Functionalized graphene oxide in enzyme engineering: a selective modulator for enzyme activity and thermostability

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

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

FROM THE CLINICAL EDITOR

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

Programmable Downregulation of Enzyme Activity Using a Fever and NIR-Responsive Molecularly Imprinted Nanocomposite

A fever and NIR-responsive molecularly imprinted nanocomposite is designed for programmable downregulation of enzyme activity. The target enzyme can be captured specifically and its activity can be downregulated only when body temperature increases abnormally. Upon NIR irradiation, the temperature of the destination region can increase accordingly inducing a further decrease in the enzyme activity.

Graphene oxide as a protein matrix: influence on protein biophysical properties

Background

This study provides fundamental information on the influence of graphene oxide (GO) nanosheets and glycans on protein catalytic activity, dynamics, and thermal stability. We provide evidence of protein stabilization by glycans and how this strategy could be implemented when GO nanosheets is used as protein immobilization matrix. A series of bioconjugates was constructed using two different strategies: adsorbing or covalently attaching native and glycosylated bilirubin oxidase (BOD) to GO.

Results

Bioconjugate formation was followed by FT-IR, zeta-potential, and X-ray photoelectron spectroscopy measurements. Enzyme kinetic parameters (k_m and k_cat) revealed that the substrate binding affinity was not affected by glycosylation and immobilization on GO, but the rate of enzyme catalysis was reduced. Structural analysis by circular dichroism showed that glycosylation did not affect the tertiary or the secondary structure of BOD. However, GO produced slight changes in the secondary structure. To shed light into the biophysical consequence of protein glycosylation and protein immobilization on GO nanosheets, we studied structural protein dynamical changes by FT-IR H/D exchange and thermal inactivation.

Conclusions

It was found that glycosylation caused a reduction in structural dynamics that resulted in an increase in thermostability and a decrease in the catalytic activity for both, glycoconjugate and immobilized enzyme. These results establish the usefulness of chemical glycosylation to modulate protein structural dynamics and stability to develop a more stable GO-protein matrix.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-015-0134-0) contains supplementary material, which is available to authorized users.

Graphene Oxide Selectively Enhances Thermostability of Trypsin

In the past few years, graphene and its derivative, graphene oxide (GO), have been extensively studied for their applications in biotechnology. In our previous work, we reported certain PEGylated GOs (GO-PEGs) can selectively promote trypsin activity and enhance its thermostability. To further explore this, here we synthesized a series of GO-PEGs with varying PEGylation degrees. Enzymatic activity assay shows that both GO and GO-PEGs can protect trypsin, but not chymotrypsin, from thermal denaturation at high temperature. Surprisingly, the lower the PEGylation degree, the better the protection, and GO as well as the GO-PEG with the lowest PEGylation degree show the highest protection efficiency (∼70% retained activity at 70 °C). Fluorescence spectroscopy analysis shows that GO/GO-PEGs have strong interactions with trypsin. Molecular Dynamics (MD) simulation results reveal that trypsin is adsorbed onto the surface of GO through its cationic residues and hydrophilic residues. Different from chymotrypsin adsorbed on GO, the active site of trypsin is covered by GO. MD simulation at high temperature shows that, through such interaction with GO, trypsin's active site is therefore stabilized and protected by GO. Our work not only illustrates the promising potential of GO/GO-PEGs as efficient, selective modulators for trypsin, but also provides the interaction mechanism of GO with specific proteins at the nano-bio interface.

Increasing the activity of immobilized enzymes with nanoparticle conjugation

The efficiency and selectivity of enzymatic catalysis is useful to a plethora of industrial and manufacturing processes. Many of these processes require the immobilization of enzymes onto surfaces, which has traditionally reduced enzyme activity. However, recent research has shown that the integration of nanoparticles into enzyme carrier schemes has maintained or even enhanced immobilized enzyme performance. The nanoparticle size and surface chemistry as well as the orientation and density of immobilized enzymes all contribute to the enhanced performance of enzyme-nanoparticle conjugates. These improvements are noted in specific nanoparticles including those comprising carbon (e.g., graphene and carbon nanotubes), metal/metal oxides and polymeric nanomaterials, as well as semiconductor nanocrystals or quantum dots.

