Encapsulation of particle ensembles in graphene nanosacks as a new route to multifunctional materials

Nanocarriers address intracellular barriers for efficient drug delivery, overcoming drug resistance, subcellular targeting and controlled release

The cellular barriers are major bottlenecks for bioactive compounds entering into cells to accomplish their biological functions, which limits their biomedical applications. Nanocarriers have demonstrated high potential and benefits for encapsulating bioactive compounds and efficiently delivering them into target cells by overcoming a cascade of intracellular barriers to achieve desirable therapeutic and diagnostic effects. In this review, we introduce the cellular barriers ahead of drug delivery and nanocarriers, as well as summarize recent advances and strategies of nanocarriers for increasing internalization with cells, promoting intracellular trafficking, overcoming drug resistance, targeting subcellular locations and controlled drug release. Lastly, the future perspectives of nanocarriers for intracellular drug delivery are discussed, which mainly focus on potential challenges and future directions. Our review presents an overview of intracellular drug delivery by nanocarriers, which may encourage the future development of nanocarriers for efficient and precision drug delivery into a wide range of cells and subcellular targets.

Graphene as a nano-delivery vehicle in agriculture - current knowledge and future prospects

Graphene has triggered enormous interest in, and exploration of, its applications in diverse areas of science and technology due to its unique properties. While graphene has displayed great potential as a nano-delivery system for drugs and biomolecules in biomedicine, its application as a nanocarrier in agriculture has only begun to be explored. Conventional fertilizers and agricultural delivery systems have a number of disadvantages, such as: fast release of the active ingredient, low delivery efficiency, rapid degradation and low stability that often leads to their over-application and consequent environmental problems. Advanced nano fertilizers with high carrier efficiency and slow and controlled release are now considered the gold standard for promoting agricultural sustainability while protecting the environment. Graphene's attractive properties include large surface area, chemical stability, mechanical stability, tunable surface chemistry and low toxicity making it a promising material on which to base agricultural delivery systems. Recent research has demonstrated considerable success in the use of graphene for agricultural applications, including its utilization as a delivery vehicle for plant nutrients and crop protection agents, as well as in post-harvest management of crops. This review, therefore, presents a comprehensive overview of the current status of graphene-based nanocarriers in agriculture. Additionally, the review outlines the surface functionalization methods used for effective molecular delivery, various strategies for nano-vehicle design and the underlying features necessary for a graphene-based agro-delivery system. Finally, the review discusses directions for further research in optimization of graphene-based nanocarriers.

Use of stimulatory responsive soft nanoparticles for intracellular drug delivery

Drug delivery has made tremendous advances in the last decade. Targeted therapies are increasingly common, with intracellular delivery highly impactful and sought after. Intracellular drug delivery systems have limitations due to imprecise and non-targeted release profiles. One way this can be addressed is through using stimuli-responsive soft nanoparticles, which contain materials with an organic backbone such as lipids and polymers. The choice of biomaterial is essential for soft nanoparticles to be responsive to internal or external stimuli. The nanoparticle must retain its integrity and payload in non-targeted physiological conditions while responding to particular intracellular environments where payload release is desired. Multiple internal and external factors could stimulate the intracellular release of drugs from nanoparticles. Internal stimuli include pH, oxidation, and enzymes, while external stimuli include ultrasound, light, electricity, and magnetic fields. Stimulatory responsive soft nanoparticulate systems specifically utilized to modulate intracellular delivery of drugs are explored in this review.

Antibacterial and Freshness-Preserving Mechanisms of Chitosan-Nano-TiO2-Nano-Ag Composite Materials

With chitosan, nano-TiO2 and nano-Ag as raw materials, nano-TiO2 and nano-TiO2-Ag were modified by a surface modifier-sodium laurate. Chitosan (CTS), chitosan-nano-TiO2 (CTS-TiO2), and chitosan-nano-TiO2-nano-Ag (CTS-TiO2-Ag) composite materials and corresponding films were prepared by a solution co-blending method. Then, the antibacterial performances of the above three types of materials against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis were compared. Moreover, potato and strawberry weight loss rates, peroxidase activity, and vitamin C contents after different film coating treatments were measured. Compared with CTS films, the CTS-TiO2-Ag and CTS-TiO2 composite films both showed better physical properties, and both demonstrated higher antibacterial effects, especially for E. coli. Measurement of physiological indices in fruits and vegetables showed that the freshness-preserving effect of CTS-TiO2-Ag coating films was the most significant. In all, the CTS-TiO2-Ag coating films can actively contribute to the storage of fruits and vegetables at room temperature, and better ensure product quality. Thus, such films are meaningful for research and development of new fruit freshness-keeping techniques and materials.

