Graphene oxide: a nonspecific enhancer of cellular growth

In vitro and in silico antifungal efficacy of nitrogen-doped carbon nanohorn (NCNH) against Rhizoctonia solani

We have investigated in vitro antifungal efficiency of nitrogen-doped carbon nanohorn (NCNH) against Rhizoctonia solani (R. solani) plant pathogenic fungi. NCNH with size of 50-60 nm and concentrations of 10, 50, 100, and 150 μg mL(-1) were used. The results showed that growth of fungi in the presence of NCNH was significantly (p > .05) inhibited at 150 μg mL(-1) (85.13 ± .97) after 72 h. The results were validated through computational approaches. Molecular docking analysis of NCNH with endochitinase protein of R. solani was performed to validate the potential of antifungal activity of NCNH. Docking results showed different conformations of interaction of NCNH with endochitinase enzyme. The conformation with least binding energy -13.54 kcal/mol was considered further. It is likely that NCNH interacts with the pathogens by mechanically wrapping, which may be one of the major toxicity actions of NCNH against R. solani. The analysis showed that NCNH might interwinds to endochitinase of R. solani leading to the deactivation of the enzyme. To best of our knowledge, this is the first report of antifungal efficacy of NCNH against R. solani and provides useful information about the application of NCNH in resisting crop disease.

Toxicity of graphene oxide on intestinal bacteria and Caco-2 cells

In recent years, novel nanomaterials have received much attention due to their great potential for applications in agriculture, food safety, and food packaging. Among them, graphene and graphene oxide (GO) are emerging as promising nanomaterials that may have a profound impact on food packaging. However, there are some concerns from consumers and the scientific community about the potential toxicity and biocompatibility of nanomaterials. In this study, we investigated the antibacterial properties of GO against human intestinal bacteria. The cytotoxicity of GO was also studied in vitro using the Caco-2 cell line derived from a colon carcinoma. Electron microscopy was used to investigate the morphology of GO and the interaction between GO flakes and Caco-2 cells. GO at different concentrations (10 to 500 μg/ml) exhibited no toxicity against the selected bacteria and a mild cytotoxic action on Caco-2 cells after 24 h of exposure. The results show that weak adsorption of medium nutrients may contribute to GO's low toxicity. This study suggests that GO is biocompatible and has a potential to be used in agriculture and food science, indicating that more studies are needed to exploit its potential applications.

Preparation, characterization, and antibacterial activity of silver nanoparticle-decorated graphene oxide nanocomposite

In this work, we report a facile and green approach to prepare a uniform silver nanoparticles (AgNPs) decorated graphene oxide (GO) nanocomposite (GO-Ag). The nanocomposite was fully characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectra, ultraviolet-visible (UV-vis) absorption spectra, and X-ray photoelectron spectroscopy (XPS), which demonstrated that AgNPs with a diameter of approximately 22 nm were uniformly and compactly deposited on GO. To investigate the silver ion release behaviors, HEPES buffers with different pH (5.5, 7, and 8.5) were selected and the mechanism of release actions was discussed in detail. The cytotoxicity of GO-Ag nanocomposite was also studied using HEK 293 cells. GO-Ag nanocomposite displayed good cytocompatibility. Furthermore, the antibacterial properties of GO-Ag nanocomposite were studied using Gram-negative E. coli ATCC 25922 and Gram-positive S. aureus ATCC 6538 by both the plate count method and disk diffusion method. The nanocomposite showed excellent antibacterial activity. These results demonstrated that GO-Ag nanocomposite, as a kind of antibacterial material, had a great promise for application in a wide range of biomedical applications.

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Stimulated myoblast differentiation on graphene oxide-impregnated PLGA-collagen hybrid fibre matrices

Background

Electrospinning is a simple and effective method for fabricating micro- and nanofiber matrices. Electrospun fibre matrices have numerous advantages for use as tissue engineering scaffolds, such as high surface area-to-volume ratio, mass production capability and structural similarity to the natural extracellular matrix (ECM). Therefore, electrospun matrices, which are composed of biocompatible polymers and various biomaterials, have been developed as biomimetic scaffolds for the tissue engineering applications. In particular, graphene oxide (GO) has recently been considered as a novel biomaterial for skeletal muscle regeneration because it can promote the growth and differentiation of myoblasts. Therefore, the aim of the present study was to fabricate the hybrid fibre matrices that stimulate myoblasts differentiation for skeletal muscle regeneration.

