Modulating aβ33-42 peptide assembly by graphene oxide

Enhancing anti-amyloidogenic properties and antioxidant effects of Scutellaria baicalensis polyphenols through novel nanoparticle formation

Protein aggregation and oxidative stress have gained significant research attention due to their association with a group of diseases known as amyloidosis. Among the strategies developed to prevent amyloidosis, utilization of polyphenols stands out as one of the most commonly employed approaches. Scutellaria baicalensis is renowned as one of the foremost herbal sources of polyphenols. In this study, we employed a direct oxidative pyrolysis method for polymerizing S. baicalensis's polyphenols (SBPPs) after their extraction, resulting in the formation of novel SBPPs nanoparticles. Upon polymerization, SBPPs nanoparticles showed remarkable properties including heightened water solubility, increased surface area, modified surface functional groups, and enhanced stability. As a result of these diverse factors, there was a considerable enhancement in the anti-amyloidogenic properties and antioxidant effects of SBPPs nanoparticles compared to its bulk form. The fibrillation kinetics, AFM images, and cytotoxicity assays strongly indicate that SBPPs nanoparticles are more effective than SBPPs at preventing amyloid fibril formation and associated cell toxicity. Additionally, SBPPs nanoparticles demonstrated more effective prevention of reactive oxygen species (ROS) production. In conclusion, the use of SBPPs in nanoparticle form presents a promising strategy to enhance anti-amyloidogenic properties, mitigate oxidative stress, and offer potential therapeutic benefits for amyloidosis-related diseases.

Cooperative dissolution of peptidomimetic vesicles and amyloid β fibrils

The aggregation of amyloid proteins in the brain is a significant neurotoxic event that contributes to neurodegenerative disorders. The aggregation of amyloid beta (Aβ), particularly Aβ42 monomers, into various forms such as oligomers, protofibrils, fibrils, and amyloid plaques is a key pathological feature in Alzheimer's disease. As a result, Aβ42 is a primary target and the development of molecular strategies for the dissolution of Aβ42 aggregates is considered a promising approach to mitigating Alzheimer's disease pathology. A set of pyrene-conjugated peptidomimetics derived from Aβ14-23 (AkdcPy, AkdmPy, and AkdnPy) by incorporating an unnatural amino acid [kd: cyclo(Lys-Asp)] were studied for their ability to modulate Aβ42 aggregation. AkdcPy and AkdmPy formed vesicular structures in aqueous media. The vesicles of AkdmPy loaded with the neuroprotective compound berberine (Ber), dissipated mutually in the presence of preformed Aβ42 fibrils. During this process, the active drug Ber was released. This work is expected to inspire the development of drug-loaded peptidomimetic-based therapeutic formulations to modulate disorders associated with amyloid toxicity.

Nanotechnology-enhanced fiber-reinforced polymer composites: Recent advancements on processing techniques and applications

Incorporating nanoparticles can significantly improve the performance and functionality of fiber-reinforced polymer (FRP) composites. Different techniques exist for processing, testing, and implementing nanocomposites in various industries. Depending on these factors, these materials can be tailored to suit the specific applications of the automotive and aerospace industries, defence industries, biomedical and energy sectors etc. Nanotechnology offers several potential benefits for composites, including improved mechanical properties, surface modification, and sensing capabilities. This paper discusses the different types of nanoparticles, nanofibers, and nano-coating that can be used for reinforcement, surface modification, and property enhancement in FRP composites. It also examines the challenges associated with incorporating nanotechnology into composites and provides recommendations for potential opportunities in future work. This study is intended to offer a comprehensive understanding of the current research on using nanotechnology in FRP composites and its potential impact on the composites industry.

Detection and modulation of neurodegenerative processes using graphene-based nanomaterials: Nanoarchitectonics and applications

Neurodegenerative disorders (NDDs) are caused by progressive loss of functional neurons following the aggregation and fibrillation of proteins in the central nervous system. The incidence rate continues to rise alarmingly worldwide, particularly in aged population, and the success of treatment remains limited to symptomatic relief. Graphene nanomaterials (GNs) have attracted immense interest on the account of their unique physicochemical and optoelectronic properties. The research over the past two decades has recognized their ability to interact with aggregation-prone neuronal proteins, regulate autophagy and modulate the electrophysiology of neuronal cells. Graphene can prevent the formation of higher order protein aggregates and facilitate the clearance of such deposits. In this review, after highlighting the role of protein fibrillation in neurodegeneration, we have discussed how GN-protein interactions can be exploited for preventing neurodegeneration. A comprehensive understanding of such interactions would contribute to the exploration of novel modalities for controlling neurodegenerative processes.

Advanced nanomaterials for modulating Alzheimer's related amyloid aggregation

Alzheimer's disease (AD) is a common neurodegenerative disease that brings about enormous economic pressure to families and society. Inhibiting abnormal aggregation of Aβ and accelerating the dissociation of aggregates is treated as an effective method to prevent and treat AD. Recently, nanomaterials have been applied in AD treatment due to their excellent physicochemical properties and drug activity. As a drug delivery platform or inhibitor, various excellent nanomaterials have exhibited potential in inhibiting Aβ fibrillation, disaggregating, and clearing mature amyloid plaques by enhancing the performance of drugs. This review comprehensively summarizes the advantages and disadvantages of nanomaterials in modulating amyloid aggregation and AD treatment. The design of various functional nanomaterials is discussed, and the strategies for improved properties toward AD treatment are analyzed. Finally, the challenges faced by nanomaterials with different dimensions in AD-related amyloid aggregate modulation are expounded, and the prospects of nanomaterials are proposed.

