Graphene-related Nanomaterials Research Articles

Graphene-Related Nanomaterials for Biomedical Applications

This paper builds on the context and recent progress on the control, reproducibility, and limitations of using graphene and graphene-related materials (GRMs) in biomedical applications. The review describes the human hazard assessment of GRMs in in vitro and in vivo studies, highlights the composition-structure-activity relationships that cause toxicity for these substances, and identifies the key parameters that determine the activation of their biological effects. GRMs are designed to offer the advantage of facilitating unique biomedical applications that impact different techniques in medicine, especially in neuroscience. Due to the increasing utilization of GRMs, there is a need to comprehensively assess the potential impact of these materials on human health. Various outcomes associated with GRMs, including biocompatibility, biodegradability, beneficial effects on cell proliferation, differentiation rates, apoptosis, necrosis, autophagy, oxidative stress, physical destruction, DNA damage, and inflammatory responses, have led to an increasing interest in these regenerative nanostructured materials. Considering the existence of graphene-related nanomaterials with different physicochemical properties, the materials are expected to exhibit unique modes of interactions with biomolecules, cells, and tissues depending on their size, chemical composition, and hydrophil-to-hydrophobe ratio. Understanding such interactions is crucial from two perspectives, namely, from the perspectives of their toxicity and biological uses. The main aim of this study is to assess and tune the diverse properties that must be considered when planning biomedical applications. These properties include flexibility, transparency, surface chemistry (hydrophil-hydrophobe ratio), thermoelectrical conductibility, loading and release capacity, and biocompatibility.

Surface chemistry of graphene tailoring the activity of digestive enzymes by modulating interfacial molecular interactions

As a kind of novel functional material, graphene-related nanomaterials (GRMs) have great potentials in industrial and biomedical applications. Meanwhile, the production and wide application of GRMs will increase the risk of unintended or intentional oral exposure to human beings, attracting safety concerns about their biological fates and toxicological effects. The normal enzymatic activity of digestive enzymes is essential for the proper functioning of the gastrointestinal tract system. However, whether and how orally entered GRMs and their surface groups affect digestive enzymes’ activity are still scarce. In this paper, we systematically studied the effects of graphene oxide (GO), graphene modified with hydroxyl groups (OH-G), carboxyl groups (COOH-G), and amino groups (NH2-G) on enzymatic activity of three typical digestive enzymes (pepsin, trypsin, and α-pancreatic amylase). The results showed that the activity of trypsin and α-pancreatic amylase could be greatly changed after GRMs incubation in a surface chemistry dependent manner, while the activity of pepsin was not affected. To elucidate the mechanisms at the molecular level, the interactions between trypsin and GRMs were studied by spectrometry, thermophoresis, and computational simulation approaches, and the key roles of surface chemistry of GRMs in tailoring the activity of trypsin were finally figured out. GO allosterically inhibited trypsin’s activity in the non-competitive manner because of the conformation transition induced by the intensive interactions. COOH-G could effectively hamper enzymatic activity of trypsin in the competitive manner by blocking the active catalytic pocket. As for NH2-G and OH-G, they had little impact on the activity of trypsin due to the weak binding affinity or limited conformational change. Our findings not only indicate surface chemistry plays an important role in tailoring the effects of GRMs on the activity of digestive enzymes but also provide new insights for understanding the oral safety of nanomaterials from daily products and the environment.

Graphene, an Interesting Nanocarbon Allotrope for Biosensing Applications: Advances, Insights, and Prospects

Graphene, a relatively new two-dimensional (2D) nanomaterial, possesses unique structure (e.g. lighter, harder, and more flexible than steel) and tunable physicochemical (e.g. electronical, optical) properties with potentially wide eco-friendly and cost-effective usage in biosensing. Furthermore, graphene-related nanomaterials (e.g. graphene oxide, doped graphene, carbon nanotubes) have inculcated tremendous interest among scientists and industrials for the development of innovative biosensing platforms, such as arrays, sequencers and other nanooptical/biophotonic sensing systems (e.g. FET, FRET, CRET, GERS). Indeed, combinatorial functionalization approaches are constantly improving the overall properties of graphene, such as its sensitivity, stability, specificity, selectivity, and response for potential bioanalytical applications. These include real-time multiplex detection, tracking, qualitative, and quantitative characterization of molecules (i.e. analytes [H2O2, urea, nitrite, ATP or NADH]; ions [Hg2+, Pb2+, or Cu2+]; biomolecules (DNA, iRNA, peptides, proteins, vitamins or glucose; disease biomarkers such as genetic alterations in BRCA1, p53) and cells (cancer cells, stem cells, bacteria, or viruses). However, there is still a paucity of comparative reports that critically evaluate the relative toxicity of carbon nanoallotropes in humans. This manuscript comprehensively reviews the biosensing applications of graphene and its derivatives (i.e. GO and rGO). Prospects and challenges are also introduced.