Results

Hybrid fibre matrices composed of poly(lactic-co-glycolic acid, PLGA) and collagen (Col) impregnated with GO (GO-PLGA-Col) were successfully fabricated using an electrospinning process. Our results indicated that the GO-PLGA-Col hybrid matrices were comprised of randomly-oriented continuous fibres with a three-dimensional non-woven porous structure. Compositional analysis showed that GO was dispersed uniformly throughout the GO-PLGA-Col matrices. In addition, the hydrophilicity of the fabricated matrices was significantly increased by blending with a small amount of Col and GO. The attachment and proliferation of the C2C12 skeletal myoblasts were significantly enhanced on the GO-PLGA-Col hybrid matrices. Furthermore, the GO-PLGA-Col matrices stimulated the myogenic differentiation of C2C12 skeletal myoblasts, which was enhanced further under the culture conditions of the differentiation media.

Conclusions

Taking our findings into consideration, it is suggested that the GO-PLGA-Col hybrid fibre matrices can be exploited as potential biomimetic scaffolds for skeletal tissue engineering and regeneration because these GO-impregnated hybrid matrices have potent effects on the induction of spontaneous myogenesis and exhibit superior bioactivity and biocompatibility.

Interaction of graphene family materials with Listeria monocytogenes and Salmonella enterica

Graphene family materials have unique properties, which make them valuable for a range of applications. The antibacterial properties of graphene have been reported; however, findings have been contradictory. This study reports on the antimicrobial proprieties of three different graphene materials (pristine graphene (pG), graphene oxide (GO), and reduced graphene oxide (rGO)) against the food-borne bacterial pathogens Listeria monocytogenes and Salmonella enterica. A high concentration (250 μg/mL) of all the analyzed graphenes completely inhibited the growth of both pathogens, despite their difference in bacterial cell wall structure. At a lower concentration (25 μg/mL), similar effects were only observed with GO, as growth inhibition decreased with pG and rGO at the lower concentration. Interaction of the nanoparticles with the pathogenic bacteria was found to differ depending on the form of graphene. Microscopic imaging demonstrated that bacteria were arranged at the edges of pG and rGO, while with GO, they adhered to the nanoparticle surface. GO was found to have the highest antibacterial activity.

Dry transfer of chemical-vapor-deposition-grown graphene onto liquid-sensitive surfaces for tunnel junction applications

We report a dry transfer method that can tranfer chemical vapor deposition (CVD) grown graphene onto liquid-sensitive surfaces. The graphene grown on copper (Cu) foil substrate was first transferred onto a freestanding 4 μm thick sputtered Cu film using the conventional wet transfer process, followed by a dry transfer process onto the target surface using a polydimethylsiloxane stamp. The dry-transferred graphene has similar properties to traditional wet-transferred graphene, characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and electrical transport measurements. It has a sheet resistance of 1.6 ∼ 3.4 kΩ/□, hole density of (4.1 ∼ 5.3) × 10(12) cm(-2), and hole mobility of 460 ∼ 760 cm(2) V(-1) s(-1) without doping at room temperature. The results suggest that large-scale CVD-grown graphene can be transferred with good quality and without contaminating the target surface by any liquid. Mg/MgO/graphene tunnel junctions were fabricated using this transfer method. The junctions show good tunneling characteristics, which demonstrates the transfer technique can also be used to fabricate graphene devices on liquid-sensitive surfaces.

Microencapsulation of bacterial strains in graphene oxide nano-sheets using vortex fluidics

Microencapsulation of bacterial cells with different shapes in graphene oxide (GO) layers is effective using a vortex fluidic device, with the bacterial cells showing restricted cellular growth with their biological activity sustained.