Solution Evaporation-Driven Crumpling and Assembling of Large-Accessible-Space, High-Mechanical-Strength Graphene/Carbon Nanotube Composite Nanoparticles

Crumpled graphene particles that are converted and assembled from 2D planar graphene sheets create a subtle material platform for widespread applications of graphene in a low-cost and scalable manner. However, such crumpled particles are suffering from small spatial availabilities in geometry and low strength in mechanical deformation due to the limited numbers and stabilities of connections among individual deformed graphene. Herein, we report, in both theoretical analysis and large-scale atomistic simulations, that a crumpled graphene composite nanoparticle with large accessible space and high mechanical strength can be achieved by encapsulating folded carbon nanotubes (CNTs) inside via a solvent evaporation-induced assembly approach. A unified energy-based theoretical model is developed to address the kinetic migration of both CNTs and graphene suspended in a liquid droplet and their crumpling and assembling mechanism into a composite particle by solution evaporation. The contact probability, surface ridge densities, and geometric size in assembled graphene/CNT composite nanoparticles are quantitatively extracted after the complete evaporation of liquid and are further correlated with their accessible space including accessible surface area and volume and mechanical strength. The coarse-grained molecular dynamics simulations are conducted to uncover structural and morphological evolution of graphene/CNT composite nanoparticles with solution evaporation, and the results show remarkable agreement with theoretical predictions. This study offers a theoretical foundation for synthesizing highly connected, mechanically enhanced, crumpled particles with tunable spatial porous structures by tailoring graphene and CNTs for applications in functional structures and devices.

Graphene and other 2D materials: a multidisciplinary analysis to uncover the hidden potential as cancer theranostics

Cancer represents one of the main causes of death in the world; hence the development of more specific approaches for its diagnosis and treatment is urgently needed in clinical practice. Here we aim at providing a comprehensive review on the use of 2-dimensional materials (2DMs) in cancer theranostics. In particular, we focus on graphene-related materials (GRMs), graphene hybrids, and graphdiyne (GDY), as well as other emerging 2DMs, such as MXene, tungsten disulfide (WS2), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), black phosphorus (BP), silicene, antimonene (AM), germanene, biotite (black mica), metal organic frameworks (MOFs), and others. The results reported in the scientific literature in the last ten years (>200 papers) are dissected here with respect to the wide variety of combinations of imaging methodologies and therapeutic approaches, including drug/gene delivery, photothermal/photodynamic therapy, sonodynamic therapy, and immunotherapy. We provide a unique multidisciplinary approach in discussing the literature, which also includes a detailed section on the characterization methods used to analyze the material properties, highlighting the merits and limitations of the different approaches. The aim of this review is to show the strong potential of 2DMs for use as cancer theranostics, as well as to highlight issues that prevent the clinical translation of these materials. Overall, we hope to shed light on the hidden potential of the vast panorama of new and emerging 2DMs as clinical cancer theranostics.

Stimuli-responsive nanocarriers for drug delivery, tumor imaging, therapy and theranostics

In recent years, much progress has been motivated in stimuli-responsive nanocarriers, which could response to the intrinsic physicochemical and pathological factors in diseased regions to increase the specificity of drug delivery. Currently, numerous nanocarriers have been engineered with physicochemical changes in responding to external stimuli, such as ultrasound, thermal, light and magnetic field, as well as internal stimuli, including pH, redox potential, hypoxia and enzyme, etc. Nanocarriers could respond to stimuli in tumor microenvironments or inside cancer cells for on-demanded drug delivery and accumulation, controlled drug release, activation of bioactive compounds, probes and targeting ligands, as well as size, charge and conformation conversion, etc., leading to sensing and signaling, overcoming multidrug resistance, accurate diagnosis and precision therapy. This review has summarized the general strategies of developing stimuli-responsive nanocarriers and recent advances, presented their applications in drug delivery, tumor imaging, therapy and theranostics, illustrated the progress of clinical translation and made prospects.

Multifunctional Magnetic Resonance Imaging Probes

Magnetic resonance imaging is characterized by high spatial resolution and unsurpassed soft tissue discrimination. Development and characterization of both intrinsic and extrinsic magnetic resonance (MR) imaging probes in the last decade has further strengthened the pivotal role MR imaging holds in the assessment of cancer in preclinical and translational settings. Sophisticated chemical modifications of a variety of nanoparticulate probes hold the potential to deliver valuable multifunctional tools applicable in diagnostics and/or treatment in human oncology. MR imaging suffers from a lack of sensitivity achievable by, e.g., nuclear medicine imaging methods. Advantages of including additional functionality/functionalities in a probe suitable for MR imaging are thus numerous, comprising the addition of fundamentally different imaging information (diagnostics), drug delivery (therapy), or the combination of both (theranostics). In recent years, we have witnessed a plethora of preclinical multimodal or multifunctional imaging probes being published mainly as proof-of-principle studies, yet only a handful are readily applicable in clinical settings. This chapter summarizes recent innovations in the development of multifunctional MR imaging probes and discusses the suitability of these probes for clinical transfer.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

Utilizing modules of different functions to construct a Janus-type membrane and derivative 3D Janus-type tube displaying synchronous trifunction of conductive aeolotropism, magnetism and luminescence

