graphene in Pluronic provides a pathway for the safe handling and potential biomedical application of two-dimensional carbon nanomaterials.

Graphene in the aquatic environment: adsorption, dispersion, toxicity and transformation

Graphene-family nanomaterials (GFNs) including pristine graphene, reduced graphene oxide (rGO) and graphene oxide (GO) offer great application potential, leading to the possibility of their release into aquatic environments. Upon exposure, graphene/rGO and GO exhibit different adsorption properties toward environmental adsorbates, thus the molecular interactions at the GFN-water interface are discussed. After solute adsorption, the dispersion/aggregation behaviors of GFNs can be altered by solution chemistry, as well as by the presence of colloidal particles and biocolloids. GO has different dispersion performance from pristine graphene and rGO, which is further demonstrated from surface properties. Upon exposure in aquatic environments, GFNs have adverse impacts on aquatic organisms (e.g., bacteria, algae, plants, invertebrates, and fish). The mechanisms of GFNs toxicity at the cellular level are reviewed and the remaining unclear points on toxic mechanisms such as membrane damage are presented. Moreover, we highlight the transformation routes of GO to rGO. The degradation of GFNs upon exposure to UV irradiation and/or biota is also reviewed. In view of the unanswered questions, future research should include comprehensive characterization of GFNs, new approaches for explaining GFNs aggregation, environmental behaviors of metastable GO, and the relationship between dispersion of GFNs and the related adsorption properties.

Behavior and toxicity of graphene and its functionalized derivatives in biological systems

Graphene, as a class of 2D carbon nanomaterial, has attracted tremendous interest in different areas in recent years including biomedicine. The toxicity and behavior of graphene in biological systems are thus important fundamental issues that require significant attention. In this article, the toxicity of graphene is reviewed by describing the behavior of graphene and its derivatives in microorganisms, cells, and animals. Despite certain inconsistencies in several detailed experimental results and hypotheses of toxicity mechanisms, results from numerous reports all agree that the physicochemical properties such as surface functional groups, charges, coatings, sizes, and structural defects of graphene may affect its in vitro/in vivo behavior as well as its toxicity in biological systems. It is hoped that this review article will provide an overview understanding of the impacts, behavior, and toxicology of graphene and its derivatives in various biological systems.

Differential nano-bio interactions and toxicity effects of pristine versus functionalized graphene

We report the effect of carboxyl functionalization of graphene in pacifying its strong hydrophobic interaction with cells and associated toxic effects. Pristine graphene was found to accumulate on the cell membrane causing high oxidative stress leading to apoptosis, whereas carboxyl functionalized hydrophilic graphene was internalized by the cells without causing any toxicity.

Crucial Role of Lateral Size for Graphene Oxide in Activating Macrophages and Stimulating Pro-inflammatory Responses in Cells and Animals

Graphene oxide (GO) is increasingly used in biomedical applications because it possesses not only the unique properties of graphene including large surface area and flexibility but also hydrophilicity and dispersibility in aqueous solutions. However, there are conflicting results on its biocompatibility and biosafety partially due to large variations in physicochemical properties of GO, and the role of these properties including lateral size in the biological or toxicological effects of GO is still unclear. In this study, we focused on the role of lateral size by preparing a panel of GO samples with differential lateral sizes using the same starting material. We found that, in comparison to its smaller counterpart, larger GO showed a stronger adsorption onto the plasma membrane with less phagocytosis, which elicited more robust interaction with toll-like receptors and more potent activation of NF-κB pathways. By contrast, smaller GO sheets were more likely taken up by cells. As a result, larger GO promoted greater M1 polarization, associated with enhanced production of inflammatory cytokines and recruitment of immune cells. The in vitro results correlated well with local and systemic inflammatory responses after GO administration into the abdominal cavity, lung, or bloodstream through the tail vein. Together, our study delineated the size-dependent M1 induction of macrophages and pro-inflammatory responses of GO in vitro and in vivo. Our data also unearthed the detailed mechanism underlying these effects: a size-dependent interaction between GO and the plasma membrane.