Graphene oxide as electron shuttle for increased redox conversion of contaminants under methanogenic and sulfate-reducing conditions

Graphene oxide (GO) is reported for the first time as electron shuttle to increase the redox conversion of the azo compound, reactive red 2 (RR2, 0.5mM), and the nitroaromatic, 3-chloronitrobenzene (3CNB, 0.5mM). GO (5mgL(-1)) increased 10-fold and 7.6-fold the reduction rate of RR2 and 3CNB, respectively, in abiotic incubations with sulfide (2.6mM) as electron donor. GO also increased by 2-fold and 3.6-fold, the microbial reduction rate of RR2 by anaerobic sludge under methanogenic and sulfate-reducing conditions, respectively. Deep characterization of GO showed that it has a proper size distribution (predominantly between 450 and 700nm) and redox potential (+50.8mV) to promote the reduction of RR2 and 3CNB. Further analysis revealed that biogenic sulfide plays a major role on the GO-mediated reduction of RR2. GO is proposed as an electron shuttle to accelerate the redox conversion of recalcitrant pollutants, such as nitro-benzenes and azo dyes.

Efficient photothermal therapy of brain cancer through porphyrin functionalized graphene oxide

High photothermal therapy efficiency is achieved by using an 808 nm laser to irradiate 87-MG cells co-cultured with porphyrin functionalized graphene oxide.

Graphene oxide nanoparticle attachment and its toxicity on living lung epithelial cells

Since its discovery graphene and its oxidized form graphene oxide have attracted interest in a wide range of applications, which calls for scrutinized studies about their possible toxicity.

Electrospinning thermoplastic polyurethane/graphene oxide scaffolds for small diameter vascular graft applications

Fabrication of small diameter vascular grafts plays an important role in vascular tissue engineering. In this study, thermoplastic polyurethane (TPU)/graphene oxide (GO) scaffolds were fabricated via electrospinning at different GO contents as potential candidates for small diameter vascular grafts. In terms of mechanical and surface properties, the tensile strength, Young's modulus, and hydrophilicity of the scaffolds increased with an increase of GO content while plasma treatment dramatically improved the scaffold hydrophilicity. Mouse fibroblast (3T3) and human umbilical vein endothelial cells (HUVECs) were cultured on the scaffolds separately to study their biocompatibility and potential to be used as vascular grafts. It was found that cell viability for both types of cells, fibroblast proliferation, and HUVEC attachment were the highest at a 0.5wt.% GO loading whereas oxygen plasma treatment also enhanced HUVEC viability and attachment significantly. In addition, the suture retention strength and burst pressure of tubular TPU/GO scaffolds containing 0.5wt.% GO were found to meet the requirements of human blood vessels, and endothelial cells were able to attach to the inner surface of the tubular scaffolds. Platelet adhesion tests using mice blood indicated that vascular scaffolds containing 0.5% GO had low platelet adhesion and activation. Therefore, the electrospun TPU/GO tubular scaffolds have the potential to be used in vascular tissue engineering.

Migration of silver nanoparticles from silver decorated graphene oxide to other carbon nanostructures

Decoration of graphene oxide (GO) sheets with Ag nanoparticles has been demonstrated using a simple sonication technique. By changing the ratio between Ag-decorated-GO and GO, a series of Ag-decorated-GO samples with different Ag loadings were synthesized. These Ag-decorated-GO samples were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD) spectroscopy, thermal gravimetric analysis (TGA), and differential scanning calorimetric (DSC) techniques. TEM analysis showed that Ag nanoparticles were evenly distributed on GO sheets, and the size analysis of the particles using multiple TEM images indicated that Ag nanoparticles have an average size of 6-7 nm. TEM analysis also showed that Ag nanoparticles migrated from Ag-decorated-GO to later-added GO sheets. In XRD, all the Ag-decorated GO samples showed the characteristic peaks related to GO and face-centered-cubic (fcc) Ag. Thermal analysis showed peaks related to the combustion of graphitic carbon shifted to lower temperatures after GO sheets were decorated with Ag nanoparticles. In addition, further experiments performed using Ag-decorated-GO and multiwalled carbon nanotubes (MWNTs) confirmed that Ag nanoparticles migrated from Ag-decorated-GO to later-added carbon nanotubes without a noticeable coalescence of Ag nanoparticles.