Nonradiative Excited-State Decay via Conical Intersection in Graphene Nanostructures.

Chemical groups are known to tune the luminescent efficiencies of graphene-related nanomaterials, but some species, including the epoxide group (-COC-), are suspected to act as emission-quenching sites. Herein, by performing nonadiabatic excited-state dynamics simulations, we reveal a fast (within 300 fs) nonradiative excited-state decay of a graphene epoxide nanostructure from the lowest excited singlet (S1 ) state to the ground (S0 ) state via a conical intersection (CI), at which the energy difference between the S1 and S0 states is approximately zero. This CI is induced after breaking one C-O bond at the -COC- moiety during excited-state structural relaxation. This study ascertains the role of epoxide groups in inducing the nonradiative recombination of the excited electron-hole, providing important insights into the CI-promoted nonradiative de-excitations and the luminescence tuning of relevant materials. In addition, it shows the feasibility of utilizing nonadiabatic excited-state dynamics simulations to investigate the photophysical processes of the excited states of graphene nanomaterials.

Graphene and Graphene-Based Nanomaterials for DNA Detection: A Review.

DNA detection with high sensitivity and specificity has tremendous potential as molecular diagnostic agents. Graphene and graphene-based nanomaterials, such as graphene nanopore, graphene nanoribbon, graphene oxide, and reduced graphene oxide, graphene-nanoparticle composites, were demonstrated to have unique properties, which have attracted increasing interest towards the application of DNA detection with improved performance. This article comprehensively reviews the most recent trends in DNA detection based on graphene and graphene-related nanomaterials. Based on the current understanding, this review attempts to identify the future directions in which the field is likely to thrive, and stimulate more significant research in this subject.

Understanding the Roles of Solution Chemistries and Functionalization on the Aggregation of Graphene-Based Nanomaterials Using Molecular Dynamic Simulations

Microscopic aggregation processes of graphene-related nanomaterials (GNs) (including graphene, graphene oxide, carbon nanotubes, carboxylic carbon nanotubes, fullerene, and fullerol) were explored by molecular dynamic (MD) simulations. The aggregation exhibited a strong dependence on solution chemistries and the presence of oxygen-containing functional groups, and the mechanisms were uncovered. The aggregate configurations observed in MD simulations were consistent with the results obtained using density functional theory calculations. Upon the aggregation, the configurations of the GNs were changed, and the electrical properties were affected. The statistics of the Brownian trajectories of the GNs were investigated and were found to vary in the presence of oxygen-containing functional groups and the pH conditions. In addition, the aggregation behavior of GNs was found to be size- and density-dependent, with the density affecting the aggregation efficiency and the size of the nanostructure. Overall, our s...

Strong hydrophobic interaction between graphene oxide and supported lipid bilayers revealed by AFM.

Understanding the interaction between graphene oxide (GO) and lipid membranes is of great importance for its various applications in biotechnology. Here, we investigated the interaction between GO and charged supported lipid bilayers (SLBs) by in situ atomic force microscope (AFM) imaging. It was found that GO could peel off a single layer of positively charged SLBs and deposited on the hydrophobic part of the remaining sublayer. Then free lipid molecules would assemble on GO surface and formed 1.5 bilayers in a lipid-GO-lipid manner. For negatively charged lipid bilayers, however, GO deposited to the SLBs only when its concentration was very high. These results indicate that, in addition to electrostatic interaction, the hydrophobic interaction plays an important role when GO sheets deposit onto the charged lipid bilayers, and should be helpful to understand possible cytotoxicity and antibiosis of graphene-related nanomaterials. Microsc. Res. Tech. 79:721-726, 2016. © 2016 Wiley Periodicals, Inc.

