Assembly of graphene oxide-enzyme conjugates through hydrophobic interaction

A simple chemiluminescent method for the quantification of exosomes based on horseradish peroxidase adsorbed on two-dimensional nanomaterials

The development of simple methods for the isolation and quantification of exosomes in biological samples is important. By using the typical two-dimensional (2D) nanomaterials, graphene oxide (GO), the present work first studied the interaction of liposomes with the nanocomposites formed by adsorbing HRP on the GO surface and found the presence of liposomes led to the release of HRP from the GO surface to the solution phase triggering the luminol-H2O2 chemiluminescence (CL) reaction to emit light. Benefiting from the similarity of exosomes to liposomes in both composition and morphology aspects, the GO-HRP nanocomposites with a mass ratio of 120:1 and 160:1 were employed for the quantitative detection of exosomes in 100-fold diluted serum samples. The whole detection process took about 15 min and as low as 3.2 × 102 particles μL-1 of exosomes could be sensitively detected. In addition to GO-HRP nanocomposites, the CL responses of other nanocomposites obtained from adsorbing HRP on other 2D nanomaterials such as layered MoS2 for exosomes were also tested. MoS2-HRP exhibited similar behavior and the LODs for the detection of exosomes were 5.8 × 102 particles μL-1. The proposed assays were a biomarker-independent quantitative method that achieved the quantification of exosomes in serum samples directly without an isolation process.

Background-filtered telomerase activity assay with cyclic DNA cleavage amplification

Overexpression of telomerase incites the abnormal proliferation of cancer cells. Thus, it has been regarded as a cancer biomarker and a potential therapeutic target. Existing assays suggest a promising sensing scheme to detect telomerase activity. However, they are complicated in terms of assay preparation and implementation. We herein report a Quenching-Exempt invader Signal Amplification Test, termed 'QUEST'. The assay leverages on a high turnover, specific cleaving enzyme, flap endonuclease I (FEN1), and graphene oxide (GO) for background (BG) filtering. In response to the target, FEN1 significantly boosts the signal with invader signal amplification. To distinguish the target signal, GO filters out the BG. It captures residual reporter invader probes (RP) to quench undesired signals. QUEST is straightforward without any pre-preparatory steps and washing/separation. Its probe design is simple and cost-effective. With QUEST, we investigated telomerase activities in various cell lines. Notably, we discriminated cancer cell lines from normal cell lines. In addition, a candidate inhibitor for telomerase was screened, which showed the promising potential of QUEST in real applications.

Injectable hydrogel based on silk fibroin/carboxymethyl cellulose/agarose containing polydopamine functionalized graphene oxide with conductivity, hemostasis, antibacterial, and anti-oxidant properties for full-thickness burn healing

Overcoming bacterial infections and promoting wound healing are significant challenges in clinical practice and fundamental research. This study developed a series of enzymatic crosslinking injectable hydrogels based on silk fibroin (SF), carboxymethyl cellulose (CMC), and agarose, with the addition of polydopamine functionalized graphene oxide (GO@PDA) to endow the hydrogel with suitable conductivity and antimicrobial activity. The hydrogels exhibited suitable gelation time, stable mechanical and rheological properties, high water absorbency, and hemostatic properties. Biocompatibility was also confirmed through various assays. After loading the antibiotic vancomycin hydrochloride, the hydrogels showed sustained release and good antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). The fast gelation time and desirable tissue-covering ability of the hydrogels allowed for a good hemostatic effect in a rat liver trauma model. In a rat full-thickness burn wound model, the hydrogels exhibited an excellent treatment effect, leading to significantly enhanced wound closure, collagen deposition, and granulation tissue formation, as well as neovascularization and anti-inflammatory effects. In conclusion, the antibacterial electroactive injectable hydrogel dressing, with its multifunctional properties, significantly promoted the in vivo wound healing process, making it an excellent candidate for full-thickness skin wound healing.

Nanobio Interface Between Proteins and 2D Nanomaterials

Two-dimensional (2D) nanomaterials have significantly contributed to recent advances in material sciences and nanotechnology, owing to their layered structure. Despite their potential as multifunctional theranostic agents, the biomedical translation of these materials is limited due to a lack of knowledge and control over their interaction with complex biological systems. In a biological microenvironment, the high surface energy of nanomaterials leads to diverse interactions with biological moieties such as proteins, which play a crucial role in unique physiological processes. These interactions can alter the size, surface charge, shape, and interfacial composition of the nanomaterial, ultimately affecting its biological activity and identity. This review critically discusses the possible interactions between proteins and 2D nanomaterials, along with a wide spectrum of analytical techniques that can be used to study and characterize such interplay. A better understanding of these interactions would help circumvent potential risks and provide guidance toward the safer design of 2D nanomaterials as a platform technology for various biomedical applications.

Electrochemical Fine-Tuning of the Chemoresponsiveness of Langmuir-Blodgett Graphene Oxide Films

Graphene oxide has been widely deployed in electrical sensors for monitoring physical, chemical, and biological processes. The presence of abundant oxygen functional groups makes it an ideal substrate for integrating biological functional units to assemblies. However, the introduction of this type of defects on the surface of graphene has a deleterious effect on its electrical properties. Therefore, adjusting the surface chemistry of graphene oxide is of utmost relevance for addressing the immobilization of biomolecules, while preserving its electrochemical integrity. Herein, we describe the direct immobilization of glucose oxidase onto graphene oxide-based electrodes prepared by Langmuir-Blodgett assembly. Electrochemical reduction of graphene oxide allowed to control its surface chemistry and, by this, regulate the nature and density of binding sites for the enzyme and the overall responsiveness of the Langmuir-Blodgett biofilm. X-ray photoelectron spectroscopy, surface plasmon resonance, and electrochemical measurements were used to characterize the compositional and functional features of these biointerfaces. Covalent binding between amine groups on glucose oxidase and epoxy and carbonyl groups on the surface of graphene oxide was successfully used to build up stable and active enzymatic assemblies. This approach constitutes a simple, quick, and efficient route to locally address functional proteins at interfaces without the need for additives or complex modifiers to direct the adsorption process.

Polymer/Graphene Nanocomposites via 3D and 4D Printing—Design and Technical Potential