Nontoxic silicene photothermal agents with high near-infrared absorption for disassembly of Alzheimer's amyloid‑β fibrils

The disassembly and eliminating the amyloid-β (Aβ) aggregates has become an effective way to treat Alzheimer's disease (AD). Herein, for the first time, the near-infrared (NIR) activated silicene nanosheets (SNSs) have been identified as an effective nontoxic photothermal conversion agent for irreversibly disassembly of the Aβ_33-42 aggregates. The SNSs synthesized by a combination of mild oxidation method and liquid exfoliation method possess good biocompatibility and biodegradability, and high near-infrared photothermal conversion capabilities. Under NIR light, the SNSs could disassemble the large and dense Aβ_33-42 mature fibrils into short fibrils and even form thin films, leading to the degradation rate of 96.47%. The circular dichroism spectrum, fluorescent spectra, and nanostructure were analyzed to monitor the photothermal degradation of mature Aβ_33-42 fibrils for elaborating the mechanism beneath. This study might provide a clue for developing potential therapeutic strategy for AD and related neurodegenerative diseases.

Design of Peptides that Fold and Self-Assemble on Graphite

The graphite-water interface provides a unique environment for polypeptides that generally favors ordered structures more than in solution. Therefore, systems consisting of designed peptides and graphitic carbon might serve as a convenient medium for controlled self-assembly of functional materials. Here, we computationally designed cyclic peptides that spontaneously fold into a β-sheet-like conformation at the graphite-water interface and self-assemble, and we subsequently observed evidence of such assembly by atomic force microscopy. Using a novel protocol, we screened nearly 2000 sequences, optimizing for formation of a unique folded conformation while discouraging unfolded or misfolded conformations. A head-to-tail cyclic peptide with the sequence GTGSGTGGPGGGCGTGTGSGPG showed the greatest apparent propensity to fold spontaneously, and this optimized sequence was selected for larger scale molecular dynamics simulations, rigorous free-energy calculations, and experimental validation. In simulations ranging from hundreds of nanoseconds to a few microseconds, we observed spontaneous folding of this peptide at the graphite-water interface under many different conditions, including multiple temperatures (295 and 370 K), with different initial orientations relative to the graphite surface, and using different molecular dynamics force fields (CHARMM and Amber). The thermodynamic stability of the folded conformation on graphite over a range of temperatures was verified by replica-exchange simulations and free-energy calculations. On the other hand, in free solution, the folded conformation was found to be unstable, unfolding in tens of picoseconds. Intermolecular hydrogen bonds promoted self-assembly of the folded peptides into linear arrangements where the peptide backbone exhibited a tendency to align along one of the six zigzag directions of the graphite basal plane. For the optimized peptide, atomic force microscopy revealed growth of single-molecule-thick linear patterns of 6-fold symmetry, consistent with the simulations, while no such patterns were observed for a control peptide with the same amino acid composition but a scrambled sequence.

Nanomaterials for Modulating the Aggregation of β-Amyloid Peptides

The aberrant aggregation of amyloid-β (Aβ) peptides in the brain has been recognized as the major hallmark of Alzheimer's disease (AD). Thus, the inhibition and dissociation of Aβ aggregation are believed to be effective therapeutic strategiesforthe prevention and treatment of AD. When integrated with traditional agents and biomolecules, nanomaterials can overcome their intrinsic shortcomings and boost their efficiency via synergistic effects. This article provides an overview of recent efforts to utilize nanomaterials with superior properties to propose effective platforms for AD treatment. The underlying mechanismsthat are involved in modulating Aβ aggregation are discussed. The summary of nanomaterials-based modulation of Aβ aggregation may help researchers to understand the critical roles in therapeutic agents and provide new insight into the exploration of more promising anti-amyloid agents and tactics in AD theranostics.

Amyloid Oligomers: A Joint Experimental/Computational Perspective on Alzheimer's Disease, Parkinson's Disease, Type II Diabetes, and Amyotrophic Lateral Sclerosis

Protein misfolding and aggregation is observed in many amyloidogenic diseases affecting either the central nervous system or a variety of peripheral tissues. Structural and dynamic characterization of all species along the pathways from monomers to fibrils is challenging by experimental and computational means because they involve intrinsically disordered proteins in most diseases. Yet understanding how amyloid species become toxic is the challenge in developing a treatment for these diseases. Here we review what computer, in vitro, in vivo, and pharmacological experiments tell us about the accumulation and deposition of the oligomers of the (Aβ, tau), α-synuclein, IAPP, and superoxide dismutase 1 proteins, which have been the mainstream concept underlying Alzheimer's disease (AD), Parkinson's disease (PD), type II diabetes (T2D), and amyotrophic lateral sclerosis (ALS) research, respectively, for many years.