Improved In Vitro and In Vivo Biocompatibility of Graphene Oxide through Surface Modification: Poly(Acrylic Acid)-Functionalization is Superior to PEGylation

The unique physicochemical properties of two-dimensional (2D) graphene oxide (GO) could greatly benefit the biomedical field; however, recent research demonstrated that GO could induce in vitro and in vivo toxicity. We determined the mechanism of GO induced toxicity, and our in vitro experiments revealed that pristine GO could impair cell membrane integrity and functions including regulation of membrane- and cytoskeleton-associated genes, membrane permeability, fluidity and ion channels. Furthermore, GO induced platelet depletion, pro-inflammatory response and pathological changes of lung and liver in mice. To improve the biocompatibility of pristine GO, we prepared a series of GO derivatives including aminated GO (GO-NH2), poly(acrylamide)-functionalized GO (GO-PAM), poly(acrylic acid)-functionalized GO (GO-PAA) and poly(ethylene glycol)-functionalized GO (GO-PEG), and compared their toxicity with pristine GO in vitro and in vivo. Among these GO derivatives, GO-PEG and GO-PAA induced less toxicity than pristine GO, and GO-PAA was the most biocompatible one in vitro and in vivo. The differences in biocompatibility were due to the differential compositions of protein corona, especially immunoglobulin G (IgG), formed on their surfaces that determine their cell membrane interaction and cellular uptake, the extent of platelet depletion in blood, thrombus formation under short-term exposure and the pro-inflammatory effects under long-term exposure. Overall, our combined data delineated the key molecular mechanisms underlying the in vivo and in vitro biological behaviors and toxicity of pristine GO, and identified a safer GO derivative that could be used for future applications.

Graphene Nanomaterials: Synthesis, Biocompatibility, and Cytotoxicity

Graphene, graphene oxide, and reduced graphene oxide have been widely considered as promising candidates for industrial and biomedical applications due to their exceptionally high mechanical stiffness and strength, excellent electrical conductivity, high optical transparency, and good biocompatibility. In this article, we reviewed several techniques that are available for the synthesis of graphene-based nanomaterials, and discussed the biocompatibility and toxicity of such nanomaterials upon exposure to mammalian cells under in vitro and in vivo conditions. Various synthesis strategies have been developed for their fabrication, generating graphene nanomaterials with different chemical and physical properties. As such, their interactions with cells and organs are altered accordingly. Conflicting results relating biocompatibility and cytotoxicity induced by graphene nanomaterials have been reported in the literature. In particular, graphene nanomaterials that are used for in vitro cell culture and in vivo animal models may contain toxic chemical residuals, thereby interfering graphene-cell interactions and complicating interpretation of experimental results. Synthesized techniques, such as liquid phase exfoliation and wet chemical oxidation, often required toxic organic solvents, surfactants, strong acids, and oxidants for exfoliating graphite flakes. Those organic molecules and inorganic impurities that are retained in final graphene products can interact with biological cells and tissues, inducing toxicity or causing cell death eventually. The residual contaminants can cause a higher risk of graphene-induced toxicity in biological cells. This adverse effect may be partly responsible for the discrepancies between various studies in the literature.

Graphene-based nanoplatelets: a new risk to the respiratory system as a consequence of their unusual aerodynamic properties

Graphene is a new nanomaterial with unusual and useful physical and chemical properties. However, in the form of nanoplatelets this new, emerging material could pose unusual risks to the respiratory system after inhalation exposure. The graphene-based nanoplatelets used in this study are commercially available and consist of several sheets of graphene (few-layer graphene). We first derived the respirability of graphene nanoplatelets (GP) from the basic principles of the aerodynamic behavior of plate-shaped particles which allowed us to calculate their aerodynamic diameter. This showed that the nanoplatelets, which were up to 25 μm in diameter, were respirable and so would deposit beyond the ciliated airways following inhalation. We therefore utilized models of pharyngeal aspiration and direct intrapleural installation of GP, as well as an in vitro model, to assess their inflammatory potential. These large but respirable GP were inflammogenic in both the lung and the pleural space. MIP-1α, MCP-1, MIP-2, IL-8, and IL-1β expression in the BAL, the pleural lavage, and cell culture supernatant from THP-1 macrophages were increased with GP exposure compared to controls but not with nanoparticulate carbon black (CB). In vitro, macrophages exposed to GP showed expression of IL-1β. This study highlights the importance of nanoplatelet form as a driver for in vivo and in vitro inflammogenicity by virtue of their respirable aerodynamic diameter, despite a considerable 2-dimensional size which leads to frustrated phagocytosis when they deposit in the distal lungs and macrophages attempt to phagocytose them. Our data suggest that nanoplatelets pose a novel nanohazard and structure-toxicity relationship in nanoparticle toxicology.