Graphene is an important nanocarbon nanofiller for polymeric matrices. The polymer–graphene nanocomposites, obtained through facile fabrication methods, possess significant electrical–thermal–mechanical and physical properties for technical purposes. To overcome challenges of polymer–graphene nanocomposite processing and high performance, advanced fabrication strategies have been applied to design the next-generation materials–devices. This revolutionary review basically offers a fundamental sketch of graphene, polymer–graphene nanocomposite and three-dimensional (3D) and four-dimensional (4D) printing techniques. The main focus of the article is to portray the impact of 3D and 4D printing techniques in the field of polymer–graphene nanocomposites. Polymeric matrices, such as polyamide, polycaprolactone, polyethylene, poly(lactic acid), etc. with graphene, have been processed using 3D or 4D printing technologies. The 3D and 4D printing employ various cutting-edge processes and offer engineering opportunities to meet the manufacturing demands of the nanomaterials. The 3D printing methods used for graphene nanocomposites include direct ink writing, selective laser sintering, stereolithography, fused deposition modeling and other approaches. Thermally stable poly(lactic acid)–graphene oxide nanocomposites have been processed using a direct ink printing technique. The 3D-printed poly(methyl methacrylate)–graphene have been printed using stereolithography and additive manufacturing techniques. The printed poly(methyl methacrylate)–graphene nanocomposites revealed enhanced morphological, mechanical and biological properties. The polyethylene–graphene nanocomposites processed by fused diffusion modeling have superior thermal conductivity, strength, modulus and radiation- shielding features. The poly(lactic acid)–graphene nanocomposites have been processed using a number of 3D printing approaches, including fused deposition modeling, stereolithography, etc., resulting in unique honeycomb morphology, high surface temperature, surface resistivity, glass transition temperature and linear thermal coefficient. The 4D printing has been applied on acrylonitrile-butadiene-styrene, poly(lactic acid) and thermosetting matrices with graphene nanofiller. Stereolithography-based 4D-printed polymer–graphene nanomaterials have revealed complex shape-changing nanostructures having high resolution. These materials have high temperature stability and high performance for technical applications. Consequently, the 3D- or 4D-printed polymer–graphene nanocomposites revealed technical applications in high temperature relevance, photovoltaics, sensing, energy storage and other technical fields. In short, this paper has reviewed the background of 3D and 4D printing, graphene-based nanocomposite fabrication using 3D–4D printing, development in printing technologies and applications of 3D–4D printing.

A comprehensive review on bio-mimicked multimolecular frameworks and supramolecules as scaffolds for enzyme immobilization

Immobilization depicts a propitious route to optimize the catalytic performances, efficient recovery, minimizing autocatalysis, and also augment the stabilities of enzymes, particularly in unnatural environments. In this opinion, supramolecules and multimolecular frameworks have captivated immense attention to achieve profound controllable interactions between enzyme molecules and well-defined natural or synthetic architectures to yield protein bioconjugates with high accessibility for substrate binding and enhanced enantioselectivities. This scholastic review emphasizes the possibilities of associating multimolecular complexes with biological entities via several types of interactions, namely covalent interactions, host-guest complexation, π - π ${\rm{\pi }}-{\rm{\pi }}$ interactions, intra/inter hydrogen bondings, electrostatic interactions, and so forth offers remarkable applications for the modulations of enzymes. The potential synergies between artificial supramolecular structures and biological systems are the primary concern of this pedagogical review. The majority of the research primarily focused on the dynamic biomolecule-responsive supramolecular assemblages and multimolecular architectures as ideal platforms for the recognition and modulation of proteins and cells. Embracing sustainable green demeanors of enzyme immobilizations in a quest to reinforce site-selectivity, catalytic efficiency, and structural integrality of enzymes are the contemporary requirements of the biotechnological sectors that instigate the development of novel biocatalytic systems.

Graphene quantum dots induce cascadic apoptosis via interaction with proteins associated with anti-oxidation after endocytosis by Trypanosoma brucei

Trypanosoma brucei, the pathogen causing African sleeping sickness (trypanosomiasis) in humans, causes debilitating diseases in many regions of the world, but mainly in African countries with tropical and subtropical climates. Enormous efforts have been devoted to controlling trypanosomiasis, including expanding vector control programs, searching for novel anti-trypanosomial agents, and developing vaccines, but with limited success. In this study, we systematically investigated the effect of graphene quantum dots (GQDs) on trypanosomal parasites and their underlying mechanisms. Ultrasmall-sized GQDs can be efficiently endocytosed by T. brucei and with no toxicity to mammalian-derived cells, triggering a cascade of apoptotic reactions, including mitochondrial disorder, intracellular reactive oxygen species (ROS) elevation, Ca²⁺ accumulation, DNA fragmentation, adenosine triphosphate (ATP) synthesis impairment, and cell cycle arrest. All of these were caused by the direct interaction between GQDs and the proteins associated with cell apoptosis and anti-oxidation responses, such as trypanothione reductase (TryR), a key protein in anti-oxidation. GQDs specifically inhibited the enzymatic activity of TryR, leading to a reduction in the antioxidant capacity and, ultimately, parasite apoptotic death. These data, for the first time, provide a basis for the exploration of GQDs in the development of anti-trypanosomials.

Protein sustained release from isobutyramide-grafted stellate mesoporous silica nanoparticles

Proteins are great therapeutic candidates as endogenous biomolecules providing a wide range of applications. However, their delivery suffers from some limitations and specifically designed delivery systems having an efficient protein anchoring and delivery strategy are still needed. In this work, we propose to combine large pore stellate mesoporous silica (STMS) with isobutyramide (IBAM), as a "glue" molecule which has been shown promising for immobilization of various biomacromolecules at silica surface. We address here for the first time the ability of such IBAM-modified NPs to sustainably deliver proteins over a prolonged time. In this work, a quantitative loading study of proteins (serum albumin (HSA), peroxidase (HRP), immunoglobulin (IgG) and polylysine (PLL)) on STMS@IBAM is first presented using three complementary detection techniques to ensure precision and avoid protein quantification issues. The results demonstrated a high loading capacity for HSA and HRP (≥ ca. 350 μg.mg-1) but a moderate one for IgG and PLL. After evaluating the physicochemical properties of the loaded particles and their stability over scaling-up and washings, the ability of STMS@IBAM to release proteins over prolonged time was evaluated in equilibrium (static) and flow mimicking (dynamic) conditions and at different temperatures (25, 37, 45 °C). Results show not only the potential of such "glue" functionalized STMS to release proteins in a sustained way, but also the retention of the biological activity of immobilized and released HRP, used as an enzyme model. Finally, an AFM-force spectroscopy study was conducted to decipher the interactions between IBAM and proteins, showing the involvement of different interactions in the adsorption and release processes.

Jinghua Weikang capsule for helicobacter pylori eradication: A systematic review and meta-analysis with trial sequential analysis

Background: Helicobacter pylori (H. pylori) infection is one of the most common chronic bacterial infections worldwide. The resistance of H. pylori to antibiotics may increase the risk of treatment failure. Complementary and alternative regimens are still needed. This study aimed to critically assess the efficacy and safety of Jinghua Weikang capsule (JWC) for H. pylori eradication. Materials and methods: PubMed, Embase, Web of Science, Cochrane library, China National Knowledge Infrastructure, Wanfang Digital Periodicals, and Chinese Science and Technology Periodicals database were searched from inception to April 2022. Randomized controlled trials (RCTs) comparing a combination of JWC and conventional treatments with conventional treatments alone or combined with a placebo for H. pylori eradication were considered for inclusion. The primary outcome was H. pylori eradication rate. The meta-analysis and trial sequential analysis (TSA) were conducted where possible. Results: A total of 34 studies were included in the statistical analysis. A pooled result showed that JWC with the duration of 2 weeks combined with the triple/quadruple therapy could significantly increase the H. pylori eradication rate compared with the triple/quadruple therapy alone (RR: 1.13, 95% CI: 1.05 to 1.21, p = 0.0008). However, the evidence of benefit was not confirmed by TSA. Another pooled result showed that JWC with the duration of 4 weeks combined with the triple/quadruple therapy could significantly increase the H. pylori eradication rate compared with the triple/quadruple therapy alone (RR: 1.21, 95% CI: 1.15 to 1.27, p < 0.00001). The evidence of benefit was confirmed by TSA. There were no statistically significant differences in the incidence of adverse reactions between the two groups. Conclusion: The present study suggests that JWC with the duration of 4 weeks can significantly improve the H. pylori eradication rate and should be considered as a complementary treatment to conventional regimens for H. pylori eradication. However, more high-quality RCTs are still needed to confirm these findings.