Isomeric Effect of Nano-Inhibitors on Aβ40 Fibrillation at The Nano-Bio Interface

Chemical and physical properties of nanobio interface substantially affect the conformational transitions of adjacent biomolecules. Previous studies have reported the chiral effect and charge effect of nanobio interface on the misfolding, aggregation, and fibrillation of amyloid protein. However, the isomeric effect of nanobio interface on protein/peptides amyloidosis is still unclear. Here, three isomeric nanobio interfaces were designed and fabricated based on the same sized gold nanoclusters (AuNCs) modified with 4-mercaptobenzoic acid (p-MBA), 3-mercaptobenzoic acid (m-MBA), and 2-mercaptobenzoic acid (o-MBA). Then three isomeric AuNCs were employed as models to explore the isomeric effect on the misfolding, aggregation, and fibrillation of Aβ₄₀ at nanobio interfaces. Site-specific replacement experiments on the basis of theoretical analysis revealed the possible mechanism of Aβ₄₀ interacting with isomeric ligands of AuNCs at the nanobio interfaces. The distance and orientation of -COOH group from the surface of AuNCs can affect the electrostatic interaction between isomeric ligands and the positively charged residues (R5, K16, and K28) of Aβ₄₀, which may affect the inhibition efficiency of isomeric AuNCs on protein amyloidosis. Actually, the amyloid fibrillation kinetics results together with atomic force microscope (AFM) images, dynamic light scattering (DLS) results and circular dichroism (CD) spectra indeed proved that all the three isomeric AuNCs could inhibit the misfolding, aggregation and fibrillation of Aβ₄₀ in a dose-dependent manner, and the inhibition efficiency was definitely different from each other. The inhibition efficiency of o-MBA-AuNCs was higher than that of m-MBA-AuNCs and p-MBA-AuNCs at the same dosage. These results provide an insight for isomeric effect at nanobio interfaces, and open an avenue for structure-based nanodrug design target Alzheimer's disease (AD) and even other protein conformational diseases.

Biomembrane induced in situ self-assembly of peptide with enhanced antimicrobial activity

Antimicrobial peptides (AMPs) as biocides are of great interest because they have the ability to combat antibiotic resistance. Normally, natural AMPs need to be rationally designed or modified for practical use as an antibiotic. Here, a novel AMP, termed FF8, which is a cationic octapeptide composed of arginine, lysine, and phenylalanine, was designed. The FF8 was found to self-assemble into nanofibers when induced by a negatively charged lipid membrane or pH is above 9.4. The fibers on the membrane broke the lipid membrane, forming pores and significantly reducing its fluidity. FF8 also exhibited enhanced antibacterial activity by significantly increasing the permeability of the inner and outer membranes of Escherichia coli (E. coli) and maintaining the pores of the inner membrane of cells, which caused continuous membrane leakage. Because of its high antibacterial activity, cytocompatibility, and cost-effectiveness, FF8 is a promising antibacterial material.

Self-Assembly of Ferrocene-Phenylalanine@Graphene Oxide Hybrid Hydrogels for Dopamine Detection

The effect of graphene oxide (GO) is explored on the self-assembly behavior of ferrocene-L-phenylalanine (Fc-F) in solution. The assembly behavior of Fc-F in GO dispersions at different concentrations and pH values was systematically investigated. At pH 8, a stable hybrid material could be formed by facile and elaborate supramolecular assembly. Moreover, the concentration of GO could also be used to adjust the mechanical strength of the hybrid hydrogel. Increasing the concentration of GO in the assembly process, a hydrogel with better mechanical strength could be obtained. The storage modulus could be up to 6.3 kPa by increasing the GO concentration to 1 mg/mL. Finally, the dopamine concentration in the solution could be detected in a high accuracy by loading the hybrid hydrogel onto the electrode surface. The R² of linear fitting equation could reach 0.9915 in the range of 10-200 μmol/L, indicating that it has the potential as biosensing electrode material.

Graphene oxide sheets and quantum dots inhibit α-synuclein amyloid formation by different mechanisms

Aggregation and amyloid formation of the 140-residue presynaptic and intrinsically disordered protein α-synuclein (α-syn) is a pathological hallmark of Parkinson's disease (PD). Understanding how α-syn forms amyloid fibrils, and investigations of agents that can prevent their formation is therefore important. We demonstrate herein that two types of graphene oxide nanoparticles (sheets and quantum dots) inhibit α-syn amyloid formation by different mechanisms mediated via differential interactions with both monomers and fibrils. We have used thioflavin-T fluorescence assays and kinetic analysis, circular dichroism, dynamic light scattering, fluorescence spectroscopy and atomic force microscopy to asses the kinetic nature and efficiency of this inhibitory effect. We show that the two types of graphene oxide nanoparticles alter the morphology of α-syn fibrils, disrupting their interfilament assembly and the resulting aggregates therefore consist of single protofilaments. Our results further show that graphene oxide sheets reduce the aggregation rate of α-syn primarily by sequestering of monomers, thereby preventing primary nucleation and elongation. Graphene quantum dots, on the other hand, interact less avidly with both monomers and fibrils. Their aggregation inhibitory effect is primarily related to adsorption of aggregated species and reduction of secondary processes, and they can thus not fully prevent aggregation. This fine-tuned and differential effect of graphene nanoparticles on amyloid formation shows that rational design of these nanomaterials has great potential in engineering materials that interact with specific molecular events in the amyloid fibril formation process. The findings also provide new insight into the molecular interplay between amyloidogenic proteins and graphene-based nanomaterials in general, and opens up their potential use as agents to manipulate fibril formation.