Inhibiting the VIM-2 Metallo-β-Lactamase by Graphene Oxide and Carbon Nanotubes

Metallo-β-lactamases (MBLs) degrade a broad spectrum of antibiotics including the latest carbapenems. So far, limited success has been achieved in developing its inhibitors using small organic molecules. VIM-2 is one of the most studied and important MBLs. In this work, we screened 10 nanomaterials, covering a diverse range of surface properties including charge, hydrophobicity, and specific chemical bonding. Among these, graphene oxide and carbon nanotubes are the most potent inhibitors, while most other materials do not show much inhibition effect. The inhibition is noncompetitive and is attributed to the hydrophobic interaction with the enzyme. Adsorption of VIM-2 was further probed using protein displacement assays where it cannot displace or be displaced by bovine serum albumin (BSA). This information is useful for rational design inhibitors for MBLs and more specific inhibition might be achieved by further surface modifications on these nanocarbons.

Biological relevance of oxidative debris present in as-prepared graphene oxide

The influence of oxidative debris (OD) present in as-prepared graphene oxide (GO) suspensions on proteins and its toxicity to human embryonic kidney cells (HEK-293T) are reported here. The OD was removed by repeated washing with aqueous ammonia to produce the corresponding base-washed GO (bwGO). The loading (w/w) of bovine serum albumin (BSA) was increased by 85% after base washing, whereas the loading of hemoglobin (Hb) and lysozyme (Lyz), respectively, was decreased by 160% and 100%. The secondary structures of 13 different proteins bound to bwGO were compared with the corresponding proteins bound to GO using the UV circular dichroism spectroscopy. There was a consistent loss of protein secondary structure with bwGO when compared with proteins bound to GO, but no correlation between either the isoelectric point or hydrophobicity of the protein and the extent of structure loss was observed. All enzymes bound to bwGO and GO indicated significant activities, and a strong correlation between the enzymatic activity and the extent of structure retention was noted, regardless of the presence or absence of OD. At low loadings (<100 μg/mL) both GO and bwGO showed excellent cell viability but substantial cytotoxicity (~40% cell death) was observed at high loadings (>100 μg/mL). In control studies, OD by itself did not alter the growth rate even after a 48-h incubation. Thus, the presence of OD in GO played a very important role in controlling the chemical and biological nature of the protein-GO interface and the presence of OD in GO improved its biological compatibility when compared to bwGO.

A new sample preparation method for the absolute quantitation of a target proteome using 18O labeling combined with multiple reaction monitoring mass spectrometry

A new sample preparation method for target proteome absolute quantitation using ¹⁸O labeling-MRM MS.

Mechanism of DNA adsorption and desorption on graphene oxide

Graphene oxide (GO) adsorbing a fluorophore-labeled single-stranded (ss) DNA serves as a sensor system because subsequent desorption of the adsorbed probe DNA from GO in the presence of complementary target DNA enhances the fluorescence. In this study, we investigated the interaction of single- and double-stranded (ds) DNAs with GO by using a fluorescently labeled DNA probe. Although GO is known to preferentially interact with ssDNA, we found that dsDNA can also be adsorbed on GO, albeit with lower affinity. Furthermore, the status of ssDNA or dsDNA previously adsorbed on the GO surface was investigated by adding complementary or noncomplementary DNA (cDNA or non-cDNA) to the adsorption complex. We observed that hybridization occurred between the cDNA and the probe DNA on the GO surface. On the basis of the kinetics driven by the incoming additional DNA, we propose a mechanism for the desorption of the preadsorbed probe DNA from the GO surface: the desorption of the GO-adsorbed DNA was facilitated following its hybridization with cDNA on the GO surface; when the GO surface was almost saturated with the adsorbed DNA, nonspecific desorption dominated the process through a simple displacement of the GO-adsorbed DNA molecules by the incoming DNA molecules because of the law of mass action. Our results can be applied to design appropriate DNA probes and to choose proper GO concentrations for experimental setups to improve specific signaling in many biosensor systems based on the GO platform.

Versatile matrix for constructing enzyme-based biosensors

A versatile matrix was fabricated and utilized as a universal interface for the construction of enzyme-based biosensors. This matrix was formed on the gold electrode via combining self-assembled monolayer of 2,3-dimercaptosuccinic acid with gold nanoparticles. Gold nanoparticles were electrochemically deposited. Electrochemistry of three redox enzymes (catalase, glucose oxidase, and horseradish peroxidase) was investigated on such a matrix. The electrocatalytic monitoring of hydrogen peroxide and glucose was conducted on this matrix after being coated with those enzymes. On them the monitoring of hydrogen peroxide and glucose shows rapid response times, wide linear working ranges, low detection limits, and high enzymatic affinities. This matrix is thus a versatile and suitable platform to develop highly sensitive enzyme-based biosensors.