The microstructures and macrostructures play a crucial role in the properties and applications of multifunctional materials. Herein, microscopic partition and macroscopic partition are combined by devising and preparing different modules that can be elaborately devised to possess specific performances. A two-dimensional (2D) 3-module Janus-type membrane multifunctionalized by conductive aeolotropism, magnetism and luminescence (defined as 3M-CML Janus-type membrane) is constructed via electro-spinning. The modular structure of 3M-CML Janus-type membrane is obtained by devising and constructing three different modules, including luminescence module (denoted as L module), conductive aeolotropism-luminescence module (marked as C-L module) and magnetism-luminescence module (named as M-L module). The results prove that almost no mutual detrimental influences exist among different modules owing to the macroscopic modular structure and Janus-type structure, which effectively avoids the negative interactions among different materials. Tb(BA)₃phen/PVP nanofiber, [PMMA/Eu(BA)₃phen]//[PMMA/PANI] Janus-type nanoribbon and [PMMA/Tb(BA)₃phen]//[PMMA/Fe₃O₄] Janus-type nanoribbon are, respectively, selected as building units of the three modules, which further prevents the negative interactions among different materials and improves the versatility of 3M-CML Janus-type membrane. The luminescence, adjustable conductive aeolotropism and variable magnetism of 3M-CML Janus-type membrane are systematically discussed. Meanwhile, novel flexible four types of brand-new three-dimensional (3D) Janus-type tubes are obtained by rolling modularly devised 2D 3M-CML Janus-type membrane with different rolling schemes. As derivatives of the 2D 3M-CML Janus-type membranes, macroscopic 3D Janus-types tubes exhibit similar performances to 2D 3M-CML Janus-type membranes. The 2D Janus-type membrane and 3D Janus-type tube will have momentous applications in flexible electronics and nanodevices in the future.

Improved reductive transformation of iopromide by magnetite containing reduced graphene oxide nanosacks as electron shuttles

The novel application of magnetite containing reduced graphene oxide nanosacks (MrGO-N) as electron shuttles to improve the reductive degradation of pharmaceutical pollutant, iopromide (IOP), was evaluated. The MrGO-N were synthesized by ultrasonicated nebulization process, and their physicochemical characterization was performed by potentiometric titrations, zeta potential, high resolution transmission electron microscopy (HR-TEM), X-ray diffraction, as well as by Raman and Fourier transform infrared spectroscopies. Results demonstrated the thermal reduction of precursor graphene oxide sheets, the removal of different oxygenated groups, and the successful assembly of magnetite nanoparticles (MNP) in the graphene sacks. Also, reduction experiments revealed 72 % of IOP removal efficiency and up to 2.5-fold faster degradation of this pollutant performed with MrGO-N as redox catalysts in batch assays and with sulfide as electron donor. Chemical transformation pathway of IOP provides evidence of complete dehalogenation and further transformation of aromatic ring substituents. Greater redox-mediating ability of MrGO-N was observed, which was reflected in the catalytic activity of these nanomaterials during the reductive degradation of IOP. Transformation byproducts with simpler chemical structure were identified, which could lead to complete degradation by conventional methodologies in a complementary treatment process. Redox-mediating activity of MrGO-N could potentially be applied in wastewater treatment systems in order to facilitate the biodegradation of priority contaminants.

Novel application of magnetic nano-carbon composite as redox mediator in the reductive biodegradation of iopromide in anaerobic continuous systems

The redox-mediating capacity of magnetic reduced graphene oxide nanosacks (MNS) to promote the reductive biodegradation of the halogenated pollutant, iopromide (IOP), was tested. Experiments were performed using glucose as electron donor in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic conditions. Higher removal efficiency of IOP in the UASB reactor supplied with MNS as redox mediator was observed as compared with the control reactor lacking MNS. Results showed 82% of IOP removal efficiency under steady state conditions in the UASB reactor enriched with MNS, while the reactor control showed IOP removal efficiency of 51%. The precise microbial transformation pathway of IOP was elucidated by high-performance liquid chromatography coupled to mass spectroscopy (HPLC-MS) analysis. Biotransformation by-products with lower molecular weight than IOP molecule were identified in the reactor supplied with MNS, which were not detected in the reactor control, indicating the contribution of these magnetic nano-carbon composites in the redox conversion of this halogenated pollutant. Reductive reactions of IOP favored by MNS led to complete dehalogenation of the benzene ring and partial rupture of side chains of this pollutant, which is the first step towards its complete biodegradation. Possible reductive mechanisms that took place in the biodegradation of IOP were stated. Finally, the novel and successful application of magnetic graphene composites in a continuous bioreactor to enhance the microbial transformation of IOP was demonstrated.

Carbon Nano-Allotrope/Magnetic Nanoparticle Hybrid Nanomaterials as T2 Contrast Agents for Magnetic Resonance Imaging Applications

Magnetic resonance imaging (MRI) is the most powerful tool for deep penetration and high-quality 3D imaging of tissues with anatomical details. However, the sensitivity of the MRI technique is not as good as that of the radioactive or optical imaging methods. Carbon-based nanomaterials have attracted significant attention in biomaterial research in recent decades due to their unique physical properties, versatile functionalization chemistry, as well as excellent biological compatibility. Researchers have employed various carbon nano-allotropes to develop hybrid MRI contrast agents for improved sensitivity. This review summarizes the new research progresses in carbon-based hybrid MRI contrast agents, especially those reported in the past five years. The review will only focus on T2-weighted MRI agents and will be categorized by the different carbon allotrope types and magnetic components. Considering the strong trend in recent bio-nanotechnology research towards multifunctional diagnosis and therapy, carbon-based MRI contrast agents integrated with other imaging modalities or therapeutic functions are also covered.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Preparation of functionalized Pd/Fe-Fe3O4@MWCNTs nanomaterials for aqueous 2,4-dichlorophenol removal: Interactions, influence factors, and kinetics