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.

Biological interactions of carbon-based nanomaterials: From coronation to degradation

Carbon-based nanomaterials including carbon nanotubes, graphene oxide, fullerenes and nanodiamonds are potential candidates for various applications in medicine such as drug delivery and imaging. However, the successful translation of nanomaterials for biomedical applications is predicated on a detailed understanding of the biological interactions of these materials. Indeed, the potential impact of the so-called bio-corona of proteins, lipids, and other biomolecules on the fate of nanomaterials in the body should not be ignored. Enzymatic degradation of carbon-based nanomaterials by immune-competent cells serves as a special case of bio-corona interactions with important implications for the medical use of such nanomaterials. In the present review, we highlight emerging biomedical applications of carbon-based nanomaterials. We also discuss recent studies on nanomaterial 'coronation' and how this impacts on biodistribution and targeting along with studies on the enzymatic degradation of carbon-based nanomaterials, and the role of surface modification of nanomaterials for these biological interactions.

FROM THE CLINICAL EDITOR

Advances in technology have produced many carbon-based nanomaterials. These are increasingly being investigated for the use in diagnostics and therapeutics. Nonetheless, there remains a knowledge gap in terms of the understanding of the biological interactions of these materials. In this paper, the authors provided a comprehensive review on the recent biomedical applications and the interactions of various carbon-based nanomaterials.

Antiviral Activity of Graphene Oxide: How Sharp Edged Structure and Charge Matter

Graphene oxide and its derivatives have been widely explored for their antimicrobial properties due to their high surface-to-volume ratios and unique chemical and physical properties. However, little information is available on their effects on viruses. In this study, we report the broad-spectrum antiviral activity of GO against pseudorabies virus (PRV, a DNA virus) and porcine epidemic diarrhea virus (PEDV, an RNA virus). Our results showed that GO significantly suppressed the infection of PRV and PEDV for a 2 log reduction in virus titers at noncytotoxic concentrations. The potent antiviral activity of both GO and rGO can be attributed to the unique single-layer structure and negative charge. First, GO exhibited potent antiviral activity when conjugated with PVP, a nonionic polymer, but not when conjugated with PDDA, a cationic polymer. Additionally, the precursors Gt and GtO showed much weaker antiviral activity than monolayer GO and rGO, suggesting that the nanosheet structure is important for antiviral properties. Furthermore, GO inactivated both viruses by structural destruction prior to viral entry. The overall results suggest the potential of graphene oxide as a novel promising antiviral agent with a broad and potent antiviral activity.

Reduced Cytotoxicity of Graphene Nanosheets Mediated by Blood-Protein Coating

The advent and pending wide use of nanoscale materials urges a biosafety assessment and safe design of nanomaterials that demonstrate applicability to human medicine. In biological microenvironment, biomolecules will bind onto nanoparticles forming corona and endow nanoparticles new biological identity. Since blood-circulatory system will most likely be the first interaction organ exposed to these nanomaterials, a deep understanding of the basic interaction mechanisms between serum proteins and foreign nanoparticles may help to better clarify the potential risks of nanomaterials and provide guidance on safe design of nanomaterials. In this study, the adsorption of four high-abundance blood proteins onto the carbon-based nanomaterial graphene oxide (GO) and reduced GO (rGO) were investigated via experimental (AFM, florescence spectroscopy, SPR) and simulation-based (molecular dynamics) approaches. Among the proteins in question, we observe competitive binding to the GO surface that features a mélange of distinct packing modes. Our MD simulations reveal that the protein adsorption is mainly enthalpically driven through strong π-π stacking interactions between GO and aromatic protein residues, in addition to hydrophobic interactions. Overall, these results were in line with previous findings related to adsorption of serum proteins onto single-walled carbon nanotubes (SWCNTs), but GO exhibits a dramatic enhancement of adsorption capacity compared to this one-dimensional carbon form. Encouragingly, protein-coated GO resulted in a markedly less cytotoxicity than pristine and protein-coated SWCNTs, suggesting a useful role for this planar nanomaterial in biomedical applications.