The selective interaction between silica nanoparticles and enzymes from molecular dynamics simulations

Nanoscale particles have become promising materials in many fields, such as cancer therapeutics, diagnosis, imaging, drug delivery, catalysis, as well as biosensors. In order to stimulate and facilitate these applications, there is an urgent need for the understanding of the interaction mode between the nano-particles and proteins. In this study, we investigate the orientation and adsorption between several enzymes (cytochrome c, RNase A, lysozyme) and 4 nm/11 nm silica nanoparticles (SNPs) by using molecular dynamics (MD) simulation. Our results show that three enzymes are adsorbed onto the surfaces of both 4 nm and 11 nm SNPs during our MD simulations and the small SNPs induce greater structural stabilization. The active site of cytochrome c is far away from the surface of 4 nm SNPs, while it is adsorbed onto the surface of 11 nm SNPs. We also explore the influences of different groups (-OH, -COOH, -NH2 and CH3) coated onto silica nanoparticles, which show significantly different impacts. Our molecular dynamics results indicate the selective interaction between silicon nanoparticles and enzymes, which is consistent with experimental results. Our study provides useful guides for designing/modifying nanomaterials to interact with proteins for their bio-applications.

Chiral functionalization of graphene oxide by optically active helical-substituted polyacetylene chains and its application in enantioselective crystallization

This article reports an original, versatile strategy to chirally functionalize graphene oxide (GO) with optically active helical-substituted polyacetylene. GO was first converted into alkynyl-GO containing polymerizable -C≡C moieties, which took part in the polymerization of another chiral acetylenic monomer, yielding the expected GO hybrid covalently grafted with chiral helical polyacetylene chains. Transmission electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyses verified the successful attachment of substituted polyacetylene chains on GO by covalent chemical bonding. Moreover, circular dichroism effects and UV-vis absorption demonstrated that the GO hybrid possessed fascinating optical activity. It also largely improved the dispersibility of GO in tetrahydrofuran. The GO-derived hybrid was further used as a chiral inducer toward enantioselective crystallization of alanine enantiomers. l-Alanine was preferably induced to crystallize, forming rodlike crystals.

Biofunctionalization of α-zirconium phosphate nanosheets: toward rational control of enzyme loading, affinities, activities and structure retention

Controlling the properties of enzymes bound to solid surfaces in a rational manner is a grand challenge. Here we show that preadsorption of cationized bovine serum albumin (cBSA) to α-Zr(IV) phosphate (α-ZrP) nanosheets promotes enzyme binding in a predictable manner, and surprisingly, the enzyme binding is linearly proportional to the number of residues present in the enzyme or its volume, providing a powerful, new predictable tool. The cBSA loaded α-ZrP (denoted as bZrP) was tested for the binding of pepsin, glucose oxidase (GOX), tyrosinase, catalase, myoglobin and laccase where the number of residues increased from the lowest value of ∼153 to the highest value of 2024. Loading depended linearly on the number of residues, rather than enzyme charge or its isoelectric point. No such correlation was seen for the binding of these enzymes to α-ZrP nanosheets without the preadsorption of cBSA, under similar conditions of pH and buffer. Enzyme binding to bZrP was supported by centrifugation studies, powder X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy. All the bound enzymes retained their secondary structure and the extent of structure retention depended directly on the amount of cBSA preadsorbed on α-ZrP, prior to enzyme loading. Except for tyrosinase, all enzyme/bZrP biocatalysts retained their enzymatic activities nearly 90-100%, and biofunctionalization enhanced the loading, improved structure retention and supported higher enzymatic activities. This approach of using a chemically modified protein to serve as a glue, with a predictable affinity/loading of the enzymes, could be useful to rationally control enzyme binding for applications in advanced biocatalysis and biomedical applications.

Mechanism of graphene oxide as an enzyme inhibitor from molecular dynamics simulations

Graphene and its water-soluble derivative, graphene oxide (GO), have attracted huge attention because of their interesting physical and chemical properties, and they have shown wide applications in various fields including biotechnology and biomedicine. Recently, GO has been shown to be the most efficient inhibitor for α-chymotrypsin (ChT) compared with all other artificial inhibitors. However, how GO interacts with bioactive proteins and its potential in enzyme engineering have been rarely explored. In this study, we investigate the interactions between ChT and graphene/GO by using molecular dynamics (MD) simulation. We find that ChT is adsorbed onto the surface of GO or graphene during 100 ns MD simulations. The α-helix of ChT plays as an important anchor to interact with GO. The cationic and hydrophobic residues of ChT form strong interactions with GO, which leads to the deformation of the active site of ChT and the inhibition of ChT. In comparison, the active site of ChT is only slightly affected after ChT adsorbed onto the graphene surface. In addition, the secondary structure of ChT is not affected after it is adsorbed onto GO or graphene surface. Our results illustrate the mechanism of the interaction between GO/graphene and enzyme and provide guidelines for designing efficient artificial inhibitors.