Nanoarmored Multi-Enzyme Cascade Catalysis

This chapter reports a single-step preparation of nanoarmored bi-enzyme systems assembled on 1-D and 2-D nanomaterials, with glucose oxidase and peroxidase enzymes as model systems for cascade bio-catalysis. This is a simple and facile method to both exfoliate the bulk 1D (carbon nanotubes, CNT) and 2D nanomaterials (α-Zirconium phosphate, α-ZrP) and bind the enzymes in a single step. Exfoliation of the bulk material enhances the accessible surface area of the materials for the enzyme binding, and it also boosts the diffusion of reagents from the bulk phase to the active sites of the bio-catalysts. For example, a mixture of horseradish peroxidase, glucose oxidase, and bovine serum albumin (BSA) were adsorbed on the surfaces of the α-ZrP nanoplates or carbon nanotubes (CNT) as the bulk materials are exfoliated simultaneously, in a one-step process. The resulting bio-catalysts were thoroughly characterized by powder X-ray diffraction, electron microscopy, biochemical and biophysical methods, while enzyme activity studies proved successful binding of enzymes with retention of activities or even enhancements in their specific activities. For example, GOx/HRP/BSA/CNT displayed 6 times the activity of a mixture of GOx/HRP/BSA, under otherwise identical conditions. Similarly, GOx/HRP/BSA/ZrP had 3.5 times the activity of the corresponding mixture of GOx/HRP/BSA, in the absence of the nanoplates. These robust nano-dispersions worked extraordinarily well as active bio-catalysts. These two kinds of fabricated biocatalyst dispersions are also highly stable.

Enzyme-catalyzed cascade reactions on multienzyme proteinosomes

In this research, to mimic the structures and the functionalities of the organelles in living cells multienzyme proteinosomes with β-galactosidase (β-gal), glucose oxidase (GOx) and horseradish peroxidase (HRP) on the surfaces are fabricated by hydrophobic-interaction induced self-assembly approach. To investigate the mechanism of the formation of proteinosomes, poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) and bovine serum albumin are employed in a model system and the study demonstrates that the hydrophobic interaction between the dehydrated polymer chains and the hydrophobic patches on the proteins plays a key role in the fabrication of the proteinosomes. Based on the model system, multienzyme proteinosomes with β-gal, GOx and HRP on the surfaces are fabricated through hydrophobic interaction between PDEGMA and enzyme molecules. Enzyme-catalyzed cascade reactions are performed on the surfaces of the proteinosomes, and the immobilized enzymes show higher bioactivities than the "free" enzymes, due to the direct transfer of the product as a substrate from one enzyme molecule to another. This research provides a unique method for the synthesis of multienzyme proteinosomes with improved bioactivities, and the biofunctional structures will find promising applications in medical and biological science.

Surface Modulation of Graphene Oxide for Amidase Immobilization with High Loadings for Efficient Biocatalysis

As a type of important and versatile biocatalyst, amidase immobilization on solid materials has received broad attention with its relatively easy procedure and available reusability. However, current porous supports have suffered from limited loadings, and it is highly desired to develop a new type of material with abundant space so as to ensure a high loading of amidase. Here, graphene oxide was adopted as the support for amidase immobilization, which showed the highest loading capacity for amidase (~3000 mg/g) to date. To the best of our knowledge, it is the first case of amidase immobilized on graphene oxide. Through surface modulation via reducing the contents of oxygen-containing functional groups, activity recovery of immobilized amidase increased from 67.8% to 85.3%. Moreover, surface-modulated graphene oxide can efficiently uptake amidase under a wide range of pH, and the maximum loading can reach ~3500 mg/g. The resultant biocomposites exhibit efficient biocatalytic performance for asymmetric synthesis of a chiral amino acid (i.e., L-4-fluorophenylglycine, an intermediate of aprepitant).

Evaluation of Utilizing Functionalized Graphene Oxide Nanoribbons as Compatible Biomaterial for Lysozyme

Graphene oxide nanoribbons with superior physicochemical properties acquired from graphene and carbon nanotubes have been used in various applications including biomedical applications. For biomedical applications, it is of utmost importance to understand how these graphene oxide nanoribbons interact with proteins and the influence they have on protein conformation and function. In this regard, an attempt has been made to evaluate the utility of graphene oxide nanoribbons as a compatible biomaterial for lysozyme (Lys) protein. In this study, graphene oxide nanoribbons (GONRs) synthesized from multiwalled carbon nanotubes (MWCNTs) were first functionalized with (3-aminopropyl)triethoxysilane (APTES) and further modified with vanillin (Val) to obtain Val-APTES-GONRs. On characterization, it was found that the Val-APTES-GONRs material had a ribbonlike morphology with abundant functionalities for interaction with protein. On evaluation of Val-APTES-GONRs as a compatible biomaterial for Lys, studies revealed that a lower concentration of the as-synthesized material has less influence on the conformation and the structure of Lys with better activity, whereas higher concentrations of the as-synthesized material had a greater influence on conformation and the structure of Lys with decreased activity. Overall, the thermal stability of Lys was maintained after introducing the Val-APTES-GONRs material. In addition, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and Raman spectroscopies were performed for Lys composites with Val-APTES-GONRs for further understanding biomolecular interactions. This study is beneficial for designing advanced graphene-based materials for numerous bioinspired applications and better biomaterials for biotechnological use.

Graphene, Graphene-Derivatives and Composites: Fundamentals, Synthesis Approaches to Applications

Graphene has accomplished huge notoriety and interest from the universe of science considering its exceptional mechanical physical and thermal properties. Graphene is an allotrope of carbon having one atom thick size and planar sheets thickly stuffed in a lattice structure resembling a honeycomb structure. Numerous methods to prepare graphene have been created throughout a limited span of time. Due to its fascinating properties, it has found some extensive applications to a wide variety of fields. So, we believe there is a necessity to produce a document of the outstanding methods and some of the novel applications of graphene. This article centres around the strategies to orchestrate graphene and its applications in an attempt to sum up the advancements that has taken place in the research of graphene.

One-step self-assembly of magnetic supramolecular metal-organic coordination functionalized MoS2 complex as nanoenzyme-reactor

In the present study, a kind of magnetic supramolecular metal-organic coordination complex (SMOCC) functionalized MoS₂ was prepared with one-step in aqueous solution for enzyme immobilization. As possessing a protective nanocoating of PDA/PEI/Cu²⁺ (polydopamine: PDA, polyethyleneimine: PEI), the proposed material can provide biocompatible microenvironment and flexible adhesion force on particle interface, which is conductive to loading laccase (170.0 ± 1.8 mg/g) with high activity (93.0 ± 1.1 %). Compared with the free laccase, the immobilized laccase has higher stability in a broader range of pH (3-10), temperature (20-80 °C), storage time (1-18 days) and reusability (1-16 cycles). The removal of carcinogenic persistent organic pollutant malachite green in the water with the immobilized laccase shows a higher efficiency (89.4 ± 1.2 %) than free laccase (16.2 ± 0.2 %). The Fe₃O₄@MoS₂@(PDA/PEI/Cu²⁺) nanocomposites can also be used successfully to immobilize trypsin, lipase and catalase respectively, showing a satisfactory enzyme loading (157.0 ± 0.1 mg/g, 151.6 ± 1.4 mg/g, 162.6 ± 1.6 mg/g, respectively) and activity (95.0 ± 0.5 %, 90.0 ± 0.8 %, 91.0 ± 0.9 %, respectively). The MoS₂ can be replaced by carbon material and similar results can be obtained.