Magnetic multi-walled carbon nanotubes (MWCNTs) were prepared to support Pd/Fe nanoparticles, inhibit the aggregation and passivation, and achieve magnetic separation to avoid the environmental risk of nanoparticles. Rapid adsorption of initial contaminant, steady dechlorination, and gradual desorption of final product was observed. The micromorphology, chemical structure, and components of the nanohybrids were comprehensively characterized by a series of analysis technologies, such as EDX, XRD, SEM, TEM, and XPS. The interactions between the nanohybrids compositions were discussed according to the characterization and experimental data. The whole insight of 2,4-dichlorophenol (2,4-DCP) adsorption- dechlorination-desorption was studied in detail, including the pathways, influence factors, dechlorination kinetics and selectivity. Weak acidity (pH=5.0 and 6.5) favored the 2,4-DCP removal. Satisfactory reactivity of the Pd/Fe-Fe3O4@MWCNTs nanohybrids was observed in five consecutive runs, and 99.2%, 89.6%, 92.1%, 99.8%, and 99.9% of 2,4-DCP was removed, respectively. Most of the final product (phenol) was steadily desorbed to the liquid phase, resulted in the re-exposure of active sites on the nanohybrids and maintained a longer activity.

Novel Electrospun Dual-Layered Composite Nanofibrous Membrane Endowed with Electricity-Magnetism Bifunctionality at One Layer and Photoluminescence at the Other Layer

Dual-layered composite nanofibrous membrane equipped with electrical conduction, magnetism and photoluminescence trifunctionality is constructed via electrospinning. The composite membrane consists of a polyaniline (PANI)/Fe₃O₄ nanoparticles (NPs)/polyacrylonitrile (PAN) tuned electrical-magnetic bifunctional nanofibrous layer at one side and a Eu(TTA)₃(TPPO)₂/polyvinylpyrrolidone (PVP) photoluminescent nanofibrous layer at the other side, and the two layers are tightly combined face-to-face together into the novel dual-layered composite membrane with trifunctionality. The electric conductivity and magnetism of electrical-magnetic bifunctionality can be respectively tunable via modulating the respective PANI and Fe₃O₄ NPs contents, and the highest electric conductivity approaches the order of 1 × 10^-2 S cm^-1. Predominant red emission at 615 nm can be obviously observed in the photoluminescent layer under 366 nm excitation. Moreover, the luminescent intensity of photoluminescent layer is almost unaffected by the electrical-magnetic bifunctional layer because of the fact that the photoluminescent materials have been successfully isolated from dark-colored PANI and Fe₃O₄ NPs. The novel dual-layered composite nanofibrous membrane with trifunctionality has potentials in many fields. Furthermore, the design philosophy and fabrication method for the dual-layered multifunctional membrane provide a new and facile strategy toward other membranes with multifunctionality.

Aerosol synthesis of phase-controlled iron-graphene nanohybrids through FeOOH nanorod intermediates

Iron-based nanoparticles form the basis for a host of sustainable alternative technologies based on this earth-abundant, low-toxicity element that can adopt a variety of oxidation states, crystal phases, and functions. Control of size, shape, and phase stability is a challenge for many nano-iron-based technologies, especially those involving Fe0 that is susceptible to oxidation under ambient conditions. This article presents a continuous method for hybridizing Fe-based nanoparticles with carbon in the form of graphene-encapsulated Fe-based particles with core-shell symmetry that allows flexible control of iron particle size, shape, and phase stability. The method uses FeOOH nanorods and graphene oxide as precursors, and subjects them to an aerosol-phase microdroplet drying and annealing process to yield a range of Fe/C nanohybrids whose structure can be controlled through adjustment of aerosol process temperature and post-synthesis thermal treatment conditions. We demonstrate that FeOOH nanorods can be successfully encapsulated in graphene, and transform during annealing into encapsulated Fe3O4 or Fe0 nanoparticles by reductive fragmentation, where the graphene nanosack acts as a carbothermic reductant. The hybrids are characterized by vibrating sample magnetometry and Cr(VI) reduction rates in aqueous media. The Fe0-graphene hybrids show high activity, good stability, and good recyclability in aqueous Cr(VI) removal due to the effect of graphene encapsulation. The present work suggests this rapid and continuous synthesis method can produce stable Fe-based materials, and can be extended to other metal systems, where graphene encapsulation can induce in situ reduction of metal oxide precursors into zero-valent metal-graphene hybrids.

Challenges in Liquid-Phase Exfoliation, Processing, and Assembly of Pristine Graphene

Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non-oxidized graphene) are described. General metrics are outlined that can be used to assess the quality and processability of various "graphene" products, as well as metrics that determine the potential for industrial scale-up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large-scale production.

A Highly Efficient Metal-Free Oxygen Reduction Electrocatalyst Assembled from Carbon Nanotubes and Graphene

A novel carbon-nanotube-graphene hybrid nanostructure is developed using an aerosol-assisted assembly approach. After doping with nitrogen and phosphorus, the prepared hybrid nanomaterials exhibit excellent electrocatalytic performance for oxygen reduction in both alkaline and acidic media. This research presents a continuous and low-cost route to prepare high-performance metal-free electrocatalysts while replacing Pt-based materials.