Identification and Nanomechanical Characterization of the HIV Tat-Amyloid β Peptide Multifibrillar Structures

HIV transactivator of transcription (Tat) protein could interact with amyloid β (Aβ) peptide which cause the growth of Aβ plaques in the brain and result in Alzheimer's disease in HIV-infected patients. Herein, we employ high-resolution atomic force microscopy and quantitative nanomechanical mapping to investigate the effects of Tat protein in Aβ peptide aggregation. Our results demonstrate that the Tat protein could bind to the Aβ fibril surfaces and result in the formation of Tat-Aβ multifibrillar structures. The resultant Tat-Aβ multifibrillar aggregates represent an increase in stiffness compared with Aβ fibrils due to the increase in β-sheet formation. The identification and characterization of the Tat-Aβ intermediate aggregates is important to understanding the interactions between Tat protein and Aβ peptide, and the development of novel therapeutic strategy for Alzheimer's disease-like disorder in HIV infected individuals.

Revisiting thioflavin T (ThT) fluorescence as a marker of protein fibrillation - The prominent role of electrostatic interactions

Thioflavin T (ThT), a benzothiazole-based fluorophore, is a prominent dye widely employed for monitoring amyloid fibril assembly. Despite the near-universal presumption that ThT binds to β-sheet domains upon fibrillar surface via hydrophobic forces, the contribution of the positive charge of ThT to fibril binding and concomitant fluorescence enhancement have not been thoroughly assessed. Here we demonstrate a considerable interdependence between ThT fluorescence and electrostatic charges of peptide fibrils. Specifically, by analyzing both fibril-forming synthetic peptides and prominent natural fibrillar peptides, we demonstrate pronounced modulations of ThT fluorescence signal that were solely dependent upon electrostatic interactions between ThT and peptide surface. The results further attest to the fact that fibril ζ-potential rather than pH-dependent assembly of the fibrils constitute the primary factor affecting ThT binding and fluorescence. This study provides the first quantitative assessment of electrostatically driven ThT fluorescence upon adsorption to amyloid fibrils.

Protein-Carbon Dot Nanohybrid-Based Early Blood-Brain Barrier Damage Theranostics

For effective treatment of ischemic cerebral thrombosis, it is of great significance to find a facile way in assessing the early damage of blood-brain barrier (BBB) after ischemic stroke during thrombolysis by integrating thrombolytic agents with fluorescent materials. Herein, a novel type of protein-carbon dot  nanohybrids is reported by the incorporation of carbon dots on thrombolytic agents through covalent linkage. Both in vitro and ex vivo fluorescence imaging measurements have demonstrated remarkable imaging effects in the brain of transient middle cerebral artery occlusion mice. Besides, the outstanding thrombolytic capacity of the nanohybrids was determined by in vitro thrombolysis tests. As one of the few reports of the construction of thrombolytic agents and fluorescent nanomaterials, the nanohybrids retain thrombolysis ability and fluorescent traceability simultaneously. It may provide a promising indicator for early BBB damage and thrombolytic agent distribution to estimate the possibility of symptomatic intracranial hemorrhage after thrombolysis and supply tissue window evidence for clinical thrombolytic agent application.

Role of surface oxygen-containing functional groups of graphene oxide quantum dots on amyloid fibrillation of two model proteins

There are many reports demonstrating that various derivatives of carbon nanoparticles are effective inhibitors of protein aggregation. As surface structural features of nanoparticles play a key role on modulating amyloid fibrillation process, in the present in vitro study, bovine insulin and hen egg white lysozyme (HEWL) were selected as two model proteins to investigate the reducing effect of graphene oxide quantum dots (GOQDs) on their assembly under amyloidogenic conditions. GOQDs were prepared through direct pyrolysis of citric acid, and the reduction step was carried out using ascorbic acid. The prepared nanoparticles were characterized by UV-Vis, X-ray photoelectron, and FT-IR spectroscopies, transmission electron and atomic force microscopies, zeta potential measurement, and Nile red fluorescence assay. They showed the tendencies to modulate the assembly of the proteins through different mechanisms. While GOQDs appeared to have the capacity to inhibit fibrillation, the presence of reduced GOQDs (rGOQDs) was found to promote protein assembly via shortening the nucleation phase, as suggested by ThT fluorescence data. Moreover, the structures produced in the presence of GOQDs or rGOQDs were totally nontoxic. We suggest that surface properties of these particles may be part of the differences in their mechanism(s) of action.

Photodegradation of porphyrin-bound hIAPP(1–37) fibrils

Amyloid deposits in pancreatic islets of type 2 diabetes mellitus (T2DM) are mainly comprised of human islet amyloid polypeptide (hIAPP), the degradation of hIAPP fibrils by photoactive porphyrin could be a preventive strategy against T2DM.

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.

Unconventional Atomic Structure of Graphene Sheets on Solid Substrates

The atomic structure of free-standing graphene comprises flat hexagonal rings with a 2.5 Å period, which is conventionally considered the only atomic period and determines the unique properties of graphene. Here, an unexpected highly ordered orthorhombic structure of graphene is directly observed with a lattice constant of ≈5 Å, spontaneously formed on various substrates. First-principles computations show that this unconventional structure can be attributed to the dipole between the graphene surface and substrates, which produces an interfacial electric field and induces atomic rearrangement on the graphene surface. Further, the formation of the orthorhombic structure can be controlled by an artificially generated interfacial electric field. Importantly, the 5 Å crystal can be manipulated and transformed in a continuous and reversible manner. Notably, the orthorhombic lattice can control the epitaxial self-assembly of amyloids. The findings reveal new insights about the atomic structure of graphene, and open up new avenues to manipulate graphene lattices.