Graphene-based nanobiocatalytic systems: recent advances and future prospects

Graphene-based nanomaterials are particularly useful nanostructured materials that show great promise in biotechnology and biomedicine. Owing to their unique structural features, exceptional chemical, electrical, and mechanical properties, and their ability to affect the microenvironment of biomolecules, graphene-based nanomaterials are suitable for use in various applications, such as immobilization of enzymes. We present the current advances in research on graphene-based nanomaterials used as novel scaffolds to build robust nanobiocatalytic systems. Their catalytic behavior is affected by the nature of enzyme-nanomaterial interactions and, thus, the availability of methods to couple enzymes with nanomaterials is an important issue. We discuss the implications of such interactions along with future prospects and possible challenges in this rapidly developing area.

Enzyme hyperactivation system based on a complementary charged pair of polyelectrolytes and substrates

Artificial enzyme activators are of great interest for enzyme applications in a wide range of research fields. Here, we report an enzyme hyperactivation system using polyelectrolytes that are complementary to charged substrates. The enzyme activity of α-chymotrypsin (ChT) for a cationic substrate increased 7-fold at pH 7.0 in the presence of anionic poly(acrylic acid) (PAAc) and for an anionic substrate increased 18-fold at pH 7.0 in the presence of cationic poly(allylamine) (PAA). Analysis of salt and pH effects, enzyme kinetics, dynamic light scattering (DLS), and circular dichroism (CD) indicated that the enzyme activation results from favorable electrostatic interactions between oppositely charged substrates and polyelectrolytes surrounding the enzymes. This hyperactivation system does not require laborious mutagenesis or chemical modification of enzymes and thus is relevant to a number of applications.

A capillary electrophoresis-based immobilized enzyme reactor using graphene oxide as a support via layer by layer electrostatic assembly

Using graphene oxide as an enzyme support, we developed a novel CE-based microreactor via layer-by-layer electrostatic assembly, which can be used for accurate on-line analysis and characterization of peptides and proteins.

Tuning the activities and structures of enzymes bound to graphene oxide with a protein glue

Graphene oxide (GO) is being investigated extensively for enzyme and protein binding, but many enzymes bound to GO denature considerably and lose most of their activities. A simple, novel, and efficient approach is described here for improving the structures and activities of enzymes bound to GO such that bound enzymes are nearly as active as those of the corresponding unbound enzymes. Our strategy is to preadsorb highly cationized bovine serum albumin (cBSA) to passivate GO, and cBSA/GO (bGO) served as an excellent platform for enzyme binding. The binding of met-hemoglobin, glucose oxidase, horseradish peroxidase, BSA, catalase, lysozyme, and cytochrome c indicated improved binding, structure retention, and activities. Nearly 100% of native-like structures of all the seven proteins/enzymes were noted at near monolayer formation of cBSA on GO (400% w/w), and all bound enzymes indicated 100% retention of their activities. A facile, benign, simple, and general method has been developed for the biofunctionalization of GO, and this approach of coating with suitable protein glues expands the utility of GO as an advanced biophilic nanomaterial for applications in catalysis, sensing, and biomedicine.

Density functional theory study on the interactions of L-cysteine with graphene: adsorption stability and magnetism

Understanding the interactions between graphene and biomolecules is of fundamental relevance to the area of nanobiotechnology. Herein, we take l-cysteine as the probe biomolecule and investigate its adsorption on pristine graphene and B-, N-, Al-, Ni-, Ga-, Pd-doped graphene using density functional theory calculations. Three kinds of upright adsorption configurations, via unprotonated functional groups (-SH, -NH2, -COOH), are considered. The calculations reveal pristine graphene physically adsorbs l-cysteine. N-doped graphene shows physisorption towards the S-end and N-end l-cysteine, and chemisorption towards the O-end radical. Strong chemisorption, with site-specific preference, occurs on Al-, Ni-, Ga- and Pd-doped graphene, accompanied by severe structural changes. Spin polarization with an unusual mirror symmetry on Ni- and Pd-doped graphene is induced by chemisorption of unprotonated l-cysteine, except for O-end adsorption on Pd-doped graphene. The magnetization arises mainly from spin polarization of the C 2pz orbital, with a minor magnetism located on Ni or Pd. The influence of van der Waals forces is also evaluated. A thorough analysis of the adsorption stability and magnetism of these systems would be beneficial to facilitate applications in graphene-based biosensing, biomolecule immobilization, magnetic bio-separation and other fields in bionanotechnology.