Optimization of upconversion luminescence of Nd3+-sensitized BaGdF5-based nanostructures and their application in dual-modality imaging and drug delivery

Nd³⁺-sensitized BaGdF₅:20%Yb³⁺/2%Er³⁺@BaGdF₅:10%Yb³⁺@BaNdF₅@BaGdF₅ nanoparticles for dual-model imaging and pH-triggered drug release.

rGO-Wrapped flowerlike Bi2Se3 nanocomposite: synthesis, experimental and simulation-based investigation on cold cathode applications

Bi₂Se₃ nanoflowers (NFs) – reduced graphene oxide (rGO) nanocomposite (BG) synthesized via cost-effective, ecofriendly and easy hydrothermal route: smart cold cathode for future display device.

Fast One-Pot Synthesis of MoS2/Crumpled Graphene p-n Nanonjunctions for Enhanced Photoelectrochemical Hydrogen Production

Aerosol processing enables the preparation of hierarchical graphene nanocomposites with special crumpled morphology in high yield and in a short time. Using modular insertion of suitable precursors in the starting solution, it is possible to synthesize different types of graphene-based materials ranging from heteroatom-doped graphene nanoballs to hierarchical nanohybrids made up by nitrogen-doped crumpled graphene nanosacks that wrap finely dispersed MoS2 nanoparticles. These materials are carefully investigated by microscopic (SEM, standard and HR TEM), diffraction (grazing incidence X-ray diffraction (GIXRD)) and spectroscopic (high resolution photoemission, Raman and UV-visible spectroscopy) techniques, evidencing that nitrogen dopants provide anchoring sites for MoS2 nanoparticles, whereas crumpling of graphene sheets drastically limits aggregation. The activity of these materials is tested toward the photoelectrochemical production of hydrogen, obtaining that N-doped graphene/MoS2 nanohybrids are seven times more efficient with respect to single MoS2 because of the formation of local p-n MoS2/N-doped graphene nanojunctions, which allow an efficient charge carrier separation.

Combined Photothermal and Surface-Enhanced Raman Spectroscopy Effect from Spiky Noble Metal Nanoparticles Wrapped within Graphene-Polymer Layers: Using Layer-by-layer Modified Reduced Graphene Oxide as Reactive Precursors

To fabricate functionally integrated hybrid nanoparticles holds high importance in biomedical applications and is still a challenging task. In this study, we report the first reduced graphene oxide (rGO)-nobel metal hybrid particles that present simultaneously the photothermal and surface-enhanced Raman spectroscopy (SERS) effect from the inorganic part and drug loading, dispersibility, and controllability features from LbL polyelectrolyte multilayers. The hybrid particles where spiky noble metal particles were wrapped within rGO-polyelectrolyte layers were prepared by a facile and controllable method. rGO template modified using polyethylenimine (PEI) and poly(acrylic acid) (PAA) via layer-by-layer technology served as the reactive precursors, and the morphologies of the particles could be facilely controlled via controlling the number of bilayers around the rGO template. The hybrid particle presented low cytotoxicity. After loading doxorubicin hydrochloride, the particles effectively induced cell death, and photothermal treatment further decreased cell viability. rGO-Ag hybrid particles could be prepared similarly. We expect the reported method provides an effective strategy to prepare rGO-noble metal hybrid nanoparticles that find potential biomedical applications.

Crumpled graphene nanoreactors

Nanoreactors are material structures that provide engineered internal cavities that create unique confined nanoscale environments for chemical reactions. Crumpled graphene nanoparticles or "nanosacks" may serve as nanoreactors when filled with reactive or catalytic particles and engineered for a specific chemical function. This article explores the behavior of crumpled graphene nanoreactors containing nanoscale ZnO, Ag, Ni, Cu, Fe, or TiO2 particles, either alone or in combination, in a series of case studies designed to reveal their fundamental behaviors. The first case study shows that ZnO nanoparticles undergo rapid dissolution inside the nanoreactor cavity accompanied by diffusive release of soluble products to surrounding aqueous media through the irregular folded shell. This behavior demonstrates the open nature of the sack structure, which facilitates rapid small-molecule exchange between inside and outside that is a requirement for nanoreactor function. In a case study on copper and silver nanoparticles, encapsulation in graphene nanoreactors is shown in some cases to enhance their oxidation rate in aqueous media, which is attributed to electron transfer from the metal core to graphene that bypasses surface oxides and allows reduction of molecular oxygen on the high-area graphene shell. Nanoreactors also allow particle-particle electron transfer interactions that are mediated by the connecting conductive graphene, which give rise to novel behaviors such as galvanic protection of Ag nanoparticles in Ag/Ni-filled nanoreactors, and the photochemical control of Ag-ion release in Ag/TiO2-filled nanoreactors. It is also shown that internal graphene structures within the sacks provide pockets that reduce particle mobility and inhibit particle sintering during thermal treatment. Finally, these novel behaviors are used to suggest and demonstrate several potential applications for graphene nanoreactors in catalysts, controlled release, and environmental remediation.