In situ formation of nanocomposite double-network hydrogels with shear-thinning and self-healing properties

Nanocomposite double-network hydrogels (ncDN hydrogels) are recently introduced to address the limitations of traditional DN hydrogels, such as the lack of diversity in the network structure and the restricted functionalities. However, two challenges remain, including the time-consuming preparation and the lack of shear-thinning and self-healing properties. Here, our approach to developing versatile ncDN hydrogels is through the use of multiple interfacial crosslinking chemistries (i.e., noncovalent interactions of electrostatic interaction and hydrogen bonds as well as dynamic covalent interactions of imine bonds and boronate ester bonds) and surface functionalized nanomaterials (i.e. phenylboronic acid modified reduced graphene oxide (PBA-rGO)). PBA-rGO was used as a multivalent gelator to further crosslink the two polymer chains (i.e. triethylene glycol-grafted chitosan (TEG-CS) and polydextran aldehyde (PDA)) in DN hydrogels, forming the TEG-CS/PDA/PBA-rGO ncDN hydrogels in seconds. The microstructures (i.e. pore size) and properties (i.e. rheological, mechanical, and swelling properties) of the ncDN hydrogels can be simply modulated by changing the amount of PBA-rGO. The dynamic bonds in the polymeric network provided the shear-thinning and self-healing properties to the ncDN hydrogels, allowing the hydrogels to be injected and molded into varied shapes as well as self-repair the damaged structure. Besides, the designed TEG-CS/PDA/PBA-rGO ncDN hydrogels were cytocompatible and also exhibited antibacterial activity. Taken together, we hereby provide a nanomaterial approach to fabricate a new class of ncDN hydrogels with tailorable networks and favorite properties for specific applications.

The interaction of graphene oxide-silver nanoparticles with trypsin: Insights from adsorption behaviors, conformational structure and enzymatic activity investigations

In this work, we synthesized graphene oxide-silver nanoparticles (GO-AgNPs) hybrids by one-pot method. Since there are relatively few reports on whether GO-AgNPs bind and change the structure and function of trypsin, A variety of methods were employed to systematically characterize the molecular interaction between GO-AgNPs and trypsin. Results exhibited that GO-AgNPs bound with trypsin to form a ground state complex. GO-AgNPs had higher adsorption capacity for trypsin compared with single GO. Langmuir-Blodgett assembly method was used to confirm that AgNPs did not interfere with the adsorption of trypsin by GO. The secondary structure and the microenvironment of amino acid residues of trypsin were altered after interacting with GO-AgNPs. In addition, GO-AgNPs can enhance the activity of trypsin and promote the hydrolysis of bovine serum protein (BSA) by trypsin. These findings provide important support for the application of GO-based nanocomposites in the efficient immobilization of enzymes.

Protein immobilization on graphene oxide or reduced graphene oxide surface and their applications: Influence over activity, structural and thermal stability of protein

Due to the essential role of biological macromolecules in our daily life; it is important to control the stability and activity of such macromolecules. Therefore, the most promising route for enhancement in stability and activity is immobilizing proteins on different support materials. Furthermore, large surface area and surface functional groups are the important features that are required for a better support system. These features of graphene oxide (GO) and reduced graphene oxide (RGO) makes them ideal support materials for protein immobilization. Studies show the successful formation of GO/RGO-protein complexes with enhancement in structural/thermal stability due to various interactions at the nano-bio interface and their utilization in various functional applications. The present review focuses on protein immobilization using GO/RGO as solid support materials. Moreover, we also emphasized on basic underlying mechanism and interactions (hydrophilic, hydrophobic, electrostatic, local protein-protein, hydrogen bonding and van der Walls) between protein and GO/RGO which influences structural stability and activity of enzymes/proteins. Furthermore, GO/RGO-protein complexes are utilized in various applications such as biosensors, bioimaging and theranostic agent, targeted drug delivery agents, and nanovectors for drug and protein delivery.

Polymerization-induced proteinosome formation

In recent years, the fabrication of well-organized proteinosomes has been a popular topic due to the potential applications of the structures in materials science and nanotechnology. A big challenge in the fabrication of proteinosomes is to maintain the structures and the functionalities of proteins on the proteinosomes. In this research, a new concept of polymerization-induced formation of proteinosomes is proposed. In thermal dispersion polymerization of N-isopropyl acrylamide (NIPAM) in the presence of bovine serum albumin (BSA), the growing PNIPAM chains experience phase transition from hydrated coils to dehydrated globules, and the dehydrated PNIPAM chains have hydrophobic interaction with BSA, leading to the formation of hollow proteinosomes. Kinetics studies indicate that there is a transition from the homogeneous polymerization of NIPAM in solution to the heterogeneous polymerization in the proteinosomes. Transmission electron microscopy, atomic force microscopy, confocal laser scanning microscopy and dynamic light scattering all demonstrate the formation of hollow structures. The results of circular dichroism spectroscopy indicate that the secondary structure of BSA remains unchanged in the polymerization process. The formation of proteinosomes is reversible. Upon cooling of the solution to a temperature below the phase transition temperature of PNIPAM, the proteinosomes are dissociated due to the absence of the hydrophobic interaction. The proteinosomes can be used in the encapsulation of hydrophilic compounds in aqueous solution. In this research, not only BSA but also ovalbumin (OVA) is used as a model protein for the fabrication of proteinosomes by the polymerization-induced approach.

Hybrid magneto-luminescent iron oxide nanocubes functionalized with europium complexes: synthesis, hemolytic properties and protein corona formation

The use of hybrid nanostructures based on magneto-luminescent properties is a promising strategy for nano-bio applications and theranostics platforms. In this work, we carried out the synthesis and functionalization of iron oxide nanocubes (IONCs) to obtain multifunctional hybrid nanostructures towards biomedical applications. The IONCs were functionalized with tetraethylorthosilicate, thenoyltrifluoroacetone-propyl-triethoxysilane and europium(iii)-dibenzoylmethane complexes to obtain the materials termed as IOCNCs@SiO₂, IONCs@SiO₂TTA, IONCs@SiO₂TTA-Eu and IONCs@SiO₂-TTA-Eu-DBM, respectively. Then, the biological interactions of these nanostructures with red blood cells - RBCs (hemolysis) and human blood plasma (protein corona formation) were evaluated. The XPS spectrocopy and EDS chemical mapping analysis showed that each domain is homogeneously occupied in the hybrid material, with the magnetic core at the center and the luminescent domain on the surface of the hybrid nanomaterial with a core@shell like structure. Futhermore, after each functionalization step, the nanomaterial surface charge drastically changed, with critical impact on RBC lysis and corona formation. While IONCs@SiO₂ and IONCs@SiO₂-TTA-Eu-DBM showed hemolytic properties in a dose-dependent manner, the IONCs@SiO₂TTA-Eu did not present any hemolytic effect up to 300 μg mL^-1. Protein corona results showed a pattern of selective adsorption of proteins with each surface of the synthesized hybrid materials. However, as a general result, a suppression of hemolysis after protein corona formation in all tests was verified. Finally, this study provides a solid background for further applications of these hybrid magneto-luminescent materials containing new surface functionalities in the emerging field of medical nanobiotechnology.

