Affinity Of Graphene Oxide Research Articles

Controlled localization of graphene oxide to improve barrier, biodegradation and mechanical properties of PBAT/EVOH

AbstractIncorporating graphene oxide (GO) with controlled localization into poly(butylene adipate‐co‐terephthalate) (PBAT) blends with poly(ethylene vinyl alcohol) (EVOH) aimed to improve barrier properties, biodegradability, and mechanical strength of PBAT. The PBAT/EVOH/GO nanocomposites containing 0 to 1 wt% of GO were prepared by a reactive mixing process in internal mixer. Microscopic images confirmed that the GO nanoplatelets are mainly localized in PBAT phase and then at the interface, contrary to the thermodynamic affinity of GO toward EVOH. The reactive nature of PBAT/EVOH/GO nanocomposites was confirmed via time‐sweep rheological studies where specific changes were observed in melt viscosity over time. The results of microscopic studies, rheometry, tensile test, and dynamic mechanical thermal analysis (DMTA) confirmed that localizing GO at the interface establishes strong interactions between PBAT and EVOH. By the addition of 0.75 wt% GO, tensile and yield strength were improved by 19% and 45%, respectively. Increasing GO significantly increased the hydrolysis degradation rate of the nanocomposites. Furthermore, the addition of GO considerably decreased the oxygen and water vapor permeability of the blends by up to 40% at 1 wt% GO.

Adsorption-solubilization controlled extraction of pyrene from surfactant solutions by graphene oxide

Graphene and its derivatives such as graphene oxide (GO) has attracted increasing attention in water treatment because of its unique physical and chemical properties. Herein, the adsorption performance of GO for a typical polycyclic aromatic hydrocarbon (PAH), pyrene from solutions of either a non-ionic surfactant Tergitol 15-S-7 or an anionic surfactant sodium dodecyl benzene sulphonate (SDBS) is investigated. It demonstrates that the high affinity of GO to pyrene leads to multi-layer adsorption of pyrene, with an adsorption capacity 2 to 3 times of its own weight at a low GO concentration of 3.9 mg/L. Linear two-zone pyrene adsorption isotherms are identified, which should be due to competitive adsorption-solubilization processes of pyrene. Although Tergitol 15-S-7 has a considerably higher solubilization capacity (affinity) for pyrene compared to SDBS, faster adsorption kinetics, larger solid-liquid distribution coefficients, and higher recovery of pyrene from Tergitol 15-S-7 solutions are achieved. The higher affinity of SDBS to GO leads to its competitive adsorption that impairs the adsorption of pyrene by GO. Furthermore, the GO demonstrates excellent adsorption capacity for pyrene even after 5 recycling cycles.

A smart DNAzyme/graphene oxide nanosystem for fluorescent sensing of uranyl ion with high sensitivity and selectivity

Recently, more and more attentions have been paid to the sensitive and selective determination of uranyl ion (UO22+) in environmental water due to its high toxicity and radiotoxicity. The accurate and sensitive determination of UO22+ has been readily performed in the well-equipped laboratories; however, it is still a challenging task for the on-site analysis of UO22+. To address this issue, in the present work, a novel and smart nanosystem based on DNAzyme and graphene oxide (GO) is proposed for the turn-on fluorescent sensing of UO22+ by combining the excellent selectivity of DNAzyme toward UO22+, the super fluorescence quenching ability of GO, and the unique affinity of GO toward DNAs with different structures. The proposed DNAzyme/GO nanosystem displays outstanding analytical performance in terms of wide dynamic response range (0.1–40 nM), low limit of detection (25 pM) and good selectivity over other metal ions. Furthermore, this nanosystem is successfully applied for the UO22+ detection in water samples with satisfactory results, demonstrating its great potential in the environmental monitoring.

Fabrication of Micro-Patterned Chip with Controlled Thickness for High-Throughput Cryogenic Electron Microscopy.