Tailored Crumpling and Unfolding of Spray-Dried Pristine Graphene and Graphene Oxide Sheets

For the first time, pristine graphene can be controllably crumpled and unfolded. The mechanism for graphene is radically different than that observed for graphene oxide; a multifaced crumpled, dimpled particle morphology is seen for pristine graphene in contrast to the wrinkled, compressed surface of graphene oxide particles, showing that surface chemistry dictates nanosheet interactions during the crumpling process. The process demonstrated here utilizes a spray-drying technique to produce droplets of aqueous graphene dispersions and induce crumpling through rapid droplet evaporation. For the first time, the gradual dimensional transition of 2D graphene nanosheets to a 3D crumpled morphology in droplets is directly observed; this is imaged by a novel sample collection device inside the spray dryer itself. The degree of folding can be tailored by altering the capillary forces on the dispersed sheets during evaporation. It is also shown that the morphology of redispersed crumpled graphene powder can be controlled by solvent selection. This process is scalable, with the ability to rapidly process graphene dispersions into powders suitable for a variety of engineering applications.

Smart MoS2/Fe3O4 Nanotheranostic for Magnetically Targeted Photothermal Therapy Guided by Magnetic Resonance/Photoacoustic Imaging

The ability to selectively destroy cancer cells while sparing normal tissue is highly desirable during the cancer therapy. Here, magnetic targeted photothermal therapy was demonstrated by the integration of MoS₂ (MS) flakes and Fe₃O₄ (IO) nanoparticles (NPs), where MoS₂ converted near-infrared (NIR) light into heat and Fe₃O₄ NPs served as target moiety directed by external magnetic field to tumor site. The MoS₂/Fe₃O₄ composite (MSIOs) functionalized by biocompatible polyethylene glycol (PEG) were prepared by a simple two-step hydrothermal method. And the as-obtained MSIOs exhibit high stability in bio-fluids and low toxicity in vitro and in vivo. Specifically, the MSIOs can be applied as a dual-modal probe for T₂-weighted magnetic resonance (MR) and photoacoustic tomography (PAT) imaging due to their superparamagnetic property and strong NIR absorption. Furthermore, we demonstrate an effective result for magnetically targeted photothermal ablation of cancer. All these results show a great potential for localized photothermal ablation of cancer spatially/timely guided by the magnetic field and indicated the promise of the multifunctional MSIOs for applications in cancer theranostics.

Three-dimensional graphene-based composites for energy applications

Three-dimensional (3D) graphene-based composites have drawn increasing attention for energy applications due to their unique structures and properties. By combining the merits of 3D graphene (3DG), e.g., a porous and interconnected network, a high electrical conductivity, a large accessible surface area, and excellent mechanical strength and thermal stability, with the high chemical/electrochemical activities of active materials, 3DG-based composites show great promise as high-performance electrode materials in various energy devices. This article reviews recent progress in 3DG-based composites and their applications in energy storage/conversion devices, i.e., supercapacitors, lithium-ion batteries, dye-sensitized solar cells, and fuel cells.

Graphene-based nanomaterials as molecular imaging agents

Molecular imaging (MI) is a noninvasive, real-time visualization of biochemical events at the cellular and molecular level within tissues, living cells, and/or intact objects that can be advantageously applied in the areas of diagnostics, therapeutics, drug discovery, and development in understanding the nanoscale reactions including enzymatic conversions and protein-protein interactions. Consequently, over the years, great advancement has been made in the development of a variety of MI agents such as peptides, aptamers, antibodies, and various nanomaterials (NMs) including single-walled carbon nanotubes. Recently, graphene, a material popularized by Geim & Novoselov, has ignited considerable research efforts to rationally design and execute a wide range of graphene-based NMs making them an attractive platform for developing highly sensitive MI agents. Owing to their exceptional physicochemical and biological properties combined with desirable surface engineering, graphene-based NMs offer stable and tunable visible emission, small hydrodynamic size, low toxicity, and high biocompatibility and thus have been explored for in vitro and in vivo imaging applications as a promising alternative of traditional imaging agents. This review begins by describing the intrinsic properties of graphene and the key MI modalities. After which, we provide an overview on the recent advances in the design and development as well as physicochemical properties of the different classes of graphene-based NMs (graphene-dye conjugates, graphene-antibody conjugates, graphene-nanoparticle composites, and graphene quantum dots) being used as MI agents for potential applications including theranostics. Finally, the major challenges and future directions in the field will be discussed.

Two-dimensional graphene analogues for biomedical applications

In this critical review, we summarize the state-of-the-art progress of two-dimensional graphene analogues with a particular focus on biomedical applications.

Antioxidant chemistry of graphene-based materials and its role in oxidation protection technology

Two-dimensional nanomaterials have potential as a new class of antioxidants that combine physical barrier function with ultrahigh surface area for free radical scavenging. This work presents the first measurements of the chemical reactivities of graphene-based materials toward a set of model free radicals and reactive oxygen species using electron paramagnetic resonance spectroscopy (EPR) and sacrificial dye protection assays. Graphene-based materials are shown to protect a variety of molecular targets from oxidation by these species, and to be highly effective as hydroxyl-radical scavengers. When the hydroxyl radical is produced photolytically, the overall antioxidant effect is a combination of preventative antioxidant activity (UV absorption) and ˙OH radical scavenging. Few-layer graphene is more active than monolayer graphene oxide, despite its lower surface area, which indicates that the primary scavenging sites are associated with the sp(2)-carbon network rather than oxygen-containing functional groups. To explain this trend, we propose that GO is a weak hydrogen donor, due to the non-phenolic nature of most OH groups on GO, which reside at basal sp(3)-carbon sites that do not allow for radical resonance stabilization following hydrogen donation. As an example application of graphene antioxidant behavior, we show that encapsulation of TiO2 nanoparticles in graphene nanosacks reduces undesired photo-oxidative damage to nearby organic target molecules, which suggests graphene encapsulation as a new approach to managing adverse environmental or health impacts of redox-active nanomaterials.