Graphene oxide amplifies the phytotoxicity of arsenic in wheat

Graphene oxide (GO) is widely used in various fields and is considered to be relatively biocompatible. Herein, "indirect" nanotoxicity is first defined as toxic amplification of toxicants or pollutants by nanomaterials. This work revealed that GO greatly amplifies the phytotoxicity of arsenic (As), a widespread contaminant, in wheat, for example, causing a decrease in biomass and root numbers and increasing oxidative stress, which are thought to be regulated by its metabolisms. Compared with As or GO alone, GO combined with As inhibited the metabolism of carbohydrates, enhanced amino acid and secondary metabolism and disrupted fatty acid metabolism and the urea cycle. GO also triggered damage to cellular structures and electrolyte leakage and enhanced the uptake of GO and As. Co-transport of GO-loading As and transformation of As(V) to high-toxicity As(III) by GO were observed. The generation of dimethylarsinate, produced from the detoxification of inorganic As, was inhibited by GO in plants. GO also regulated phosphate transporter gene expression and arsenate reductase activity to influence the uptake and transformation of As, respectively. Moreover, the above effects of GO were concentration dependent. Given the widespread exposure to As in agriculture, the indirect nanotoxicity of GO should be carefully considered in food safety.

Availability of the basal planes of graphene oxide determines whether it is antibacterial

There are significant controversies on the antibacterial properties of graphene oxide (GO): GO was reported to be bactericidal in saline, whereas its activity in nutrient broth was controversial. To unveil the mechanisms underlying these contradictions, we performed antibacterial assays under comparable conditions. In saline, bare GO sheets were intrinsically bactericidal, yielding a bacterial survival percentage of <1% at 200 μg/mL. Supplementing saline with ≤10% Luria-Bertani (LB) broth, however, progressively deactivated its bactericidal activity depending on LB-supplementation ratio. Supplementation of 10% LB made GO completely inactive; instead, ∼100-fold bacterial growth was observed. Atomic force microscopy images showed that certain LB components were adsorbed on GO basal planes. Using bovine serum albumin and tryptophan as well-defined model adsorbates, we found that noncovalent adsorption on GO basal planes may account for the deactivation of GO's bactericidal activity. Moreover, this deactivation mechanism was shown to be extrapolatable to GO's cytotoxicity against mammalian cells. Taken together, our observations suggest that bare GO intrinsically kills both bacteria and mammalian cells and noncovalent adsorption on its basal planes may be a global deactivation mechanism for GO's cytotoxicity.

Synergistic acceleration in the osteogenesis of human mesenchymal stem cells by graphene oxide-calcium phosphate nanocomposites

Nanocomposites consisting of oblong ultrathin plate shaped calcium phosphate nanoparticles and graphene oxide microflakes were synthesized and have demonstrated markedly synergistic effect in accelerating stem cell differentiation to osteoblasts.

Comparative study of bioactivity of collagen scaffolds coated with graphene oxide and reduced graphene oxide

Background

Graphene oxide (GO) is a single layer carbon sheet with a thickness of less than 1 nm. GO has good dispersibility due to surface modifications with numerous functional groups. Reduced graphene oxide (RGO) is produced via the reduction of GO, and has lower dispersibility. We examined the bioactivity of GO and RGO films, and collagen scaffolds coated with GO and RGO.

Methods

GO and RGO films were fabricated on a culture dish. Some GO films were chemically reduced using either ascorbic acid or sodium hydrosulfite solution, resulting in preparation of RGO films. The biological properties of each film were evaluated by scanning electron microscopy (SEM), atomic force microscopy, calcium adsorption tests, and MC3T3-E1 cell seeding. Subsequently, GO- and RGO-coated collagen scaffolds were prepared and characterized by SEM and compression tests. Each scaffold was implanted into subcutaneous tissue on the backs of rats. Measurements of DNA content and cell ingrowth areas of implanted scaffolds were performed 10 days post-surgery.

Results

The results show that GO and RGO possess different biological properties. Calcium adsorption and alkaline phosphatase activity were strongly enhanced by RGO, suggesting that RGO is effective for osteogenic differentiation. SEM showed that RGO-modified collagen scaffolds have rough, irregular surfaces. The compressive strengths of GO- and RGO-coated scaffolds were approximately 1.7-fold and 2.7-fold greater, respectively, when compared with the non-coated scaffold. Tissue ingrowth rate was 39% in RGO-coated scaffolds, as compared to 20% in the GO-coated scaffold and 16% in the non-coated scaffold.

Conclusion

In summary, these results suggest that GO and RGO coatings provide different biological properties to collagen scaffolds, and that RGO-coated scaffolds are more bioactive than GO-coated scaffolds.