A major limitation for the efficient and high-throughput structure analysis of biomolecules using cryogenic electron microscopy (cryo-EM) is the difficulty of preparing cryo-EM samples with controlled ice thickness at the nanoscale. The silicon (Si)-based chip, which has a regular array of micro-holes with graphene oxide (GO) window patterned on a thickness-controlled silicon nitride (SixNy) film, has been developed by applying microelectromechanical system (MEMS) techniques. UV photolithography, chemical vapor deposition, wet and dry etching of the thin film, and drop-casting of 2D nanosheet materials were used for mass-production of the micro-patterned chips with GO windows. The depth of the micro-holes is regulated to control the ice thickness on-demand, depending on the size of the specimen for cryo-EM analysis. The favorable affinity of GO toward biomolecules concentrates the biomolecules of interest within the micro-hole during cryo-EM sample preparation. The micro-patterned chip with GO windows enables high-throughput cryo-EM imaging of various biological molecules, as well as inorganic nanomaterials.

Role of solution chemistry in the attachment of graphene oxide nanoparticles onto iron oxide minerals with different characteristics.

Given the ubiquity and abundance of the iron oxide minerals and their important roles in affecting the environmental fate of graphene oxide (GO) nanoparticles, the attachment of GO onto three iron oxide minerals (i.e., hematite, goethite, and ferrihydrite) under different solution chemistry conditions was investigated in this study. The main mechanism of the attachment of GO was electrostatic interaction. Calculations based on the DLVO theory showed that the attachment was a favorable process. Interestingly, the affinity of GO towards three iron oxide minerals was in the order of ferrihydrite > goethite > hematite. This result indicates that different characteristics of various iron oxides (e.g., specific surface area, crystal structure, and surface charge, and surface hydroxyl densities) can influence their attachment capacities for GO. The attachment of GO depended on the solution pH and ionic strength. Electrostatic attraction and hydrogen bonding were the important retention mechanisms for GO attachment when pH < pHPZC (the point of zero charge) and pH > pHPZC, respectively. The attachment capacities of iron oxides decreased with increasing ionic strength at lower pH because of the decrease of the electrostatic attraction. Meanwhile, the presence of divalent cations (i.e., Ca2+ and Cu2+) could significantly promote GO attachment mainly by the surface-bridging mechanism. Meanwhile, the enhancement effect of Cu2+ was greater than Ca2+ due to the greater complexation affinity of Cu2+. Furthermore, attachment isotherms showed that the presence of phosphate could inhibit the attachment of GO onto minerals obviously. Because phosphate could form inner-sphere surface complex on the iron oxide surface, and consequently decreased the electrostatic attraction between nanoparticles and minerals. Our study has important implications for predicting the fate of GO in natural environment where amounts of iron oxide minerals are present.

Fractal analysis of pore structures in graphene oxide-carbon nanotube based cementitious pastes under different ultrasonication

Abstract Nano cement additive using a hybrid of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) combines the excellent affinity of GO and the superior mechanical properties of MWCNTs. Ultrasonication is the key process to disperse the GO/MWCNTs and further optimizes the pore structures of cement-based pastes. Fractal dimension can effectively and quantitatively characterize the pore structures of cementitious composites. The present study investigates the fractal dimensions of pore structures of GO/MWCNT-OPC pastes under power- and time-controlled ultrasonication based on the mercury intrusion porosimetry (MIP) tests data. The finding of this study shows that comparing to calculating the fractal dimension of the overall pore size range, assessing the variations of fractal dimension of individual pore size range is more effective in evaluating the pore characteristic. The fractal dimension of larger capillary pores $$\left( {{D}_{&gt;{{10}^{4}}nm}} \right)$$can be use to describe the change of pore structure of GO/MWCNT-OPC pastes under ultrasonication treatment with sufficient accuracy as higher value of $${{D}_{&gt;{{10}^{4}}nm}}$$indicates better pore characteristics. The fractal dimension change trend of mesopores is always opposite to that of bigger capillary pores. Modest increment in both power- and time-controlled ultrasonication seems to result in the increase of the fractal dimension of capillary pores and lead to better reinforcement effects. Prolongation of ultrasonication time slightly influences the pore structure of the specimens, while nano cement additives exposed to excess ultrasonication power fail to afford adequate reinforcing effect and finally cause the deterioration of the pore structures. The findings of this study can provide helpful information of GO/MWCNT-OPC pastes and ultrasonication treatment in the future.