Rationally designed nucleobase and nucleotide coordinated nanoparticles for selective DNA adsorption and detection

Nanomaterials for DNA adsorption are useful for sequence-specific DNA detection. Current materials for DNA adsorption employ electrostatic attraction, hydrophobic interaction, or π-π stacking, none of which can achieve sequence specificity. Specificity might be improved by involving hydrogen bonding and metal coordination. In this work, a diverse range of nucleobase/nucleotide (adenine, adenosine, adenosine 5'-triphosphate (ATP), adenosine 5'-monophosphate (AMP), and guanosine 5'-triphosphate (GTP)) coordinated materials containing various metal ions (Au(III), Ag(I), Ce(III), Gd(III), and Tb(III)) are prepared. In most cases, nanoparticles are formed. These materials have different surface charges, and positively charged particles only show nonspecific DNA adsorption. Negatively charged materials give different adsorption kinetics for different DNA sequences, where complementary DNA homopolymers are adsorbed faster than other sequences. Therefore, the bases in the coordinated materials can still form base pairs with the DNA. The adsorption strength is mainly controlled by the metal ions, where Au shows the strongest adsorption while lanthanides are weaker. These materials can be used as sensors for DNA detection and can also deliver DNA into cells with no detectable toxicity. By tuning the nanoparticle formulation, enhanced detection can be achieved. This study is an important step toward rational design of materials to achieve specific interactions between biomolecules and synthetic nanoparticle surfaces.

A graphene oxide-based platform for the assay of RNA synthesis by RNA polymerase using a fluorescent peptide nucleic acid probe

We report a simple, direct fluorometric assay based on graphene oxide (GO) for RNA polymerase-mediated RNA synthesis. In principle, fluorescent peptide nucleic acid (PNA) probes were designed, and annealed with RNA products and the resultant RNA-PNA hybrids induced the recovery of fluorescence intensity of the PNA probes adsorbed onto the GO surface.

Detection of promyelocytic leukemia/retinoic acid receptor α (PML/RARα) fusion gene with functionalized graphene oxide

An attempt was made to use functionalized graphene oxide (GO) to detect the Promyelocytic leukemia/Retinoic acid receptor α fusion gene (PML/RARα fusion gene), a marker gene of acute promyelocytic leukemia. The functionalized GO was prepared by chemical exfoliation method, followed by a polyethylene glycol grafting. It is found that the functionalized GO can selectively adsorb the fluorescein isothiocyanate (FITC)-labeled single-stranded DNA probe and quench its fluorescence. The probe can be displaced by the PML/RARα fusion gene to restore the fluorescence, which can be detected by laser confocal microscopy and flow cytometry. These can be used to detect the presence of the PML/RARα fusion gene. This detection method is verified to be fast, simple and reliable.

Three dimensional macroporous architectures and aerogels built of carbon nanotubes and/or graphene: synthesis and applications

Carbon nanotubes and graphene are some of the most intensively explored carbon allotropes in materials science. This interest mainly resides in their unique properties with electrical conductivities as high as 10(4) S cm(-1), thermal conductivities as high as 5000 W m(-1) K and superior mechanical properties with elastic moduli on the order of 1 TPa for both of them. The possibility to translate the individual properties of these monodimensional (e.g. carbon nanotubes) and bidimensional (e.g. graphene) building units into two-dimensional free-standing thick and thin films has paved the way for using these allotropes in a number of applications (including photocatalysis, electrochemistry, electronics and optoelectronics, among others) as well as for the preparation of biological and chemical sensors. More recently and while recognizing the tremendous interest of these two-dimensional structures, researchers are noticing that the performance of certain devices can experience a significant enhancement by the use of three-dimensional architectures and/or aerogels because of the increase of active material per projected area. This is obviously the case as long as the nanometre-sized building units remain accessible so that the concept of hierarchical three-dimensional organization is critical to guarantee the mass transport and, as consequence, performance enhancement. Thus, this review aims to describe the different synthetic processes used for preparation of these three-dimensional architectures and/or aerogels containing either any or both allotropes, and the different fields of application in which the particular structure of these materials provided a significant enhancement in the efficacy as compared to their two-dimensional analogues or even opened the path to novel applications. The unprecedented compilation of information from both CNT- and graphene-based three-dimensional architectures and/or aerogels in a single revision is also of interest because it allows a straightforward comparison between the particular features provided by each allotrope.