Effect of extract from ginseng rust rot on the inhibition of human hepatocellular carcinoma cells in vitro

Hepatocellular carcinoma (HCC) is one of major leading causes of cancer death worldwide. As a traditional medicine, the anti-cancer function of ginseng is being growingly recognized and investigated. However, the effect of ginseng rust rot on human HCC is unknown yet. In this study, the HCC cells were treated with different parts of mountain cultivated ginseng rust rot and compared with human normal liver cells. The morphology, survival rate and β-actin expression of the cells were changed by introducing the ginseng epidermis during the incubation process. Notably, the results reveal that the ginseng epidermis can induce apoptosis by altering the morphologies of cells, indicating the practical implication for the HCC treatment and drug development.

Multifunctional inhibitors of β-amyloid aggregation based on MoS2/AuNR nanocomposites with high near-infrared absorption

Recent advances in nanotechnology have developed a lot of opportunities for biological applications. In this work, multifunctional MoS2/AuNR nanocomposites with unique high NIR absorption were designed via combining MoS2 nanosheets and gold nanorods (AuNRs). The nanocomposites were synthesized through electrostatic self-assembly and showed high stability and good biocompatibility. Then they were used to modulate the aggregation of amyloid-β peptides, destabilize mature fibrils under NIR irradiation, and eliminate Aβ-induced ROS against neurotoxicity. The inhibition and destabilization effects were confirmed by Thioflavin T (ThT) fluorescence assay and transmission electron microscopy (TEM). Cell viability assay and ROS assay revealed that MoS2/AuNR nanocomposites could alleviate Aβ-induced oxidative stress and cell toxicity. More importantly, both MoS2 nanosheets and AuNRs can be used as NIR photothermal agents, MoS2/AuNR nanocomposites have enhanced ability of disrupting Aβ fibrils and improved cell viability by generating local heat under low power NIR irradiation. Our results provide new insights into the design of new multifunctional systems for the treatment of amyloid-related diseases.

Electric Field-Induced Chemical Surface-Enhanced Raman Spectroscopy Enhancement from Aligned Peptide Nanotube-Graphene Oxide Templates for Universal Trace Detection of Biomolecules

Semiconductor-graphene oxide-based surface-enhanced Raman spectroscopy substrates represent a new frontier in the field of surface-enhanced Raman spectroscopy (SERS). However, the application of graphene oxide has had limited success because of the poor Raman enhancement factors that are achievable in comparison to noble metals. In this work, we report chemical SERS enhancement enabled by the application of an electric field (10-25 V/mm) to aligned semiconducting peptide nanotube-graphene oxide composite structures during Raman measurements. The technique enables nanomolar detection sensitivity of glucose and nucleobases with up to 10-fold signal enhancement compared to metal-based substrates, which, to our knowledge, is higher than that previously reported for semiconductor-based SERS substrates. The increased Raman scattering is assigned to enhanced charge-transfer resonance enabled by work function lowering of the peptide nanotubes. These results provide insight into how semiconductor organic peptide nanotubes interact with graphene oxide, which may facilitate chemical biosensing, electronic devices, and energy-harvesting applications.

Controlling the Self-Assembly of Biomolecules into Functional Nanomaterials through Internal Interactions and External Stimulations: A Review

Biomolecular self-assembly provides a facile way to synthesize functional nanomaterials. Due to the unique structure and functions of biomolecules, the created biological nanomaterials via biomolecular self-assembly have a wide range of applications, from materials science to biomedical engineering, tissue engineering, nanotechnology, and analytical science. In this review, we present recent advances in the synthesis of biological nanomaterials by controlling the biomolecular self-assembly from adjusting internal interactions and external stimulations. The self-assembly mechanisms of biomolecules (DNA, protein, peptide, virus, enzyme, metabolites, lipid, cholesterol, and others) related to various internal interactions, including hydrogen bonds, electrostatic interactions, hydrophobic interactions, π⁻π stacking, DNA base pairing, and ligand⁻receptor binding, are discussed by analyzing some recent studies. In addition, some strategies for promoting biomolecular self-assembly via external stimulations, such as adjusting the solution conditions (pH, temperature, ionic strength), adding organics, nanoparticles, or enzymes, and applying external light stimulation to the self-assembly systems, are demonstrated. We hope that this overview will be helpful for readers to understand the self-assembly mechanisms and strategies of biomolecules and to design and develop new biological nanostructures or nanomaterials for desired applications.

Observations of Gradual Chiral Self-Recognition of Adsorbed Aromatic Compound

The self-assembly of two-dimensional chiral 1 H,5 H-benzo(1,2- d:4,5- d')bistriazole (H₂bbta) on a Ag(110) surface was investigated by ultra-high-vacuum scanning tunneling microscopy. The gradual formation of ordered structures by H₂bbta molecules with the same chirality recognizing each other was observed as the annealing temperature was increased from 300 to 333 K. When the sample was annealed at 355 K, the homochiral structures were converted to coexisting structures containing λ-H₂bbta and δ-H₂bbta in a ratio of 6:1. Density functional theory (DFT) calculations revealed that thermally driven and intermolecular interactions induced chiral self-recognition to form enantiomorphous H₂bbta structures in which N-H···N hydrogen bonds and C-H···N hydrogen bonds are the main attractive forces.