Influence of ultrasonication on the dispersion and enhancing effect of graphene oxide–carbon nanotube hybrid nanoreinforcement in cementitious composite

Nano-engineering cement binder using a hybrid of carbon nanotubes (CNTs) and graphene oxide (GO) combines the superior mechanical properties of CNTs and the good dispersibility and affinity of GO. Ultrasonication is a key process implemented in the dispersion of CNTs and GO. The present study characterizes the effect of ultrasonication on the dispersion and size of the GO/CNT particles by using an ultraviolet spectrophotometer and Zetasizer μV detector, respectively. The mechanical properties of GO/CNT-OPC pastes treated with different ultrasonication time and power levels were tested and their microstructure was investigated using scanning electron microscopy and mercury intrusion porosimetry. The results of this study not only reveal that differences in ultrasonication can cause the mechanical properties of the GO/CNT-OPC composite to vary by −11.7–78.8% but also show that the effect of the amount of ultrasonication energy can vary significantly when different ultrasonication time or power levels are adopted. The porosity of the composite is found to have a nonlinear correlation with the ultrasonication. The findings of this study can promote understanding of GO/CNT-OPC composites and help to guide the implementation of ultrasonication in the future.

Graphene oxide-facilitated transport of Pb2+ and Cd2+ in saturated porous media

This paper provides an overview of the effect of graphene oxide (GO) on sorption, transport, and remobilization of Pb2+ and Cd2+ ions in saturated porous media. The affinity of GO to Pb2+ and Cd2+ ions was investigated via kinetic and isothermal sorption experiments. Laboratory packed-column experiments were also conducted to investigate the cotransport of Pb2+ and Cd2+ ions with GO across a quartz sand matrix. In addition, the Pb2+- and Cd2+-preequilibrated sand column was sequentially flushed with GO to test its remobilization effect on these ions. GO exhibited a high affinity toward both Pb2+ and Cd2+ ions with maximum sorption capacities of 1428.57 and 911.43mgg−1, respectively. On the other hand, while GO improved the transport ability of Pb2+ and Cd2+, both ions reduced the mobility of GO in saturated porous media. Data from the elution experiment revealed that the high affinity of GO toward the metal ions led to the remobilization of the presorbed Pb2+ and Cd2+ ions onto the quartz sand surfaces and their concurrent migration across the sand column. XDLVO (Extended Derjaguin-Landau-Verwey-Overbeek) calculations were employed to interpret the GO transport behavior in the column wells. The cotransport of Pb2+ and Cd2+ ions with GO in the saturated quartz sand was successfully simulated by the advection-dispersion-reaction equation. Findings from this study provide an insight on the potential implications of remobilization and spread of pollutants by nanomaterials existing in vulnerable ecosystems.

Pervaporation of toluene and iso‐octane through poly(vinyl alcohol)/graphene oxide nanoplate mixed matrix membranes: Comparison of crosslinked and noncrosslinked membranes

ABSTRACTRemoval of aromatic compounds from fuel is an essential requirement in new environmental policies. In the present study, poly(vinyl alcohol)/graphene oxide (GO) mixed matrix membranes were prepared and applied to the separation of toluene from iso‐octane by pervaporation, considering the similarity and interaction between graphene and aromatics. The effects of crosslinking and GO content on separation efficiency have been investigated in detail. Owing to the high affinity of GO with toluene through s and π bonds, the selectivity of the membranes was increased by incorporating a low amount of GO. The results also indicated that noncrosslinked membranes have higher selectivity and permeation flux due to higher crystallinity and also have lower mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45853.

PH-Responsive Graphene Oxide-DNA Nanosystem for Live Cell Imaging and Detection.

The interaction between graphene oxide (GO) and DNA is very sensitive to the environment. For example, under acidic conditions, the affinity of GO for DNA is enhanced, weakening the capability of GO to distinguish DNAs with different conformations. This effect has impeded the development of sensitive pH biosensors based on GO-DNA nanosystems. In this work, we systematically studied the affinity between GO and i-motif forming oligonucleotides (IFOs) at different pH values and developed a herring sperm DNA (HSD) treatment method. Using this method, HSD occupies the surface of GO, compromising the attractive force of GO that is significantly enhanced under acidic conditions. As a result, the ability of GO to distinguish between "open" and "closed" IFOs is successfully generalized to a wider pH range. Finally, a pH-sensitive GO-IFO nanosystem was fabricated that showed excellent sensing ability both in vitro and for intracellular pH detection. Because the interaction between GO and DNA is the basis for constructing GO-DNA biosensors, the strategy developed in this work shows great potential to be applied in a variety of other GO-DNA sensing systems.