Multifunctional hybrid nanopatches of graphene oxide and gold nanostars for ultraefficient photothermal cancer therapy

Multifunctional hybrid nanomaterials with enhanced therapeutic efficiency at physiologically safe dosages for externally triggered, image-guided therapy are highly attractive for nanomedicine. Here, we demonstrate a novel class of multifunctional hybrid nanopatches comprised of graphene oxide (GO) and gold nanostars for enhanced photothermal effect and image-guided therapy. The hybrid nanopatches with tunable localized surface plasmon resonance into the near-infrared therapeutic window (650-900 nm) were realized using a biofriendly method that obviates the need for toxic shape-directing agents. Internalization of the intact nanopatches into epithelial breast cancer cells was confirmed by Raman imaging, transmission electron microscopy, and inductively coupled plasma mass spectrometry. It appears that the amphipathic nature and the large surface area of the graphene oxide enable it to serve as a soft, flexible, and biocompatible intracellular carrier for the in situ grown plasmonic nanostructures and provide long-term biocompatibility with extremely low cytotoxicity. Apart from a remarkably improved photothermal effect compared to that of either of the components at very low dosages of the hybrids (10 μg/mL GO) and using a low laser power (0.75 W cm(-2)), the hybrid nanopatches exhibit strong Raman scattering, making them excellent candidates for bioimaging, diagnostics, and image-guided therapy applications.

Facile fabrication of single-phase multifunctional BaGdF5 nanospheres as drug carriers

Multifunctional BaGdF5 nanospheres with mesoporous, luminescent, and magnetic properties have been successfully synthesized with the assistance of trisodium citrate by a hydrothermal method. The mesoporous structure is revealed by scanning electron microscope and transmission electron microscope images as well as N2 adsorption-desorption isotherm. The as-synthesized BaGdF5 nanospheres exhibit an intense broad bluish emission (centered at 450 nm) under the excitation of 390 nm, which might originate from the CO2·(-) radical-related defect produced by Cit(3-) groups. It is also shown that these BaGdF5 nanospheres brightened the T1-weighted images, suggesting that they could act as T1 contrast agents for magnetic resonance imaging. Using metformin hydrochloride as the model drug, the luminescent porous spheres show good drug storage/release capability. Furthermore, the emission intensity varies as a function of the cumulative drug release, making the drug-carrying system easily trackable and monitorable by detecting the luminescence intensity. Additionally, the paramagnetic property, originating from the unpaired electrons of Gd(3+) ions, opens the possibility of directing the magnetic targeted carrier to the pathological site by magnetic field gradient.

Self-adaptive strain-relaxation optimization for high-energy lithium storage material through crumpling of graphene

High-energy lithium battery materials based on conversion/alloying reactions have tremendous potential applications in new generation energy storage devices. However, these applications are limited by inherent large volume variations and sluggish kinetics. Here we report a self-adaptive strain-relaxed electrode through crumpling of graphene to serve as high-stretchy protective shells on metal framework, to overcome these limitations. The graphene sheets are self-assembled and deeply crumpled into pinecone-like structure through a contraction-strain-driven crumpling method. The as-prepared electrode exhibits high specific capacity (2,165 mAh g(-1)), fast charge-discharge rate (20 A g(-1)) with no capacity fading in 1,000 cycles. This kind of crumpled graphene has self-adaptive behaviour of spontaneous unfolding-folding synchronized with cyclic expansion-contraction volumetric variation of core materials, which can release strain and maintain good electric contact simultaneously. It is expected that such findings will facilitate the applications of crumpled graphene and the self-adaptive materials.

Facile aerosol synthesis and characterization of ternary crumpled graphene-TiO₂-magnetite nanocomposites for advanced water treatment

In this work, the synthesis and characterization of multifunctional crumpled graphene-based ternary nanocomposite photocatalysts for advanced water treatment applications is described. Currently, a major hurdle for the scale-up and optimization of aqueous, graphene-based photocatalysts is restacking of graphene nanosheets due to strong π-π interactions. To overcome this hurdle, a fast and facile aerosol technique to synthesize monomeric, aggregation-resistant, crumpled graphene-based photocatalysts was developed. The aerosol route utilizes water evaporation-induced confinement forces to effectively crumple graphene oxide and subsequently encapsulate commercially available TiO2 and magnetite nanoparticles. The as-synthesized crumpled graphene-TiO2-magnetite (GOTIM) ternary core-shell nanostructures are shown to possess superior aqueous-based photocatalytic properties (over a 20-fold enhancement in some cases) compared to TiO2 alone. Total GOTIM photocatalytic reactivity is confirmed to also include efficient photoreduction reaction pathways, in addition to expected oxidation routes typical of TiO2-based photocatalysts, significantly expanding photocatalytic application potential compared to TiO2 alone. Reaction kinetics and proposed mechanisms (both oxidative and reductive) are described for a model organic compound, here as methyl orange. Further, with the addition of hole scavengers such as EDTA, and/or lowering the O2 concentration, we demonstrate enhancement of photocatalyzed reduction reactions, suggesting potential for directed, controlled reduction applications. In addition to robust aqueous stability, low-field magnetic susceptibility is demonstrated, allowing for low-energy, in situ material separations, which are critical for material recycling and reuse.