Assessing in vivo toxicity of graphene materials: current methods and future outlook

Graphene, a novel 2D carbon nanomaterial with unique properties, has attracted massive attention. Evaluating its toxicity is of great significance due to its potential applications in many fields, especially in biomedicine. In this review, the toxicity of graphene-based nanomaterials (GNMs) and related mechanisms at the molecular and cellular level, various approaches to evaluation of the in vivo toxicity of GNMs and major factors defining their toxicity will be discussed and summarized. This review will allow better understanding of the in vitro and in vivo toxicity of GNMs, which, we believe, may facilitate design and fabrication of novel, biocompatible and efficient GNM-based systems for biomedical applications.

Graphene-based nanocomposite as an effective, multifunctional, and recyclable antibacterial agent

The development of new antibacterial agents that are highly effective are of great interest. Herein, we present a recyclable and synergistic nanocomposite by growing both iron oxide nanoparticles (IONPs) and silver nanoparticles (AgNPs) on the surface of graphene oxide (GO), obtaining GO-IONP-Ag nanocomposite as a novel multifunctional antibacterial material. Compared with AgNPs, which have been widely used as antibacterial agents, our GO-IONP-Ag shows much higher antibacterial efficiency toward both Gram-negative bacteria Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus). Taking the advantage of its strong near-infrared (NIR) absorbance, photothermal treatment is also conducted with GO-IONP-Ag, achieving a remarkable synergistic antibacterial effect to inhibit S. aureus at a rather low concentration of this agent. Moreover, with magnetic IONPs existing in the composite, we can easily recycle GO-IONP-Ag by magnetic separation, allowing its repeated use. Given the above advantages as well as its easy preparation and cheap cost, GO-IONP-Ag developed in this work may find potential applications as a useful antibacterial agent in the areas of healthcare and environmental engineering.

Delivery of bone morphogenetic protein-2 and substance P using graphene oxide for bone regeneration

In this study, we demonstrate that graphene oxide (GO) can be used for the delivery of bone morphogenetic protein-2 (BMP-2) and substance P (SP), and that this delivery promotes bone formation on titanium (Ti) implants that are coated with GO. GO coating on Ti substrate enabled a sustained release of BMP-2. BMP-2 delivery using GO-coated Ti exhibited a higher alkaline phosphatase activity in bone-forming cells in vitro compared with bare Ti. SP, which is known to recruit mesenchymal stem cells (MSCs), was co-delivered using Ti or GO-coated Ti to further promote bone formation. SP induced the migration of MSCs in vitro. The dual delivery of BMP-2 and SP using GO-coated Ti showed the greatest new bone formation on Ti implanted in the mouse calvaria compared with other groups. This approach may be useful to improve osteointegration of Ti in dental or orthopedic implants.

Morphology change and detachment of lipid bilayers from the mica substrate driven by graphene oxide sheets

Understanding the interaction between graphene oxide (GO) and a lipid membrane is significant for exploring the biocompatibility and cytotoxicity of GO, which is the basis for utilizing GO in the fields of biosensors, bioimaging, drug delivery, antibacterials, and so on. In this article, we monitored the dynamic process of the morphology change and detachment of lipid bilayers on mica substrates prompted by GO sheets by in situ atomic force microscope (AFM) imaging. It was found that the bare lipid bilayer dramatically expanded in height and would be unstable and detachable from the mica substrates as induced by GO. The detached lipid molecules were found to bind to the GO surface. The results also imply that GO is likely to influence the height and stability of the supported lipid bilayers (SLBs) by adsorbing metal ions such as calcium ions that were used to stabilize the bilayer structures on the mica substrate. These findings illustrate a complicated effect of GO on the SLBs and should be helpful in future applications of GO in biotechnology.

Simulation and analysis of cellular internalization pathways and membrane perturbation for graphene nanosheets

Clarifying the mechanisms of cellular interactions of graphene family nanomaterials is an urgent issue to the development of guidelines for safer biomedical applications and to the evaluation of health and environment impacts. By combining large-scale computer simulations, theoretical analysis, and experimental discussions, here we present a systematic study on the interactions of graphene nanosheets having various oxidization degrees with a model lipid bilayer membrane. In the mesoscopic simulations, we investigate the detailed translocation pathways of these materials across a 56 × 56 nm(2) membrane patch which allows us to fully consider the role of membrane perturbation during this process. A phase diagram regarding the transmembrane translocation mechanisms of graphene nanosheets is thereby obtained in the space of oxidization degree and particle size. Then, we propose a theoretical approach to analyze the effects of various initial equilibrium states of graphene nanosheets with membrane on their following cellular uptake process. Finally, we demonstrate that the simulation and theoretical results reproduce some important experimental findings towards the mechanisms of cytotoxicity and antibacterial activity of graphene materials. These results not only provide new insight into the cellular internalization mechanism of graphene-based nanomaterials but also offer fundamental understanding on their physicochemical properties which can be precisely tailored for safer biomedical and environment applications.