Personalized disease-specific protein corona influences the therapeutic impact of graphene oxide

The hard corona, the protein shell that is strongly attached to the surface of nano-objects in biological fluids, is recognized as the first layer that interacts with biological objects (e.g., cells and tissues). The decoration of the hard corona (i.e., the type, amount, and conformation of the attached proteins) can define the biological fate of the nanomaterial. Recent developments have revealed that corona decoration strongly depends on the type of disease in human patients from which the plasma is obtained as a protein source for corona formation (referred to as the 'personalized protein corona'). In this study, we demonstrate that graphene oxide (GO) sheets can trigger different biological responses in the presence of coronas obtained from various types of diseases. GO sheets were incubated with plasma from human subjects with different diseases/conditions, including hypofibrinogenemia, blood cancer, thalassemia major, thalassemia minor, rheumatism, fauvism, hypercholesterolemia, diabetes, and pregnancy. Identical sheets coated with varying protein corona decorations exhibited significantly different cellular toxicity, apoptosis, and uptake, reactive oxygen species production, lipid peroxidation and nitrogen oxide levels. The results of this report will help researchers design efficient and safe, patient-specific nano biomaterials in a disease type-specific manner for clinical and biological applications.

Low-toxic and safe nanomaterials by surface-chemical design, carbon nanotubes, fullerenes, metallofullerenes, and graphenes

The toxicity grade for a bulk material can be approximately determined by three factors (chemical composition, dose, and exposure route). However, for a nanomaterial it depends on more than ten factors. Interestingly, some nano-factors (like huge surface adsorbability, small size, etc.) that endow nanomaterials with new biomedical functions are also potential causes leading to toxicity or damage to the living organism. Is it possible to create safe nanomaterials if such a number of complicated factors need to be regulated? We herein try to find answers to this important question. We first discuss chemical processes that are applicable for nanosurface modifications, in order to improve biocompatibility, regulate ADME, and reduce the toxicity of carbon nanomaterials (carbon nanotubes, fullerenes, metallofullerenes, and graphenes). Then the biological/toxicological effects of surface-modified and unmodified carbon nanomaterials are comparatively discussed from two aspects: the lowered toxic responses or the enhanced biomedical functions. We summarize the eight biggest challenges in creating low-toxicity and safer nanomaterials and some significant topics of future research needs: to find out safer nanofactors; to establish controllable surface modifications and simpler chemistries for low-toxic nanomaterials; to explore the nanotoxicity mechanisms; to justify the validity of current toxicological theories in nanotoxicology; to create standardized nanomaterials for toxicity tests; to build theoretical models for cellular and molecular interactions of nanoparticles; and to establish systematical knowledge frameworks for nanotoxicology.

Covalent functionalization of graphene oxide with biocompatible poly(ethylene glycol) for delivery of paclitaxel

Graphene oxide (GO), a novel 2D nanomaterial prepared by the oxidation of natural graphite, has been paid much attention in the area of drug delivery due to good biocompatibility and low toxicity. In the present work, 6-armed poly(ethylene glycol) was covalently introduced into the surface of GO sheets via a facile amidation process under mild conditions, making the modified GO, GO-PEG (PEG: 65 wt %, size: 50-200 nm), stable and biocompatible in physiological solution. This nanosized GO-PEG was found to be nontoxic to human lung cancer A549 and human breast cancer MCF-7 cells via cell viability assay. Furthermore, paclitaxel (PTX), a widely used cancer chemotherapy drug, was conjugated onto GO-PEG via π-π stacking and hydrophobic interactions to afford a nanocomplex of GO-PEG/PTX with a relatively high loading capacity for PTX (11.2 wt %). This complex could quickly enter into A549 and MCF-7 cells evidenced by inverted fluorescence microscopy using Fluorescein isothiocyanate as a probe, and it also showed remarkably high cytotoxicity to A549 and MCF-7 cells in a broad range of concentration of PTX and time compared to free PTX. This kind of nanoscale drug delivery system on the basis of PEGylated GO may find potential application in biomedicine.