Incorporating graphene oxide and gold nanoclusters: a synergistic catalyst with surprisingly high peroxidase-like activity over a broad pH range and its application for cancer cell detection

A synergistic graphene oxide-gold nanocluster (GO-AuNC) hybrid has been constructed as an enzyme mimic that is able to show high catalytic activity over a broad pH range, especially at neutral pH. Importantly, the target-functionalized hybrid has been applied as a robust nanoprobe for selective, quantitative, and fast colorimetric detection of cancer cells.

Graphene oxide-silver nanocomposite as a highly effective antibacterial agent with species-specific mechanisms

Recently, graphene oxide (GO) based nanocomposites have raised significant interests in many different areas, one of which being antibacterial agents where sliver nanoparticle (AgNPs) anchored GO (GO-Ag) has shown promising potential. However, to our best knowledge, factors affecting its antibacterial activity as well as the underlying mechanism remain unclear. In this study, we fabricate GO-Ag nanocomposites with different AgNPs to GO ratios and carefully investigate their antibacterial activities against both the Gram-negative (G-) bacteria Escherichia coli ( E. coli ) and the Gram-positive (G+) bacteria Staphylococcus aureus ( S. aureus ). We discover that, compared to AgNPs, GO-Ag nanocomposite with an optimal ratio of AgNPs to GO is much more effective and shows synergistically enhanced, strong antibacterial activities at rather low dose (2.5 μg/mL). The GO-Ag nanocomposite is more toxic to E. coli than that to S. aureus . The antibacterial effects of GO-Ag nanocomposite are further investigated, revealing distinct, species-specific mechanisms. The results demonstrate that GO-Ag nanocomposite functions as a bactericide against the G- E. coli through disrupting bacterial cell wall integrity, whereas it exhibits bacteriostatic effect on the G+ S. aureus by dramatically inhibiting cell division. Our work not only highlights the great promise of using GO-Ag as a highly effective antibacterial agent but also provides more in-depth understandings of the interactions between microorganisms and GO-based nanocomposites.

Ionic liquid as an efficient modulator on artificial enzyme system: toward the realization of high-temperature catalytic reactions

Herein, with the aid of ionic liquid, we demonstrate for the first time that highly stable Au/SiO2 hetero-nanocomposites can serve as a robust and recyclable peroxidase mimic for realizing high-temperature catalytic reactions. Our findings pave the way to use nanomaterials for the design and development of efficient biomimetic catalysts and, more significantly, to apply ionic liquid as a positive modulator in catalytic reactions.

Functionalization of graphene oxide generates a unique interface for selective serum protein interactions

Potential toxicity and risk of inducing allergy and inflammation have always been a great concern of using nanomaterials in biomedicine. In this work, we investigate the serum behaviors of graphene oxide (GO) and how such behaviors are affected by its surface modification such as PEGylation. The results show that, when incubated with human sera, unfunctionalized GO adsorbs a significant amount of serum proteins and strongly induces complement C3 cleavage (part of the complement activation cascade), generating C3a/C3a(des-Arg), an anaphylatoxin involved in local inflammatory responses, whereas PEGylated nano-GO (nGO-PEG) exhibits dramatic reductions in both protein binding in general and complement C3 activation. Moreover, we uncover that PEGylation on GO nanosheets apparently generates an interesting nanointerface, evidenced by the acquired certain selectivity and increased binding capacities of nGO-PEG toward a few serum proteins. Further mass spectrometry analysis identifies six nGO-PEG binding proteins, four of which are immune-related factors, including C3a/C3a(des-Arg). A series of Western blot analysis demonstrate that nGO-PEG binds up to 2-fold amount of C3a/C3a(des-Arg) than unfunctionalized GO, and can efficiently decrease the level of C3a/C3a(des-Arg) in treated sera, preventing the normal interaction of C3a with its receptor. In a proof-of-concept experiment, we demonstrate that nGO-PEG may serve to help eliminate the C3a/C3a(des-Arg) induced by other nanomaterials such as as-made GO, indicating a new strategy to modulate the immune responses evoked by one nanomaterial through the addition of another type of nanomaterial. Our results highlight the great importance of nanobio interface in regulating the biological effects of nanomaterials.