Harnessing the biocatalytic attributes and applied perspectives of nanoengineered laccases-A review

In the recent past, numerous new types of nanostructured carriers, as support matrices, have been engineered to advance the traditional enzyme immobilization strategies. The current research aimed to develop a robust enzyme-based biocatalytic platform and its effective deployment in the industrial biotechnology sectors at large and catalysis area, in particular, as low-cost biocatalytic systems. Suitable coordination between the target enzyme molecules and surface pendent multifunctional entities of nanostructured carriers has led an effective and significant contribution in myriad novel industrial, biotechnological, and biomedical applications. As compared to the immobilization on planar two-dimensional (2-D) surface, the unique physicochemical, structural and functional attributes of nano-engineered matrices, such as high surface-to-volume ratio, surface area, robust chemical and mechanical stability, surface pendant functional groups, outstanding optical, thermal, and electrical characteristics, resulted in the concentration of the immobilized entity being substantially higher, which is highly requisite from applied bio-catalysis perspective. Besides inherited features, nanostructured materials-based enzyme immobilization aided additional features, such as (1) ease in the preparation or green synthesis route, (2) no or minimal use of surfactants and harsh reagents, (3) homogeneous and well-defined core-shell nanostructures with thick enzyme shell, and (4) nano-size can be conveniently tailored within utility limits, as compared to the conventional enzyme immobilization. Moreover, the growing catalytic needs can be fulfilled by multi-enzymes co-immobilization on these nanostructured materials-based support matrices. This review spotlights the unique structural and functional attributes of several nanostructured materials, including carbon nanotubes, graphene, and its derivate constructs, nanoparticles, nanoflowers, and metal-organic frameworks as robust matrices for laccase immobilization. The later half of the review focuses on the applied perspective of immobilized laccases for the degradation of emergent contaminants, biosensing cues, and lignin deconstruction and high-value products.

A Novel and High-Effective Biosynthesis Pathway of Hesperetin-7-O-Glucoside Based on the Construction of Immobilized Rhamnosidase Reaction Platform

Hesperetin-7-O-glucoside (HMG) is a precursor for synthesizing a sweetener named neohesperidin dihydrochalcone, and the coordination toward flavonoids of metal ions tends to increase the water solubility of flavonoids. In order to achieve effective synthesis of HMG, an immobilized enzyme catalysis platform was constructed using an immobilized rhamnosidase on Fe₃O₄@graphene oxide (Fe₃O₄@GO), a novel reaction pathway based on the platform was designed for preparing a hesperidin complex as a soluble substrate, and ammonium hydroxide as a ligand dissociation agent to obtain HMG. The Fe₃O₄@GO was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and thermal methods (TG/DSC) analysis to evaluate the immobilization matrix properties. The enzyme activity in free and immobilized form at different pH and temperature was optimized. The reusability of immobilized enzyme was also determined. In addition, the kinetic parameters (K_m and V_max) were computed after experiment. Results indicated that rhamnosidase immobilized on Fe₃O₄@GO using a green cross-linker of genipin hydrolyzed successfully and selectively the soluble hesperidin-Cu (II) complex into HMG-Cu (II), a permanent magnet helped the separation of immobilized enzyme and hydrolytes, and ammonium hydroxide was an effective ligand dissociation agent of translating HMG-Cu (II) into HMG with high purity determined by ultraviolet-visible (UV-Vis) spectra analysis and time-of-flight mass spectrometry (TOF-MS). As a result, a novel and high-effective biosynthesis pathway of HMG based on a selectively catalytic reaction platform were constructed successfully. The pathway based on the platform has great potential to produce valuable citrus monoglycoside flavonoid HMG, and the designed reaction route are feasible using the hesperidin-Cu (II) complex with good solubility as a reaction substrate and using ammonium water as a dissociation agent.

Self-degrading graphene sheets for tumor therapy

Low biodegradability of graphene derivatives and related health risks are the main limiting factors for their in vivo biomedical applications. Here, we present the synthesis of enzyme-functionalized graphene sheets with self-degrading properties under physiological conditions and their applications in tumor therapy. The synergistic enzyme cascade glucose oxidase and myeloperoxidase are covalently conjugated to the surface of graphene sheets and two-dimensional (2D) platforms are obtained that can produce sodium hypochlorite from glucose. The enzyme-functionalized graphene sheets with up to 289 nm average size are degraded into small pieces (≤40 nm) by incubation under physiological conditions for 24 h. Biodegradable graphene sheets are further loaded with doxorubicin and their ability for tumor therapy is evaluated in vitro and in vivo. The laser-triggered release of doxorubicin in combination with the enzymatic activity of the functionalized graphene sheets results in a synergistic antitumor activity. Taking advantage of their neutrophil-like activity, fast biodegradability, high photo- and chemotherapeutic effects, the novel two-dimensional nanoplatforms can be used for tumor therapeutic applications.

Investigations of conformational structure and enzymatic activity of trypsin after its binding interaction with graphene oxide

Herein, interaction between graphene oxide (GO) and trypsin was systematically characterized for deep investigations of conformational structure and enzymatic activity of trypsin affected by GO. Results indicated that GO bound with trypsin to form ground state complex with molar ratio of 1 to 1. Intrinsic fluorescence of trypsin was statically quenched by GO through van der Waal interaction, hydrophobic interaction, hydrogen bond, and electrostatic interaction. Both tertiary structure and secondary structure of trypsin were changed obviously after its binding with trypsin, resulting in the structure transformation of trypsin from the β-sheet structure to the α-helix structure. Since GO bound with the allosteric site of trypsin to inhibit its enzymatic activity via non-competitive manner, GO efficiently protected human serum albumin and human cervical carcinoma HeLa cells from the digestion of trypsin. These results explored the exact binding mechanism of GO with protease, which provides more important information for possible biological risk of GO on human beings.

In-depth understanding of a nano-bio interface between lysozyme and Au NP-immobilized N-doped reduced graphene oxide 2-D scaffolds

In the present work, nitrogen-doped reduced graphene oxide (NrGO) was synthesized via a hydrothermal treatment of graphene oxide (GO) in the presence of urea. Gold nanoparticles (Au(0) NPs) were immobilized over the surface of NrGO (Au(0)-NrGO). Characterization of the Au(0)-NrGO nanocomposite via FT-IR spectroscopy, Raman spectroscopy, elemental mapping and XPS revealed the doping of N atoms during the reduction of GO. XRD and XPS studies confirmed the presence of Au(0) NPs and EDS analysis showed a 4.51 wt% loading of Au NPs in the Au(0)-NrGO nanocomposite. The morphology of Au(0)-NrGO was explored by SEM and TEM, which showed the presence of spherical Au metal NPs uniformly immobilized on the surface of NrGO. Further, studies on lysozyme (Lys) in the presence of Au(0)-NrGO by UV-visible, fluorescence, and circular dichroism spectroscopy revealed a conformational change in Lys and electrostatic interaction between Lys and Au(0)-NrGO. The DLS result showed an enhancement in the size of the Au(0)-NrGO and Lys conjugates. The Au(0)-NrGO-induced conformational changes in the structure of Lys resulted in a significant decrease in its activity at a certain concentration of Au(0)-NrGO. Moreover, the results showed that Lys favorably binds with the surface of Au(0)-NrGO, resulting in the formation of 2-D scaffolds possibly due to electrostatic and hydrophobic interactions, H-bonding, and interactions between the AuNPs and sulfur-containing amino acid residues of Lys. SEM exhibited the formation of conjugates in the form of 2-D scaffolds due to the biomolecular interactions between Lys and Au(0)-NrGO. The TEM studies revealed that Lys agglomerated around the Au(0) NPs immobilized on the surface of NrGO, which suggests the formation of a protein corona (PC) around the AuNPs. Furthermore, the favorable Au(0) NP-sulphur (PC) interaction was confirmed by the disappearance of the S-S stretching band in the Raman spectra. Overall, the results obtained provide insight into the nano-bio interface and formation of Au(0) NP-PC, which can be used for bioinspired applications, such as biosensing and imaging and the development of advanced functional Au NPs.