Enhanced Photoresponsive Graphene Oxide-Modified g-C3N4 for Disassembly of Amyloid β Fibrils

Protein misfolding and abnormal self-assembly lead to the aggregates of oligomers, fibrils, or senior amyloid β (Aβ) plaques, which are associated with the pathogenesis of many neurodegenerative diseases. Progressive cerebral accumulation of Aβ protein was widely proposed to explain the cause of Alzheimer's disease, for which one promising direction of the preclinical study is to convert the preformed β-sheet structure of Aβ aggregates into innocent structures. However, the conversion is even harder than the modulation of the amyloidosis process. Herein, a graphene oxide/carbon nitride composite was developed as a good photocatalyst for irreversibly disassembling the Aβ aggregates of Aβ(33-42) under UV. Quartz crystal microbalance, circular dichroism spectrum, atomic force microscopy, fluorescent spectra, and mechanical property analysis were performed to analyze this photodegradation process from different aspects for fully understanding the mechanism, which may provide an important enlightenment for the relevant research in this field and neurodegenerative disease study.

Molecular dynamics simulations reveal the mechanism of graphene oxide nanosheet inhibition of Aβ1–42 peptide aggregation

Graphene oxide nanosheets inhibit Aβ1–42 aggregation by weakening inter-peptide interactions and reducing β-sheet contents mostly via salt bridge, hydrogen bonding and cation–π interactions with charged residues.

Photoinduced antibacterial activity of NRC03 peptide-conjugated dopamine/nano-reduced graphene oxide against Staphylococcus aureus

NRC03-DA/nRGO possessed biocompatible properties and NIR photothermal energy conversion capability. The continuous photoinduced NRC03 peptide release consequently improved the therapeutic efficiency of photothermal therapy against S. aureus.

Graphene Oxide Quantum Dot Alters Amyloidogenicity of Hen Egg White Lysozyme via Modulation of Protein Surface Character

A series of neurodegenerative disorders are caused by intracellular or extracellular amyloid deposition, including Alzheimer's disease, Parkinson's disease, Prion disease, and so on. To prevent the progress of such amyloid-mediated disorders, various agents have been tested including nanoparticles. Among different nanomaterials, graphene oxide shows unique electrochemical properties, which have potential applications in various biomedical fields. In our present investigation, we explored the effect of graphene oxide quantum dots (GOQDs) in amyloid β-fibrillation of hen egg white lysozyme (HEWL) under various conditions. Electron microscopy imaging showed that administration of GOQD inhibited HEWL amyloid β-fibrillation via producing thin and small fragments of fibrils. ζ-Potential measurement and 8-anilino-1-naphthalenesulfonic fluorescence study of lysozyme amyloid demonstrated a significant drop in surface hydrophobicity and an increase of surface charge of protein molecules. The reduced hydrophobic interaction and enhanced surface charge inhibit the hydrophobic assembly and colloidal stability of the protein. Circular dichroism and thioflavin-T fluorescence demonstrated that GOQD also interfered at the secondary structure level and prevented amyloid β-sheet formation and assembly of a protein by reducing the amount of amyloid β-sheet formation. Further, cellular toxicity analysis with HaCaT and 3T3 cells showed reduced toxicity of amyloid samples prepared with GOQD. Therefore, GOQD might be used to be a potential amyloid-preventive agent in various neurodegenerative diseases.

Directly probing the dissociation effects of graphene oxide nanosheets on hIAPP fibrils

The aggregation of human islet amyloid polypeptides (hIAPP) to mature fibrils is considered as the main cause of type II diabetes. Therefore destroying the pre-formed hIAPP fibrils is expected to be a promising strategy for therapeutic treatments. In this work, the dissociation effects of graphene oxide (GO) nanosheets on hIAPP mature fibrils are investigated. The results clearly demonstrate that hIAPP fibrils can be quickly adsorbed on the GO surface and efficiently broken into short fragments. Meanwhile, the β-sheet structures of hIAPP fibrils are greatly destroyed. Particularly, in situ atomic force microscopy was applied to monitor the real-time interaction between hIAPP fibrils and GO nanosheets. It provides distinct evidence that the disruption of hIAPP fibrils by GO nanosheets mainly occurs at the GO edges. Size-dependent experiments further justify the interfere of edge contribution, which suggest small-sized GO nanosheets exhibit better dissociation ability than large-sized ones. Therefore, this study not only provides valuable information that GO nanosheets (especially small-sized ones) can act as efficient nanoblades to break hIAPP fibrils, but also suggests a powerful and widely available methodology for investigating real-time interaction between nanomaterials and biomolecules.

Free Energy Landscape for Alpha-Helix to Beta-Sheet Interconversion in Small Amyloid Forming Peptide under Nanoconfinement

Understanding the mechanism of fibrillization of amyloid forming peptides could be useful for the development of therapeutics for Alzheimer's disease (AD). Taking this standpoint, we have explored in this work the free energy profile for the interconversion of monomeric and dimeric forms of amyloid forming peptides into different secondary structures namely beta-sheet, helix, and random coil in aqueous solution using umbrella sampling simulations and density functional theory calculations. We show that the helical structures of amyloid peptides can form β sheet rich aggregates through random coil conformations in aqueous condition. Recent experiments ( Chem. Eur. J. 2018, 24, 3397-3402 and ACS Appl. Mater. Interfaces 2017, 9, 21116-21123) show that molybdenum disulfide nanosurface and nanoparticles can reduce the fibrillization process of amyloid beta peptides. We have unravelled the free energy profile for the interconversion of helical forms of amyloid forming peptides into beta-sheet and random coil in the presence of a two-dimensional nanosurface of MoS₂. Results indicate that the monomer and dimeric forms of the peptides adopt the random coil conformation in the presence of MoS₂ while the helical form is preferable for the monomeric form and that the beta-sheet and helix forms are the preferable forms for dimers in aqueous solution. This is due to strong interaction with MoS₂ and intramolecular hydrogen bonds of random coil conformation. The stabilization of random coil conformation does not lead to a β sheet like secondary structure for the aggregate. Thus, the confinement of MoS₂ promotes deaggregation of amyloid beta peptides rather than aggregation, something that could be useful for the development of therapeutics for AD.