A real time S1 assay at neutral pH based on graphene oxide quenched fluorescence probe

As the extracellular nuclease of Aspergillus, S1 nuclease can split single and double-stranded DNA into oligo- or mononucleotides, while preferentially digests single-stranded nucleic acids. Furthermore, the existence of S1 can be the standard to identify Aspergillus and used to evaluate the severity of Aspergillosis. Herein, a simple and sensitive fluorescent sensing platform for S1 assay was developed based on the S1-induced DNA strand scission and the difference in affinity of graphene oxide (GO) for single-stranded DNA containing different bases. This platform was applied to monitor S1 activity and study the kinetics in real time. Results indicated that the detection limit is 0.5U/mL. The Km and kcat at 45°C, are 1.4±0.12μM and 0.6min−1, respectively. Moreover, by monitoring the effect of chemical drugs on S1 activity, we found that 2mM of erythromycin, sodium penicillin, carbenicillin disodium and ampicillin can inhibit S1 activity about 8%, 60%, 61% and 66%, respectively, while gentamycin sulfate is a stimulator. Overall, the assay platform based on graphene oxide quenched fluorescence probe is successfully constructed to study the enzymatic activity of S1 and used for screening antibiotics.

The preparation and characterization of polycaprolactone/graphene oxide biocomposite nanofiber scaffolds and their application for directing cell behaviors

Biocomposite nanofiber scaffolds of polycaprolactone (PCL) with different graphene oxide (GO) concentrations were prepared using electrospinning technology. The successful incorporation of GO nanosheets into PCL polymer nanofibers improved the thermal and mechanical properties of the nanofibers because of the intrinsic properties developed due to the interactions of GO and PCL. In order to estimate the biocompatibility of PCL/GO composite scaffolds, mouse marrow mesenchymal stem cells (mMSCs) and low-differentiated rat pheochromocytoma (PC12-L) cells were cultured. Initial adhesion and spreading of the mMSCs and PC12-L cells on PCL/GO composite scaffolds with moderate addition of GO (0.3 and 0.5 wt%) were significantly superior to those on pure PCL scaffolds, and the cells exhibited typical fibroblast- and neuron-like morphologies with obvious pseudopods and mature appearance, respectively. A small amount of GO did not restrain the proliferation and viability of the mMSCs and PC12-L cells, which indicated appreciable cell affinity of GO. Moreover, the hybridization of GO nanosheets and PCL polymer dramatically enhanced the differentiation of the mMSCs and PC12-L cells into osteo- and neuro-like cells, respectively. All these results suggest that PCL/GO composite nanofibers could be a promising alternative material as biocompatible scaffolds for tissue engineering.

High performance system for protein assays: synergistic effect of terminal protection strategy and graphene oxide platform

A straightforward biosensor for protein assay has been developed based on terminal protection of small molecule-linked DNA by target protein and the difference in affinity of graphene oxide for ssDNA containing different numbers of bases in length.

Detection of UV-induced mutagenic thymine dimer using graphene oxide.

In this paper, we report for the first time that graphene oxide (GO) can interact with mutagenic DNA but not intact DNA. After UV-irradiated fluorophore-linked DNA containing thymine repeats was mixed with GO, a decrease in fluorescence was observed in a time-dependent manner. In contrast, no fluorescence change was observed with intact DNA, indicating that UV irradiation of DNA resulted in the formation of mutagenic bases. Because GO is known to act as a fluorescence quencher, the decreased fluorescence implies adsorption of the UV-irradiated DNA onto GO. It appears that the decreased fluorescence might result from the greater accessibility of hydrophobic methyl groups and phenyl rings of thymine dimers to GO and from deformed DNA structures with less effective charge shielding under salt-containing conditions. Using this affinity of GO for mutagenic DNA, we could detect UV-irradiated DNA at concentrations as low as 100 pM. We were also able to analyze the ability of phototoxic drugs to catalyze the formation of mutagens under UV irradiation with GO. Because our method is highly sensitive and feasible and does not require the pretreatment of DNA, we propose that it could accelerate the screening of potential phototoxic drug candidates that would be able to sensitize mutagenic dsDNA.