Laccase Immobilized Fe3O4-Graphene Oxide Nanobiocatalyst Improves Stability and Immobilization Efficiency in the Green Preparation of Sulfa Drugs

This paper, reports on the novel and green synthesis procedure for sulfonamides that involved the immobilization of Trametes Versicolor laccase onto the Fe3O4–graphene nanocomposite via glutaraldehyde (GA) crosslinking (Lac/Fe3O4/GO). Various parameters, mainly, activation time, GA, and laccase concentration were investigated and optimized. The results showed that the optimal contact time was 4 h, GA concentration was 5% while laccase concentration was 5 mg·mL−1, at which a high enzyme activity recovery was achieved (86%). In terms of the stability of immobilized laccase to temperature and storage conditions, the performance of the nanobiocatalyst was found to significantly exceed that of free laccase. The results have indicated that nearly 70% of relative activity for immobilized laccase remained after the incubation period of 2 h at 55 °C, but only 48% of free laccase remained within the same time period. Moreover, the immobilized laccase retained 88% of its initial activity after storage for 20 days. In case of the free laccase, the activity retained within the same time period was 32%. In addition, the nanobiocatalyst possessed better recycling performance as evidenced from the observation that after eight cycles of repeated use, it retained 85% of its original activity.

Engineering functional inorganic nanobiomaterials: controlling interactions between 2D-nanosheets and enzymes

A better understanding of the enzyme-nanosheet interface is imperative for the design of functional, robust inorganic nanobiomaterials and biodevices, now more than ever, for use in a broad spectrum of applications. This feature article discusses recent advances in controlling the enzyme-nanosheet interface with regards to α-zirconium(iv) phosphate (α-ZrP), graphene oxide (GO), graphene, and MoS₂ nanosheets. Specific focus will be placed on understanding the mechanisms with which these materials interact with enzymes and elaborate on particular ways to engineer and control these interactions. Our main discoveries include: (1) upon adsorption to the nanosheet surface, a decrease in the entropy of the enzyme's denatured state enhances stability; (2) proteins are used to create biophilic landing pads for increased enzyme stability on many different types of nanosheets; (3) proteins and enzymes are used as exfoliants by shear force to produce biofunctionalized nanosheet suspensions; and (4) bionfunctionalized nanosheets exhibit no acute toxicity. Recognizing proper methods to engineer the interface between enzymes and 2D-nanosheets, therefore, is an important step towards making green, sustainable, and environmentally conscious inorganic bionanomaterials for sensing, catalysis and drug delivery applications, as well as towards the successful manipulation of enzymes for advanced applications.

Design and Preparation of Carbon Nitride-Based Amphiphilic Janus N-Doped Carbon/MoS2 Nanosheets for Interfacial Enzyme Nanoreactor

Janus amphiphilic particles have gained much attention for their important application value in areas as diverse as interfacial modification, sensors, drug delivery, optics, and actuators. In this work, we prepared Janus amphiphilic nanosheets composed of nitrogen-doped stratiform meso-macroporous carbons (NMC) and molybdenum sulfide (MoS₂) for hydrophilic and hydrophobic sides, respectively. The dicyandiamide and glucose were used as precursors for synthesizing two-dimensional nitrogen-doped meso-macroporous carbons, and the molybdate could be anchored by the functional groups on the surface of carbon layers and then transform into uniformly MoS₂ to form the Janus amphiphilic layer by layer NMC/MoS₂ support. Transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to demonstrate the successful preparation of Janus materials. As the typical interfacial enzyme, Candida rugosa lipase (CRL) immobilized on the Janus amphiphilic NMC/MoS₂ support brought forth to improvement of its performance because the Janus nanosheets can be easily attached on the oil-aqueous interface for better catalytic activity (interfacial activation of lipases). The obtained immobilized lipase (NMC/MoS₂@CRL) exhibited satisfactory lipase loading (193.1 mg protein per g), specific hydrolytic activity (95.76 U g^-1), thermostability (at 55 °C, 84% of the initial activity remained after 210 min), pH flexibility, and recyclability (60% of the initial activity remained after nine runs). In terms of its application, the esterification rate of using NMC/MoS₂@CRL (75%) is higher than those of NMC@CRL (20%) and MoS₂@CRL (11.8%) in the "oil-water" biphase and CRL as well as NMC/MoS₂@CRL in the one-phase. Comparing with the free CRL, NMC@CRL, and MoS₂@CRL, the Janus amphiphilic NMC/MoS₂ served as a carrier that exhibited more optimal performance and practicability.

A Review of Theranostics Applications and Toxicities of Carbon Nanomaterials

BACKGROUND

In the last few years, the use of modified Carbon Nanomaterials (CNMs) for theranostics (therapeutic and diagnosis) applications is a new and rapidly growing area in pharmacy and medical fields. Owing to this, their specific physicochemical behaviors like high stability, drug loading, surface area to volume ratio, with low toxicity and immunogenicity are mainly responsible to be considered those as smart nanomaterials.

OBJECTIVES

This review describes the different dimensions of carbon-based nanocarriers including 0-D fullerene, 1-D Carbon Nanotubes (CNTs), and 2-D graphene and Graphene Oxide (GO) and their surface modification with different biocompatible and biodegradable molecules via covalent or non-covalent functionalization. The major focus of this article is on the different theranostics applications of CNMs like targeted drugs and genes delivery, photodynamic therapy, photothermal therapy, bioimaging, and biosensing. The therapeutic efficacy of drugs could be enhanced by delivering them directly on a specific site using different targeted ligands such as vitamins, peptide, carbohydrates, proteins, etc. A section of the article also discusses the toxicity of the CNMs to the living systems.

CONCLUSIONS

In brief, this review article discusses the numerous theranostics applications and toxicities of CNMs.