Highly active bidirectional electron transfer by a self-assembled electroactive reduced-graphene-oxide-hybridized biofilm

Low extracellular electron transfer performance is often a bottleneck in developing high-performance bioelectrochemical systems. Herein, we show that the self-assembly of graphene oxide and Shewanella oneidensis MR-1 formed an electroactive, reduced-graphene-oxide-hybridized, three-dimensional macroporous biofilm, which enabled highly efficient bidirectional electron transfers between Shewanella and electrodes owing to high biomass incorporation and enhanced direct contact-based extracellular electron transfer. This 3D electroactive biofilm delivered a 25-fold increase in the outward current (oxidation current, electron flux from bacteria to electrodes) and 74-fold increase in the inward current (reduction current, electron flux from electrodes to bacteria) over that of the naturally occurring biofilms.

Assessment of the toxic potential of graphene family nanomaterials

Graphene, a single-atom-thick carbon nanosheet, has attracted great interest as a promising nanomaterial for a variety of bioapplications because of its extraordinary properties. However, the potential for widespread human exposure raises safety concerns about graphene and its derivatives, referred to as graphene-family nanomaterials. This review summarizes recent findings on the toxicological effects and the potential toxicity mechanisms of graphene-family nanomaterials in bacteria, mammalian cells, and animal models. Graphene, graphene oxide, and reduced graphene oxide elicit toxic effects both in vitro and in vivo, whereas surface modifications can significantly reduce their toxic interactions with living systems. Standardization of terminology and the fabrication methods of graphene-family nanomaterials are warranted for further investigations designed to decrease their adverse effects and explore their biomedical applications.

Quantum dot conjugated S. cerevisiae as smart nanotoxicity indicators for screening the toxicity of nanomaterials

Quantum dot conjugatedS. cerevisiaeas smart nanotoxicity indicators for screening the toxicity of nanomaterials.

Graphene oxide incorporated collagen–fibrin biofilm as a wound dressing material

GO was incorporated in the collagen and fibrin composite film (CFGO), these films were used as wound dressing material on the experimental wounds of rats and the efficacy of CFGO was studied using conventional methods (schematic illustration).

Graphene oxide as a nanocarrier for gramicidin (GOGD) for high antibacterial performance

As a powerful and novel nanocarrier, graphene oxide (GO) is employed to load a water insoluble antibacterial drug, gramicidin (GD), for effective antibacterial treatments.

Graphene oxide doped conducting polymer nanocomposite film for electrode-tissue interface

One of the most significant components for implantable bioelectronic devices is the interface between the microelectrodes and the tissue or cells for disease diagnosis or treatment. To make the devices work efficiently and safely in vivo, the electrode-tissue interface should not only be confined in micro scale, but also possesses excellent electrochemical characteristic, stability and biocompatibility. Considering the enhancement of many composite materials by combining graphene oxide (GO) for its multiple advantages, we dope graphene oxide into poly(3,4-ethylenedioxythiophene) (PEDOT) forming a composite film by electrochemical deposition for electrode site modification. As a consequence, not only the enlargement of efficient surface area, but also the development of impedance, charge storage capacity and charge injection limit contribute to the excellent electrochemical performance. Furthermore, the stability and biocompatibility are confirmed by numerously repeated usage test and cell proliferation and attachment examination, respectively. As electrode-tissue interface, this biomaterial opens a new gate for tissue engineering and implantable electrophysiological devices.