A label-free fluorescent probe for Hg²⁺ and biothiols based on graphene oxide and Ru-complex.

A novel, selective and sensitive switch-on fluorescent sensor for Hg2+ and switch-off fluorescent probe for biothiols was developed by using [Ru(bpy)2(pip)]2+ as the signal reporter and graphene oxide (GO) as the quencher. Due to the affinity of GO towards single-stranded DNA (ss-DNA) and [Ru(bpy)2(pip)]2+, the three components assembled, resulting in fluorescence quenching. Upon addition of Hg2+, a double-stranded DNA (ds-DNA) via T–Hg2+–T base pairs was formed, and [Ru(bpy)2(pip)]2+ intercalated into the newly formed ds-DNA. Then, [Ru(bpy)2(pip)]2+ and ds-DNA were removed from the surface of GO, resulting in the restoration of fluorescence. Subsequently, upon addition of biothiols, Hg2+ was released from ds-DNA, due to the higher affinity of Hg2+ to the sulfur atoms of biothiols, which could induce ds-DNA unwinding to form ss-DNA. Then ss-DNA and [Ru(bpy)2(pip)]2+ were adsorbed on the surface of GO, the fluorescence of [Ru(bpy)2(pip)]2+ was quenched again. Therefore, the changes in emission intensity of [Ru(bpy)2(pip)]2+ directly correlated to the amount of detection target (Hg2+ or biothiols) in solution. The assay exhibited high sensitivity and selectivity, with the limits of detection for Hg2+, cysteine (Cys) and glutathione (GSH) to be 2.34 nM, 6.20 nM and 4.60 nM, respectively.

Graphene oxide and metal-mediated base pairs based "molecular beacon" integrating with exonuclease I for fluorescence turn-on detection of biothiols.

A novel fluorescence turn-on strategy, based on the resistance of metal-mediated molecular-beacons (MBs) toward nuclease digestion and the remarkable difference in the affinity of graphene oxide (GO) with MBs and the mononucleotides, is designed for the biothiols assay. Specifically, the metal-mediated base pairs facilitate the dye labeled MBs to fold into a hairpin structure preventing the digestion by exonuclease I, and thus allow the fluorescence quenching. The competition binding by biothiols removes metal ions from the base pairs, causing the nuclease reaction, and less decrease in the fluorescence is obtained after incubating with GO due to the weak affinity of the product-mononucleotides to GO. Hg(2+)-mediated MBs were firstly designed for the biothiols detection, and glutathione (GSH) was applied as the model target. Under the optimal conditions, the approach exhibits high sensitivity to GSH with a detection limit of 1.53 nM. Ag(+)-mediated MBs based sensor was also constructed to demonstrate its versatility, and cysteine was studied as the model target. The satisfactory results in the determination of biothiols in serum demonstrate that the method possesses great potential for detecting thiols in biological fluids. This new approach is expected to promote the exploitation of metal-mediated base pairs-based biosensors in biochemical and biomedical studies.

A duplex–triplex nucleic acid nanomachine that probes pH changes inside living cells during apoptosis

A duplex-triplex switchable DNA nanomachine was fabricated and has been applied for the demonstration of intracellular acidification and apoptosis of Ramos cells, with graphene oxide (GO) not only as transporter but also as fluorescence quencher. The machine constructed with triplex-forming oligonucleotide exhibited duplex-triplex transition at different pH conditions. By virtue of the remarkable difference in affinity of GO with single-stranded DNA and triplex DNA, and the super fluorescence quenching efficiency of GO, the nanomachine functions as a pH sensor based on fluorescence resonance energy transfer. Moreover, taking advantage of the excellent transporter property of GO, the duplex-triplex/GO nanomachine was used to sense pH changes inside Ramos cells during apoptosis. Fluorescence images showed different results between living and apoptotic cells, illustrating the potential of DNA scaffolds responsive to more complex pH triggers in living systems.