Production of quasi-2D graphene nanosheets through the solvent exfoliation of pitch-based carbon fiber

Stable dispersion of quasi-2D graphene sheets with a concentration up to 1.27 mg mL−1 was prepared by sonication-assisted solvent exfoliation of pitch-based carbon fiber in N-methyl pyrrolidone with the mass yield of 2.32%. Prepared quasi-2D graphene sheets have multi-layered 2D plate-like morphology with rich inclusions of graphitic carbons, a low number of structural defects, and high dispersion stability in aprotic polar solvents, and facilitate the utilization of quasi-2D graphene sheets prepared from pitch-based carbon fiber for various electronic and structural applications. Thin films of quasi-2D graphene sheets prepared by vacuum filtration of the dispersion of quasi-2D graphene sheets demonstrated electrical conductivity up to 1.14 × 104 Ω/□ even without thermal treatment, which shows that pitch-based carbon fiber might be useful as the source of graphene-related nanomaterials. Because pitch-based carbon fiber could be prepared from petroleum pitch, a very cheap structural material for the pavement of asphalt roads, our approach might be promising for the mass production of quasi-2D graphene nanomaterials.

Cytotoxicity Profile of Highly Hydrogenated Graphene

Graphene and its graphene-related counterparts have been considered the future of advanced nanomaterials owing to their exemplary properties. An increase in their potential applications in the biomedical field has led to serious concerns regarding their safety and impact on health. To understand the toxicity profile for a particular type of graphene utilized in a given application, it is important to recognize the differences between the graphene-related components and correlate their cellular toxicity effects to the attributed physiochemical properties. In this study, the cytoxicity effects of highly hydrogenated graphene (HHG) and its graphene oxide (GO) counterpart on the basis of in vitro toxicological assessments are reported and the effects correlated with the physiochemical properties of the tested nanomaterials. Upon 24 h exposure to the nanomaterials, a dose-dependent cellular cytotoxic effect was exhibited and the HHG was observed to be more cytotoxic than its GO control. Detailed characterization revealed an extensive C-H sp(3) network on the carbon backbone of HHG with few oxygen-containing groups, as opposed to the presence of large amounts of oxygen-containing groups on the GO. It is therefore hypothesized that the preferential adsorption of micronutrients on the surface of the HHG nanomaterial by means of hydrophobic interactions resulted in a reduction in the bioavailability of nutrients required for cellular viability. The nanotoxicological profile of highly hydrogenated graphene is assessed for the first time in our study, thereby paving the way for further evaluation of the toxicity risks involved with the utilization of various graphene-related nanomaterials in the real world.

Single-pass kelvin force microscopy and dC/dZ imaging: applications for graphene-related nanomaterials

Development of advanced imaging strategies that could either expand the breadth of what is measurable in material science or break the current limits on detection sensitivity and spatial resolution is highly desired for atomic force microscopy (AFM)-associated metrology. We report that single-pass Kelvin force microscopy (KFM) and capacitance gradient (dC/dZ) imaging can be performed in the intermittent contact regime, and it allows simultaneous acquisition of a sample's morphology as well as its two distinctive electric properties with nanometer-scale spatial resolution. Applications of this technique for enhanced sensing of graphene will be presented.

The Toxicity of Graphene Oxides: Dependence on the Oxidative Methods Used

Graphene, a class of two-dimensional carbon nanomaterial, has attracted extensive interest in recent years, with a significant amount of research focusing on graphene oxides (GOs). They have been primed as potential candidates for biomedical applications such as cell labeling and drug delivery, thus the toxicity and behavior of graphene oxides in biological systems are fundamental issues that need urgent attention. The production of GO is generally achieved through a top-down route, which includes the usage of concentrated H₂SO₄ along with: 1) concentrated nitric acid and KClO₃ oxidant (Hoffmann); 2) fuming nitric acid and KClO₃ oxidant (Staudenmaier); 3) concentrated phosphoric acid with KMnO₄ (Tour); or 4) sodium nitrate for in-situ production of nitric acid in the presence of KMnO₄ (Hummers). It has been widely assumed that the properties of these four GOs produced by using the above different methods are roughly similar, so the methods have been used interchangeably. However, several studies have reported that the toxicity of graphene-related nanomaterials in biological systems may be influenced by their physiochemical properties, such as surface functional groups and structural defects. In addition, considering how GOs are increasingly used in the field of biomedicine, we are interested to see how the oxygen content/functional groups of GOs can impact their toxicological profiles. Since in-vitro testing is a common first step in assessing the health risks related with engineered nanomaterials, the cytotoxicity of the GOs prepared by the four different oxidative treatments was investigated by measuring the mitochondrial activity in adherent lung epithelial cells (A549) by using commercially available viability assays. The dose-response data was generated by using two assays, the methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay and the water-soluble tetrazolium salt (WST-8). From the viability data, it is evident that there is a strong dose-dependent cytotoxic response resulting from the four GO nanomaterials tested after a 24 h exposure, and it is suggested that there is a correlation between the amounts of oxygen content/functional groups of GOs with their toxicological behavior towards the A549 cells.