Photoresponsive fluorescent reduced graphene oxide by spiropyran conjugated hyaluronic acid for in vivo imaging and target delivery

This present article demonstrates the strategy to prepare photoresponsive reduced graphene oxide with mussel inspired adhesive material dopamine (DN) and photochromic dye spiropyran (SP) conjugated to the backbone of the targeting ligand hyaluronic acid (HA; HA-SP). Graphene oxide (GO) was reduced by prepared HA-SP accepting the advantages of catechol chemistry under mildly alkaline condition enabling to achieve functionalized graphene (rGO/HA-SP) as fluorescent nanoparticles. Due to containing HA, rGO/HA-SP can bind to the CD44 cell receptors. The prepared rGO/HA-SP is able to retain its photochromic features and can be converted to merocyanine (MC) form upon irradiation with UV light (wavelength: 365 nm) displaying purple color. Photochromic behavior of rGO/HA-SP was monitored by UV-vis and fluorescence spectroscopy. In vitro fluorescence behavior, examined by confocal laser scanning microscope (CLSM), of rGO/HA-SP in cancerous A549 cell lines assured that efficient delivery of rGO/HA-SP was gained due to HA as targeting ligand. In this work, we have shown that in vivo fluorescence image of spiropyran is possible by administrating MC form solution of rGO/HA-SP using Balb/C mice as in vivo modal. Accumulation of rGO/HA-SP in tumor tissue from biodistribution analysis strongly supports the specific delivery of prepared graphene to the target destination. The well tuned drug release manner from the surface of rGO/HA-SP strongly recommends the developed material not only as fluorescent probe for diagnosis but also as a drug carrier in drug delivery system.

Biomedical applications of graphene and graphene oxide

Graphene has unique mechanical, electronic, and optical properties, which researchers have used to develop novel electronic materials including transparent conductors and ultrafast transistors. Recently, the understanding of various chemical properties of graphene has facilitated its application in high-performance devices that generate and store energy. Graphene is now expanding its territory beyond electronic and chemical applications toward biomedical areas such as precise biosensing through graphene-quenched fluorescence, graphene-enhanced cell differentiation and growth, and graphene-assisted laser desorption/ionization for mass spectrometry. In this Account, we review recent efforts to apply graphene and graphene oxides (GO) to biomedical research and a few different approaches to prepare graphene materials designed for biomedical applications. Because of its excellent aqueous processability, amphiphilicity, surface functionalizability, surface enhanced Raman scattering (SERS), and fluorescence quenching ability, GO chemically exfoliated from oxidized graphite is considered a promising material for biological applications. In addition, the hydrophobicity and flexibility of large-area graphene synthesized by chemical vapor deposition (CVD) allow this material to play an important role in cell growth and differentiation. The lack of acceptable classification standards of graphene derivatives based on chemical and physical properties has hindered the biological application of graphene derivatives. The development of an efficient graphene-based biosensor requires stable biofunctionalization of graphene derivatives under physiological conditions with minimal loss of their unique properties. For the development graphene-based therapeutics, researchers will need to build on the standardization of graphene derivatives and study the biofunctionalization of graphene to clearly understand how cells respond to exposure to graphene derivatives. Although several challenging issues remain, initial promising results in these areas point toward significant potential for graphene derivatives in biomedical research.

Anti-adhesion and antibacterial activity of silver nanoparticles supported on graphene oxide sheets

This work reports on the preparation, characterization and antibacterial activity of a nanocomposite formed from graphene oxide (GO) sheets decorated with silver nanoparticles (GO-Ag). The GO-Ag nanocomposite was prepared in the presence of AgNO3 and sodium citrate. The physicochemical characterization was performed by UV-vis spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM). The average size of the silver nanoparticles anchored on the GO surface was 7.5 nm. Oxidation debris fragments (a byproduct adsorbed on the GO surface) were found to be crucial for the nucleation and growth of the silver nanoparticles. The antibacterial activity of the GO and GO-Ag nanocomposite against the microorganism Pseudomonas aeruginosa was investigated using the standard counting plate methodology. The GO dispersion showed no antibacterial activity against P. aeruginosa over the concentration range investigated. On the other hand, the GO-Ag nanocomposite displayed high biocidal activity with a minimum inhibitory concentration ranging from 2.5 to 5.0 μg/mL. The anti-biofilm activity toward P. aeruginosa adhered on stainless steel surfaces was also investigated. The results showed a 100% inhibition rate of the adhered cells after exposure to the GO-Ag nanocomposite for one hour. To the best of our knowledge, this work provides the first direct evidence that GO-Ag nanocomposites can inhibit the growth of microbial adhered cells, thus preventing the process of biofilm formation. These promising results support the idea that GO-Ag nanocomposites may be applied as antibacterial coatings material to prevent the development of biofilms in food packaging and medical devices.