Effects of Size and Functionalization on the Structure and Properties of Graphene Oxide Nanoflakes: An in Silico Investigation

Graphitic nanoparticles, specifically, graphene oxide (GO) nanoflakes, are of major interest in the field of nanotechnology, with potential applications ranging from drug delivery systems to energy storage devices. These applications are possible largely because of the properties imparted by various functional groups attached to the GO surface by relatively simple production methods compared to pristine graphene. We investigated how varying the size and oxidation of GO flakes can affect their structural and dynamic properties in an aqueous solution. The all-atom modeling of the GO nanoflakes of different sizes suggested that the curvature and roughness of relatively small (3 × 3 nm) GO flakes are not affected by their degree of oxidation. However, the larger (7 × 7 nm) flakes exhibited an increase in surface roughness as their oxidation increased. The analysis of water structure around the graphitic nanoparticles revealed that the degree of oxidation does not affect the water dipole orientations past the first hydration layer. Nevertheless, oxygen functionalization induced a well-structured first hydration layer, which manifested in identifiable hydrophobic and hydrophilic patches on GO. The detailed all-atom models of GO nanoflakes will guide a rational design of functional graphitic nanoparticles for biomedical and industrial applications.

Graphene quantum dots prevent α-synucleinopathy in Parkinson's disease

Though emerging evidence indicates that the pathogenesis of Parkinson's disease is strongly correlated to the accumulation^1,2 and transmission^3,4 of α-synuclein (α-syn) aggregates in the midbrain, no anti-aggregation agents have been successful at treating the disease in the clinic. Here, we show that graphene quantum dots (GQDs) inhibit fibrillization of α-syn and interact directly with mature fibrils, triggering their disaggregation. Moreover, GQDs can rescue neuronal death and synaptic loss, reduce Lewy body and Lewy neurite formation, ameliorate mitochondrial dysfunctions, and prevent neuron-to-neuron transmission of α-syn pathology provoked by α-syn preformed fibrils^5,6. We observe, in vivo, that GQDs penetrate the blood-brain barrier and protect against dopamine neuron loss induced by α-syn preformed fibrils, Lewy body/Lewy neurite pathology and behavioural deficits.

Functional amyloid materials at surfaces/interfaces

With the development of nanotechnology, functional amyloid materials are drawing increasing attention, and numerous remarkable applications are emerging. Amyloids, defined as a class of supramolecular assemblies of misfolded proteins or peptides into β-sheet fibrils, have evolved in many new respects and offer abundant chemical/biological functions. These proteinaceous micro/nano-structures provide excellent biocompatibility, rich phase behaviours, strong mechanical properties, and stability at interfaces not only in nature but also in functional materials, displaying versatile interactions with surfaces/interfaces that have been widely adopted in bioadhesion, synthetic biology, and composites. Overall, functional amyloids at surfaces/interfaces have excellent potential applications in next-generation biotechnology and biomaterials.

Mechanistic insights into the inhibition and size effects of graphene oxide nanosheets on the aggregation of an amyloid-β peptide fragment

The aggregation of amyloid-β (Aβ), which involves the formation of small oligomers and mature fibrils, has received considerable attention in the past few decades due to its close link with Alzheimer's disease (AD). The inhibition of β-sheet formation has been considered as the primary therapeutic strategy for AD. In this respect, graphene oxide (GO) has gained significant attention because of its high solubility, good biocompatibility and inhibitory effect on the aggregation of Aβ and the 33-42 fragment (Aβ33-42). However, the inhibitory mechanism at the atomic level remains elusive. Herein, we investigated the oligomerization of Aβ33-42 by performing replica exchange molecular dynamics simulations on four Aβ33-42 peptide chains in the absence and presence of two different sizes of GO. Our simulations show that isolated Aβ33-42 can form fibril-prone extended β-sheets and barrel-like structures, whereas they are suppressed in the presence of GO nanosheets. Our data reveal that GO inhibits Aβ33-42 oligomerization by making Aβ33-42 peptides separate from each other through strong interactions with M35. With the same total number of atoms, GO120 displays better inhibitory effect than GO60 by providing a larger effective contact surface area. This study provides the molecular mechanism of GO in inhibiting the aggregation of Aβ33-42, which might offer a theoretical insight into the design of drugs against AD at the atomic level.

