Graphene based materials: Past, present and future

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.

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

We developed nanosized, reduced graphene oxide (nano-rGO) sheets with high near-infrared (NIR) light absorbance and biocompatibility for potential photothermal therapy. The single-layered nano-rGO sheets were ∼20 nm in average lateral dimension, functionalized noncovalently by amphiphilic PEGylated polymer chains to render stability in biological solutions and exhibited 6-fold higher NIR absorption than nonreduced, covalently PEGylated nano-GO. Attaching a targeting peptide bearing the Arg-Gly-Asp (RGD) motif to nano-rGO afforded selective cellular uptake in U87MG cancer cells and highly effective photoablation of cells in vitro. In the absence of any NIR irradiation, nano-rGO exhibited little toxicity in vitro at concentrations well above the doses needed for photothermal heating. This work established nano-rGO as a novel photothermal agent due to its small size, high photothermal efficiency, and low cost as compared to other NIR photothermal agents including gold nanomaterials and carbon nanotubes.

https://web.stanford.edu/group/dailab/Reprint/185.%20Ultrasmall%20Reduced%20Graphene%20Oxide%20with%20High%20Near-Infrared%20Absorbance%20for%20Photothermal%20Therapy.pdf

Ultrasmall Reduced Graphene Oxide with High Near-Infrared Absorbance for Photothermal Therapy

Owing to their unique physical and chemical properties, graphene and its derivatives such as graphene oxide (GO), reduced graphene oxide (RGO) and GO-nanocomposites have attracted tremendous interest in many different fields including biomedicine in recent years. With every atom exposed on its surface, single-layered graphene shows ultra-high surface area available for efficient molecular loading and bioconjugation, and has been widely explored as novel nano-carriers for drug and gene delivery. Utilizing the intrinsic near-infrared (NIR) optical absorbance, in vivo graphene-based photothermal therapy has been realized, achieving excellent anti-tumor therapeutic efficacy in animal experiments. A variety of inorganic nanoparticles can be grown on the surface of nano-graphene, obtaining functional graphene-based nanocomposites with interesting optical and magnetic properties useful for multi-modal imaging and imaging-guided cancer therapy. Moreover, significant efforts have also been devoted to study the behaviors and toxicology of functionalized nano-graphene in animals. It has been uncovered that both surface chemistry and sizes play key roles in controlling the biodistribution, excretion, and toxicity of nano-graphene. Biocompatibly coated nano-graphene with ultra-small sizes can be cleared out from body after systemic administration, without rendering noticeable toxicity to the treated mice. In this review article, we will summarize the latest progress in this rapidly growing field, and discuss future prospects and challenges of using graphene-based materials for theranostic applications.

Nano-graphene in biomedicine: theranostic applications

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 ag...

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

In vitro toxicity evaluation of graphene oxide on A549 cells

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

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

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 bact...

Superior Antibacterial Activity of Zinc Oxide/Graphene Oxide Composites Originating from High Zinc Concentration Localized around Bacteria

The protein-nanoparticle (NP) interface is a current frontier of multiple disciplines, full of challenges and opportunities. The unique behaviors of nanomaterials (NMs) bring many exciting applications, and also raise safety concerns. Beyond bioapplications, various NMs could also enter human bodies from the environment. When entering human bodies, NPs interact with various biomolecules, especially proteins, forming a protein corona. This protein-NP complex is what the biosystems 'see' and 'respond to'. Therefore, understanding how NPs interact with proteins is crucial for both bioapplications and the biosafety of NMs. In this review, the current understanding of protein-NP interactions is summarized, including the theoretical background, experimental results, and computational progresses. Guidelines for improving bioapplication performance and reducing the potential biosafety hazard of NMs by designing the protein-NP interactions are discussed, along with future directions and challenges in this exciting field.

Biosafety and Bioapplication of Nanomaterials by Designing Protein–Nanoparticle Interactions

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

Yan-Wen Wang

Papers

In vitro toxicity evaluation of graphene oxide on A549 cells

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

Superior Antibacterial Activity of Zinc Oxide/Graphene Oxide Composites Originating from High Zinc Concentration Localized around Bacteria

Biosafety and Bioapplication of Nanomaterials by Designing Protein–Nanoparticle Interactions

Enhanced bactericidal toxicity of silver nanoparticles by the antibiotic gentamicin