Interaction Analysis of Commercial Graphene Oxide Nanoparticles with Unicellular Systems and Biomolecules

The ability of commercial monolayer graphene oxide (GO) and graphene oxide nanocolloids (GOC) to interact with different unicellular systems and biomolecules was studied by analyzing the response of human alveolar carcinoma epithelial cells, the yeast Saccharomyces cerevisiae and the bacteria Vibrio fischeri to the presence of different nanoparticle concentrations, and by studying the binding affinity of different microbial enzymes, like the α-l-rhamnosidase enzyme RhaB1 from the bacteria Lactobacillus plantarum and the AbG β-d-glucosidase from Agrobacterium sp. (strain ATCC 21400). An analysis of cytotoxicity on human epithelial cell line A549, S. cerevisiae (colony forming units, ROS induction, genotoxicity) and V. fischeri (luminescence inhibition) cells determined the potential of both nanoparticle types to damage the selected unicellular systems. Also, the protein binding affinity of the graphene derivatives at different oxidation levels was analyzed. The reported results highlight the variability that can exist in terms of toxicological potential and binding affinity depending on the target organism or protein and the selected nanomaterial.

3D-printed graphene direct electron transfer enzyme biosensors

Three-dimensional (3D) printing technology offers attractive possibilities for many fields. In electrochemistry, 3D printing technology has been used to fabricate customized 3D-printed electrodes as a platform to develop bio/sensing, energy generation and storage devices. Here, we use a 3D-printed graphene/polylactic (PLA) electrode made by additive manufacturing technology and immobilize horseradish peroxidase (HRP) to create a direct electron transfer enzyme-based biosensors for hydrogen peroxide detection. Gold nanoparticles are included in the system to confirm and facilitate heterogeneous electron transfer. This work opens a new direction for the fabrication of third-generation electrochemical biosensors using 3D printing technology, with implications for applications in the environmental and biomedical fields.

Biosynthetic Electronic Interfaces for Bridging Microbial and Inorganic Electron Transport

Electron transport in biological and inorganic systems is mediated through distinct mechanisms and pathways. Their fundamental mismatch in structural and thermodynamic properties has imposed a significant challenge on the effective coupling at the biotic/abiotic interface, which is central to the design and development of bioelectronic devices and their translation toward various engineering applications. Using electrochemically active bacteria, such as G. sulfurreducens, as a model system, here we report a bottom-up, biosynthetic approach to synergize the electron transport and significantly enhance the coupling at the heterogeneous junction. In particular, graphene oxide was exploited as the respiratory electron acceptors, which can be directly reduced by G. sulfurreducens through extracellular electron transfer, closely coupled with outer membrane cytochromes in electroactive conformation, and actively "wire" the redox centers to external electrical contacts. Through this strategy, the contact resistance at the biofilm/electrode interface can be effectively reduced by 90%. Furthermore, the cyclic voltammetry reveals that the electron transfer of the DL-1 biofilm transformed from a low-current (∼0.36 μA), rate-limited profile to a high-current (∼5 μA), diffusion-limited profile. These results suggested that the integration of rGO can minimize the charge transfer barriers at the biofilm/electrode interface. The more transparent contact at the DL-1/electrode interface also enables unambiguous characterization of the inherent electron transport kinetics across the electroactive biofilm independent of cell/electrode interactions. The current work represents a strategically new approach toward the seamless integration of biological and artificial electronics, which is expected to provide critical insights into the fundamentals of biological electron transport and open up new opportunities for applications in biosensing, biocomputing, and bioenergy conversion.

A review on peptide functionalized graphene derivatives as nanotools for biosensing

Peptides exhibit unique binding behavior with graphene and its derivatives by forming bonds on its edges and planes. This makes them useful for sensing and imaging applications. This review with (155 refs.) summarizes the advances made in the last decade in the field of peptide-GO bioconjugation, and the use of these conjugates in analytical sciences and imaging. The introduction emphasizes the need for understanding the biotic-abiotic interactions in order to construct controllable peptide-functionalized graphitic material-based nanotools. The next section covers covalent and non-covalent interactions between peptide and oxidized graphene derivatives along with a discussion of the adsorption events during interfacing. We then describe applications of peptide-graphene conjugates in bioassays, with subsections on (a) detection of cancer cells, (b) monitoring protease activity, (c) determination of environmental pollutants and (d) determination of pathogenic microorganisms. The concluding section describes the current status of peptide functionalized graphitic bioconjugates and addresses future perspectives. Graphical abstractSchematic representation depicting biosensing applications of peptide functionalized graphene oxide.

Capillary electrophoresis-integrated immobilized enzyme microreactor with graphene oxide as support: Immobilization of negatively charged L-lactate dehydrogenase via hydrophobic interactions

We report the first application of hydrophobic interaction between graphene oxide (GO) and negatively charged enzymes to fabricate CE-integrated immobilized enzyme microreactors (IMERs) by a simple and reliable immobilization procedure based on layer by layer assembly. L-lactate dehydrogenase (L-LDH), which is negatively charged during the enzymatic reaction, is selected as the model enzyme. Various spectroscopic techniques, including SEM, FTIR, and UV-vis are used to characterize the fabricated CE-IMERs, demonstrating the successful immobilization of enzymes on the negatively charged GO layer in the capillary surface. The IMER exhibits excellent repeatability with RSDs of inter-day and batch-to-batch less than 3.49 and 6.37%, respectively, and the activity of immobilized enzymes remains about 90% after five-day usage. The measured K_m values of pyruvate and NADH of the immobilized L-LDH are in good agreement with those obtained by free enzymes. The results demonstrate that the hydrophobic interactions and/or π-π stacking is significant between the GO backbone and the aromatic residues of L-LDH and favorable to fabrication of CE-integrated IMERs. Finally, the method is successfully applied to the determination of pyruvate in beer samples.

Non-covalent assembled laccase-graphene composite: Property, stability and performance in beta-blocker removal

Immobilization of enzymes on carriers have been pursued to make the enzyme stable, reusable and obtaining even better enzyme activity. Due to the highly stable two-dimensional layer structure, large surface area and pore volume, graphene materials were seemed as ideal carrier for enzyme immobilization. In this paper, pristine few layer graphene (FLG) was applied to interact with laccase to synthesize laccase-graphene composite and the results of AFM, FT-IR and adsorption isotherm suggested that laccase was loaded on the FLG with a very high loading dosage (221.1 mg g^-1). Based on the measured interaction force and binding type between laccase and graphene, we proposed that the great enzyme loading on FLG is likely due to the non-covalent π-π stacking in addition to the large surface area of FLG. The composite has better stability to the variance of pH and storage temperature than free laccase. The synthesized composite can effectively transform beta-blocker labetalol with an enhanced efficiency, though the possible reaction pathways kept not changing. We further performed molecular simulation study on the crystal structure variation of laccase binding on FLG and proposed that catalytic activity enhancement may be attributed to the more exposure extent of the catalytic center of laccase. In addition, the laccase-graphene composite can be reused more than ten times in catalyzing the labetalol removal.