Kinetics of Surface-Mediated Fibrillization of Amyloid-β (12-28) Peptides

Surfaces or interfaces are considered to be key factors in facilitating the formation of amyloid fibrils under physiological conditions. In this report, we study the kinetics of the surface-mediated fibrillization (SMF) of an amyloid-β fragment (Aβ_12-28) on mica. We employ a spin-coating-based drying procedure to control the exposure time of the substrate to a low-concentration peptide solution and then monitor the fibril growth as a function of time via atomic force microscopy (AFM). The evolution of surface-mediated fibril growth is quantitatively characterized in terms of the length histogram of imaged fibrils and their surface concentration. A two-dimensional (2D) kinetic model is proposed to numerically simulate the length evolution of surface-mediated fibrils by assuming a diffusion-limited aggregation (DLA) process along with size-dependent rate constants. We find that both monomer and fibril diffusion on the surface are required to obtain length histograms as a function of time that resemble those observed in experiments. The best-fit simulated data can accurately describe the key features of experimental length histograms and suggests that the mobility of loosely bound amyloid species is crucial in regulating the kinetics of SMF. We determine that the mobility exponent for the size dependence of the DLA rate constants is α = 0.55 ± 0.05, which suggests that the diffusion of loosely bound surface fibrils roughly depends on the inverse of the square root of their size. These studies elucidate the influence of deposition rate and surface diffusion on the formation of amyloid fibrils through SMF. The method used here can be broadly adopted to study the diffusion and aggregation of peptides or proteins on various surfaces to investigate the role of chemical interactions in two-dimensional fibril formation and diffusion.

Fabrication of diverse nano-architectures through the self-assembly of a naphthalene diimide derivative bearing four carbamates

We found that naphthalene diimide (W2) bearing four carbamates bonds can organise various well-defined self-assembled nanostructures driven by π–π interaction and carbamate H-bonding.

Graphene oxide nanosheets in complex with cell penetrating peptides for oligonucleotides delivery

A new strategy for gene transfection using the nanocarrier of cell penetrating peptides (CPPs; PepFect14 (PF14) or PepFect14 (PF14) (PF221)) in complex with graphene oxide (GO) is reported. GO complexed with CPPs and plasmid (pGL3), splice correction oligonucleotides (SCO) or small interfering RNA (siRNA) are performed. Data show adsorption of CPPs and oligonucleotides on the top of the graphenic lamellar without any observed change of the particle size of GO. GO mitigates the cytotoxicity of CPPs and improves the material biocompatibility. Complexes of GO-pGL3-CPPs (CPPs; PF14 or PF221) offer 2.1-2.5 fold increase of the cell transfection compared to pGL3-CPPs (CPPs; PF14 or PF221). GO-SCO-PF14 assemblies effectively transfect the cells with an increase of >10-25 fold compared to the transfection using PF14. The concentration of GO plays a significant role in the material nanotoxicity and the transfection efficiency. The results open a new horizon in the gene treatment using CPPs and offer a simple strategy for further investigations.

Designed graphene-peptide nanocomposites for biosensor applications: A review

The modification of graphene with biomacromolecules like DNA, protein, peptide, and others extends the potential applications of graphene materials in various fields. The bound biomacromolecules could improve the biocompatibility and bio-recognition ability of graphene-based nanocomposites, therefore could greatly enhance their biosensing performances on both selectivity and sensitivity. In this review, we presented a comprehensive introduction and discussion on recent advance in the synthesis and biosensor applications of graphene-peptide nanocomposites. The biofunctionalization of graphene with specifically designed peptides, and the synthesis strategies of graphene-peptide (monomer, nanofibrils, and nanotubes) nanocomposites were demonstrated. On the other hand, the fabrication of graphene-peptide nanocomposite based biosensor architectures for electrochemical, fluorescent, electronic, and spectroscopic biosensing were further presented. This review includes nearly all the studies on the fabrication and applications of graphene-peptide based biosensors recently, which will promote the future developments of graphene-based biosensors in biomedical detection and environmental analysis.

Fluorine Functionalized Graphene Quantum Dots as Inhibitor against hIAPP Amyloid Aggregation

Fibrillar deposits of the human islet amyloid polypeptide (hIAPP) are considered as a root of Type II diabetes mellitus. Fluorinated graphene quantum dots (FGQDs) are new carbon nanomaterials with unique physicochemical properties containing highly electronegative F atoms. Herein we report a single step synthesis method of FGQDs with an inhibitory effect on aggregation and cytotoxicity of hIAPP in vitro. Highly fluorescent and water dispersible FGQDs, less than 3 nm in size, were synthesized by the microwave-assisted hydrothermal method. Efficient inhibition capability of FGQDs to amyloid aggregation was demonstrated. The morphologies of hIAPP aggregates were observed to change from the entangled long fibrils to short thin fibrils and amorphous aggregates in the presence of FGQDs. In thioflavin T fluorescence analysis, inhibited aggregation with prolonged lag time and reduced fluorescence intensity at equilibrium were observed when hIAPP was incubated together with FGQDs. Circular dichroism spectrum results reveal that FGQDs could inhibit conformational transition of the peptide from native structure to β-sheets. FGQDs could also rescue the cytotoxicity of INS-1 cells induced by hIAPP in a dose dependent manner. This study could be beneficial for design and preparation of inhibitors for amyloids, which is important for prevention and treatment of amyloidosis.

Dimensionality of carbon nanomaterial impacting on the modulation of amyloid peptide assembly

A wide variety of inorganic nanomaterials have been exploited so far for their great potential for biological applications. Some of these materials could be valid candidates to modulate the assembly of amyloid peptides, which is relevant to amyloid-related diseases. In this work, we reveal that a carbon nanomaterial can indeed modulate the assembly of amyloid peptides and, additionally, we show that this modulating effect is closely related to the dimensionality of the nanomaterials.