An ultra-high sensitive platform for fluorescence detection of micrococcal nuclease based on grapheneoxide

Micrococcal nuclease (MNase) is the extracellular nuclease of Staphylococcus aureus (S. aureus). It preferentially digests single-stranded nucleic acids. The existence of MNase can be the standard to identify S. aureus and the content of MNase can be used to evaluate the pathogenicity of S. aureus. Herein, an ultra-high sensitive and selective fluorescent sensing platform for MNase is developed based on MNase-induced DNA strand scission and the difference in affinity of graphene oxide (GO) for single-stranded DNA containing different numbers of bases in length. In the absence of MNase, the adsorption of the dye-labeled ssDNA on GO makes the dyes close proximity to GO surface resulting in high efficiency quenching of fluorescence of the dyes. Conversely, and very importantly, in the presence of MNase, it cleaves the dye-labeled ssDNA into small fragments. The introduction of GO into the sensing solution results in weak quenching of the fluorescence of the dyes due to the weak affinity of the short dye-labeled oligonuleotide fragment to GO, and the fluorescence intensity gradually increases with increasing concentration of MNase. MNase can be detected in a range of 8×10−5 to 1.6×10−3unit/mL with a detection limit of 2.7×10−5unit/mL and good selectivity. The detection limit is of two orders of magnitude lower than those reported fluorescence MNase assays. Moreover, when the GO-based biosensor is used in S. aureus sample assays, preeminent fluorescence signals are obtained, thus the platform of the GO-based biosensor can be used to detect MNase in real-world samples.

A graphene-based real-time fluorescent assay of deoxyribonuclease I activity and inhibition

Using the remarkable difference in the affinity of graphene oxide (GO) with double strand DNA (dsDNA) and short DNA fragments, we report for the first time a GO-based nonrestriction nuclease responsive system. Our system was composed of GO and a fluorescent dye fluorescein amidite (FAM)-labeled dsDNA substrate (F-dsDNA). At first, the fluorescence of this F-dsDNA substrate was quenched upon addition of GO. When nuclease was added to the mixture of dsDNA and GO, hydrolysis of dsDNA was initiated and small DNA fragments were produced. As a result, the short FAM-linked DNA fragments were released from GO due to the weak affinity of GO with short DNA fragments, and the fluorescence got a restoration. At present, many sensing systems are based on the fact that GO prefers to bind long single strand DNA (ssDNA) over dsDNA or short ssDNA. As for our system, GO has a prior binding with dsDNA over short DNA fragments. Compared with previous methods, this assay platform has some advantages. First, since GO can be prepared in large quantities from graphite available at very low cost, this method shows advantages of simplicity and cost efficiency. Besides, the proposed GO-based nuclease assay provides high sensitivity due to the super quenching capacity of GO. Using deoxyribonuclease I (DNase I) as a model system, DNase I activity can be quantitatively analyzed by the velocity of the enzymatic reaction, and 1.75UmL−1 DNase I can be significantly detected. Moreover, the fluorescent intensity with various concentrations of nuclease becomes highly discriminating after 3–8min. Thus, it is possible to detect nuclease activity within 3–8min, which demonstrates another advantage of quick response of the present system. Finally, use of dsDNA as substrate, our method can achieve real-time nuclease activity/inhibition assay, which is time-saving and effortless.

An S1 Nuclease Mapping Method for Detection of Low Abundance Transcripts

As the extracellular nuclease of Aspergillus, S1 nuclease can split single and double-stranded DNA into oligo- or mononucleotides, while preferentially digests single-stranded nucleic acids. Furthermore, the existence of S1 can be the standard to identify Aspergillus and used to evaluate the severity of Aspergillosis. Herein, a simple and sensitive fluorescent sensing platform for S1 assay was developed based on the S1-induced DNA strand scission and the difference in affinity of graphene oxide (GO) for single-stranded DNA containing different bases. This platform was applied to monitor S1 activity and study the kinetics in real time. Results indicated that the detection limit is 0.5 U/mL. The Km and kcat at 45 °C, are 1.4 ± 0.12 μM and 0.6 min− 1, respectively. Moreover, by monitoring the effect of chemical drugs on S1 activity, we found that 2 mM of erythromycin, sodium penicillin, carbenicillin disodium and ampicillin can inhibit S1 activity about 8%, 60%, 61% and 66%, respectively, while gentamycin sulfate is a stimulator. Overall, the assay platform based on graphene oxide quenched fluorescence probe is successfully constructed to study the enzymatic activity of S1 and used for screening antibiotics.