Protein corona mitigates the cytotoxicity of graphene oxide by reducing its physical interaction with cell membrane

Many recent studies have shown that the way nanoparticles interact with cells and biological molecules can vary greatly in the serum-containing or serum-free culture medium. However, the underlying molecular mechanisms of how the so-called "protein corona" formed in serum medium affects nanoparticles' biological responses are still largely unresolved. Thus, it is critical to understand how absorbed proteins on the surfaces of nanoparticles alter their biological effects. In this work, we have demonstrated with both experimental and theoretical approaches that protein BSA coating can mitigate the cytotoxicity of graphene oxide (GO) by reducing its cell membrane penetration. Our cell viability and cellular uptake experiments showed that protein corona decreased cellular uptake of GO, thus significantly mitigating the potential cytotoxicity of GO. The electron microscopy images also confirmed that protein corona reduced the cellular morphological damage by limiting GO penetration into the cell membrane. Further molecular dynamics (MD) simulations validated the experimental results and revealed that the adsorbed BSA in effect weakened the interaction between the phospholipids and graphene surface due to a reduction of the available surface area plus an unfavorable steric effect, thus significantly reducing the graphene penetration and lipid bilayer damaging. These findings provide new insights into the underlying molecular mechanism of this important graphene protein corona interaction with cell membranes, and should have implications in future development of graphene-based biomedical applications.

Investigation of acute effects of graphene oxide on wastewater microbial community: a case study

The market for graphene-based products, such as graphene oxide (GO), is projected to reach nearly $675 million by 2020, hence it is expected that large quantities of graphene-based wastes will be generated by then. Wastewater treatment plants will be one of the ultimate repositories for these wastes. Efficient waste treatment relies heavily on the functions of diverse microbial communities. Therefore, systematic investigation of any potential toxic effects of GO in wastewater microbial communities is essential to determine the potential adverse effects and the fate of these nanomaterials in the environment. In the present study, we investigate the acute toxicity, i.e. short-term and high load, effect of GO on the microbial functions related to the biological wastewater treatment process. The results showed that toxic effects of GO on microbial communities were dose dependent, especially in concentrations between 50 and 300mg/L. Bacterial metabolic activity, bacterial viability, and biological removal of nutrients, such as organics, nitrogen and phosphorus, were significantly impacted by the presence of GO in the activated sludge. Furthermore, the presence of GO deteriorated the final effluent quality by increasing the water turbidity and reducing the sludge dewaterability. Microscopic techniques confirmed penetration and accumulation of GO inside the activated sludge floc matrix. Results demonstrated that the interaction of GO with wastewater produced significant amount of reactive oxygen species (ROS), which could be one of the responsible mechanisms for the toxic effect of GO.

Synthesis, toxicity, biocompatibility, and biomedical applications of graphene and graphene-related materials

Graphene is a two-dimensional atomic crystal, and since its development it has been applied in many novel ways in both research and industry. Graphene possesses unique properties, and it has been used in many applications including sensors, batteries, fuel cells, supercapacitors, transistors, components of high-strength machinery, and display screens in mobile devices. In the past decade, the biomedical applications of graphene have attracted much interest. Graphene has been reported to have antibacterial, antiplatelet, and anticancer activities. Several salient features of graphene make it a potential candidate for biological and biomedical applications. The synthesis, toxicity, biocompatibility, and biomedical applications of graphene are fundamental issues that require thorough investigation in any kind of applications related to human welfare. Therefore, this review addresses the various methods available for the synthesis of graphene, with special reference to biological synthesis, and highlights the biological applications of graphene with a focus on cancer therapy, drug delivery, bio-imaging, and tissue engineering, together with a brief discussion of the challenges and future perspectives of graphene. We hope to provide a comprehensive review of the latest progress in research on graphene, from synthesis to applications.