A sintered graphene/titania material as a synthetic keratoprosthesis skirt for end-stage corneal disorders

An artificial cornea or keratoprosthesis requires high mechanical strength, good biocompatibility, and sufficient wear and corrosion resistance to withstand the hostile environment. We report a reduced graphene oxide-reinforced titania-based composite for this application. Graphene oxide nanoparticles (GO) and liquid crystalline graphene oxide (LCGO) were the graphene precursors and mixed with titanium dioxide (TiO₂) powder. The composites reinforced with reduced GO or LCGO were produced through spark plasma sintering (SPS). The mechanical properties (Young's modulus and hardness), wear behaviour and corrosion resistance were studied using nanoindentation, anoidic polarization, long-term corrosion assay in artificial tear fluid and tribology assay in corroboration with atomic force microscopy and scanning electron microscopy. Biocompatibility was assessed by human corneal stromal cell attachment, survival and proliferation, and DNA damages. Sintered composites were implanted into rabbit corneas to assess for in vivo stability and host tissue responses. We showed that reduced graphene/TiO₂ hybrids were safe and biocompatible. In particular, the 1% reduced LCGO/TiO₂ (1rLCGO/TiO₂) composite was mechanically strong, chemically stable, and showed better wear and corrosion resistance than pure titania and other combinations of graphene-reinforced titania. Hence the 1rLCGO/ TiO₂ bioceramics can be a potential skirt biomaterial for keratoprosthesis to treat end-stage corneal blindness. STATEMENT OF SIGNIFICANCE: The osteo-odonto-keratoprosthesis (OOKP) is an artificial cornea procedure used to restore vision in end-stage corneal diseases, however it is contraindicated in young subjects, patients with advanced imflammatory diseases and posterior segment complications. Hence, there is a need of an improved keratoprosthesisskirt material with high mechanical and chemical stability, wear resistance and tissue integration ability. Our study characterized a reduced graphene oxide-reinforced titania-based biomaterial, which demonstrated strong mechanical strength, wear and corrosion resistance, and was safe and biocompatible to human corneal stromal cells. In vivo implantation to rabbit corneas did not cause any immune and inflammation outcomes. In conclusion, this invention is a potential keratoprosthesis skirt biomaterial to withstand the hostile environment in treating end-stage corneal blindness.

Molecular interactions of MnO2@RGO (manganese dioxide-reduced graphene oxide) nanocomposites with bovine serum albumin

Graphene based materials have attracted global attention due to their excellent properties. GO-metal oxide nanocomposites have been conjugated with biomolecules for the development of novel materials and potentially used as biomarkers. Herein, a detailed study on the interaction of Bovine serum albumin (BSA) with MnO₂@RGO (manganese dioxide-reduced graphene oxide) nanocomposites (NC) has been carried out. MnO₂@RGO nanocomposites were prepared through a template/surfactant free hydrothermal route at 180 °C for 12 h by varying the graphene oxide (GO) concentration. Different biophysical experiments have been carried out to evaluate molecular interactions between BSA and NCs. Intrinsic fluorescence has been used to quantify the quenching efficiency of NCs and the binding association of BSA-NC complexes. NCs effectively quenched the intrinsic fluorescence of BSA via static and dynamic mechanism. Further, the results indicate that the molecular interactions of NC with BSA are dependent on the GO percentage in NC. Circular dichroism results demonstrate nominal changes in the secondary structure of BSA in presence of NCs. Also, the esterase-like activity of BSA was marginally affected after adsorption upon NCs. In addition, the FESEM micrographs reveal that the protein-NC complexes consist of nanorod and sheet-like morphologies are forming aggregates of different sizes. We hope that this study will provide a basis for the design of novel graphene based and other related nanomaterials for several biological applications.Communicated by Ramaswamy H. Sarma.

Direct growth of few-layer graphene on AlN-based resonators for high-sensitivity gravimetric biosensors

We present the successful growth of few-layer graphene on top of AlN-based solidly mounted resonators (SMR) using a low-temperature chemical vapour deposition (CVD) process assisted by Ni catalysts, and its effective bio-functionalization with antibodies. The SMRs are manufactured on top of fully insulating AlN/SiO2 acoustic mirrors able to withstand the temperatures reached during the CVD growth of graphene (up to 650 °C). The active AlN films, purposely grown with the c-axis tilted, effectively excite shear modes displaying excellent in-liquid performance, with electromechanical coupling and quality factors of around 3% and 150, respectively, which barely vary after graphene integration. Raman spectra reveal that the as-grown graphene is composed of less than five weakly coupled layers with a low density of defects. Two functionalization protocols of the graphene are proposed. The first one, based on a covalent binding approach, starts with a low-damage O2 plasma treatment that introduces a controlled density of defects in graphene, including carboxylic groups. After that, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry is used to covalently bind streptavidin molecules to the surface of the sensors. The second functionalization protocol is based on the non-covalent bonding of streptavidin on hydrophobic graphene surfaces. The two protocols end with the effective bonding of biotinylated anti-IgG antibodies to the streptavidin, which leaves the surface of the devices ready for possible IgG detection.

Preparation, Mechanical Properties, and Biocompatibility of Graphene Oxide-Reinforced Chitin Monofilament Absorbable Surgical Sutures

Chitin (CT) is a good material to prepare surgical sutures due to its conspicuous biological characteristics. However, the poor mechanical strength of pure CT sutures limits its application. In order to improve its strength, a composite monofilament absorbable suture was prepared in this study using graphene oxide and chitin (GO-CT) using a green method. FT-IR spectra showed that GO-CT contained the characteristic functional groups of GO and CT, indicating that a GO-CT suture was successfully obtained. With the addition of a small amount of GO (1.6wt% solution) in chitin, the breaking tensile strength, knot strength, and knot-pull strength of the GO-CT suture were significantly improved compared to the CT suture. The biocompatibility of the GO-CT suture in vitro was checked by tetrazolium-based colorimetric assays and no cytotoxicity to L929 cells was found. In vivo, the subcutaneous implantation of GO-CT sutures in the dorsal skin of rats found no abnormalities by hematoxylin-eosin staining. Furthermore, there were no significant changes in the gene expression of the inflammatory mediators, interleukin 1β (IL-1β), tumor necrosis factor-α, IL-6, IL-17A, interferon-γ, or IL-10; however, the expression of transforming growth factor β was significantly increased in the first week. In summary, GO-CT sutures may have potential as a suture material in the clinic.

Transport and retention of reduced graphene oxide materials in saturated porous media: Synergistic effects of enhanced attachment and particle aggregation

The increasing production and use of graphene-based nanomaterials (e.g., graphene oxide (GO) and reduced graphene oxide (RGO)) will lead to their environmental release. To date, transport of RGOs in saturated porous media is poorly understood. Here, we examined the transport behaviors of three RGO materials obtained by reducing a GO product with commonly used reducing agents - N₂H₄, NaBH₄ and L-ascorbic acid (referred to as N₂H₄-RGO, NaBH₄-RGO and VC-RGO, respectively). When the dominant background cation was Na⁺, K⁺ or Mg²⁺, the mobility of the RGOs and GO in saturated quartz sand correlated well with their surface C/O ratio. Interestingly, the lower mobility of the more reduced materials (the ones with higher C/O values) was not only the results of their less negative surface charges and larger particle sizes, but also the outcome of their greater hydrophobicity, in line with the calculated extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) profiles. Counterintuitively, when the background cation was Ca²⁺, the least reduced material among the three RGOs, VC-RGO, exhibited the lowest mobility. Analysis of electrophoretic and aggregation properties, as well as pH-effect experiments, indicated that the surprisingly low mobility of VC-RGO was attributable to the strong cation-bridging effect (primarily Ca²⁺-bridging between RGO and quartz sand) associated with this material, as VC-RGO contained the highest amount of surface carboxyl group (a strong metal-binding moiety). Notably, enhanced attachment (due to increased hydrophobic effect and cation-bridging) and particle aggregation appeared to work synergistically to increase RGO retention, as the attachment of large RGO aggregates significantly enhanced particle straining by narrowing the flow path. These observations reveal a largely overlooked link between the mobility of graphene-based materials and their key physicochemical properties.