Adsorptive remediation of environmental pollutants using novel graphene-based nanomaterials

Pollution of air, water and soil is a worldwide issue for the eco-environment and human society. Removal of various pollutants including inorganic and organic compounds from the environment is a big challenge. Adsorption techniques are usually simple and work effectively. However, the adsorption capacities of materials depend on their porous structure and surface properties. Graphene oxide and graphene are new carbonaceous nanomaterials. Graphene has a large theoretical specific surface area and graphene oxide has functional groups, indicating their potential for the adsorption processes. In the past few years, many investigations have been focused on the applications of graphene or composites in removal of pollutants from air and water. In this paper, we will review recent advances in graphene-related nanomaterials for adsorptive treatment of environmental pollution. Graphene oxide possesses several functional groups and strong acidity, exhibiting high adsorption for basic compounds and cations while graphene shows hydrophobic surface and presents high adsorption to chemicals due to strong π–π interaction. Modification of graphene oxide or graphene with metal oxides or organics can produce various nanocomposites, enhancing adsorption capacity and separation efficiency. Activation of graphene into porous carbonaceous material will be a promising way to further enhance adsorption capacity.

Layer-Dependent Electrical Properties of Graphene-Related Nanomaterials Revealed by Atomic Force Microscopy

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One‐Pot Approach to a Highly Robust Iron Oxide/Reduced Graphene Oxide Nanocatalyst for Fischer–Tropsch Synthesis

Small and stable: Fe2O3 nanoparticles are homogeneously anchored onto reduced graphene oxide through the simultaneous hydrolysis of Fe(acac)3 and reduction of graphene oxide. This nanohybrid is highly resistant to sintering and retains its small particle size upon reduction at 723 K and long-term Fischer–Tropsch synthesis at 543 K (see figure). This work validates the prospect of graphene-related nanomaterials in challenging high-temperature applications.

Graphene-related nanomaterials: tuning properties by functionalization

In this review, we discuss the most recent progress on graphene-related nanomaterials, including doped graphene and derived graphene nanoribbons, graphene oxide, graphane, fluorographene, graphyne, graphdiyne, and porous graphene, from both experimental and theoretical perspectives, and emphasize tuning their stability, electronic and magnetic properties by chemical functionalization.

‘Graphene in Electroanalysis’

Graphene represents a conceptually new class of materials that are only one atom thick. Its unusual properties have already attracted considerable interest of many electrochemists and paved the way for creating new and powerful electrochemical devices. The rapid emergence of graphene has thus opened new horizons for the application of this important nanomaterial in electroanalytical chemistry. Several attractive graphene-based electrode materials, with an attractive electrochemical behavior, have thus been described over the past 3 years. As with all new electrode materials, graphene-related nanomaterials - used for the preparation or modification of new electrodes - require detailed characterization to properly interpret the observed improvements. The present Special Issue of Electroanalysis sheds useful insights into the fundamental electrochemical properties of graphene and reflects the latest advances and current trends in using this exciting form of carbon in electrochemical sensors and biosensors, and in electroanalysis, in general. Given the promising properties of graphene, the studies reported in this Special Issue are just the beginning of a fantastic topic. I would like to thank all the authors who contributed to this issue. Joseph Wang, Editor1

ChemInform Abstract: Graphene‐Based Nanomaterials and Their Electrochemistry

AbstractReview: 38 refs.

Graphene-based nanomaterials and their electrochemistry

Graphene-based nanomaterials are in the forefront of chemical research. This tutorial review provides an introduction to their electrochemistry, its fundamentals and applications. Selected examples of applications in energy storage and sensing are presented. The synthetic methods for preparing graphenes as well as their materials chemistry are thoroughly discussed, as they have a profound influence on the electronic and electrochemical behavior of graphene-related nanomaterials. Inherent electrochemistry and spectroelectrochemistry of graphene nanomaterials is discussed thoroughly. Important application in sensing and energy storage areas are highlighted.