Integrated graphene/nanoparticle hybrids for biological and electronic applications

The development of novel graphene/nanoparticle hybrid materials is currently the subject of tremendous research interest. The intrinsic exceptional assets of both graphene (including graphene oxide and reduced graphene oxide) and nanoparticles render their hybrid materials synergic properties that can be useful in various applications. In this feature review, we highlight recent developments in graphene/nanoparticle hybrids and their promising potential in electronic and biological applications. First, the latest advances in synthetic methods for the preparation of the graphene/nanoparticle hybrids are introduced, with the emphasis on approaches to (1) decorate nanoparticles onto two-dimensional graphene and (2) wrap nanoparticles with graphene sheets. The pros and cons of large-scale synthesis are also discussed. Then, the state-of-the-art of graphene/nanoparticle hybrids in electronic and biological applications is reviewed. For electronic applications, we focus on the advantages of using these hybrids in transparent conducting films, as well as energy harvesting and storage. Biological applications, electrochemical biosensing, bioimaging, and drug delivery using the hybrids are showcased. Finally, the future research prospects and challenges in this rapidly developing area are discussed.

Hydrogenation-assisted graphene origami and its application in programmable molecular mass uptake, storage, and release

The malleable nature of atomically thin graphene makes it a potential candidate material for nanoscale origami, a promising bottom-up nanomanufacturing approach to fabricating nanobuilding blocks of desirable shapes. The success of graphene origami hinges upon precise and facile control of graphene morphology, which still remains as a significant challenge. Inspired by recent progresses on functionalization and patterning of graphene, we demonstrate hydrogenation-assisted graphene origami (HAGO), a feasible and robust approach to enabling the formation of unconventional carbon nanostructures, through systematic molecular dynamics simulations. A unique and desirable feature of HAGO-enabled nanostructures is the programmable tunability of their morphology via an external electric field. In particular, we demonstrate reversible opening and closing of a HAGO-enabled graphene nanocage, a mechanism that is crucial to achieve molecular mass uptake, storage, and release. HAGO holds promise to enable an array of carbon nanostructures of desirable functionalities by design. As an example, we demonstrate HAGO-enabled high-density hydrogen storage with a weighted percentage exceeding the ultimate goal of US Department of Energy.

Crumpled graphene-molybdenum oxide composite powders: preparation and application in lithium-ion batteries

Crumpled graphene-MoO2 composite powders are directly prepared by means of spray pyrolysis and from a stable graphene oxide colloidal solution in the presence of Mo ions. The crumpled graphene-MoO2 composite powders are transformed into MoO3 -based composite powders after post-treatment at 300 °C. The transmission electron microscopy and dot-mapping images of the post-treatment composite powders show uniform distribution of MoO3 nanocrystals in the crumpled graphene powders. The two typical D and G bands of graphene are observed at 1350 and 1590 cm(-1) , respectively, in the Raman spectrum of the graphene-MoO3 composite. In addition, the crumpled graphene-MoO3 powders exhibit superior electrochemical behavior compared to that of pure MoO3 as an anode material for lithium-ion batteries. The initial discharge capacities of the graphene-MoO3 composite and bare MoO3 powders at a current density of 2 A g(-1) are 1490 and 1225 mA h g(-1) , respectively. The capacity retention of the graphene-MoO3 composite is 87 % after the first cycle, whereas that of bare MoO3 is 47 %, as measured after 100 cycles. The reversible discharge capacity of the graphene-MoO3 composite decreases slightly from 1228 to 845 mA h g(-1) as the current density increases from 0.5 to 3 A g(-1) .

Fabrication of quasi-cubic Fe3O4@rGO composite via a colloid electrostatic self-assembly process for supercapacitors

Superior behavior for supercapacitors highlight the potential applications of CFGC in energy storage issues.

Targeting chemophotothermal therapy of hepatoma by gold nanorods/graphene oxide core/shell nanocomposites

Nanographene oxide (NGO) are highly suitable to be the shells of inorganic nanomaterials to enhance their biocompatibility and hydrophilicity for biomedical applications while retaining their useful photonic, magnetic, or radiological functions. In this study, a novel nanostructure with gold nanorods (AuNRs) encapsulated in NGO shells is developed to be an ultraefficient chemophotothermal cancer therapy agent. The NGO shells decrease the toxicity of surfactant-coated AuNRs and provide anchor points for the conjugation of hyaluronic acid (HA). The HA-conjugated NGO-enwrapped AuNR nanocomposites (NGOHA-AuNRs) perform higher photothermal efficiency than AuNRs and have the capability of targeting hepatoma Huh-7 cells. NGOHA-AuNR is applied to load doxorubicin (DOX), and it exhibits pH-responsive and near-infrared light-triggered drug-release properties. Chemophotothermal combined therapy by NGOHA-AuNRs-DOX performs 1.5-fold and 4-fold higher targeting cell death rates than single chemotherapy and photothermal therapy, respectively, with biosafety to nontargeting cells simultaneously. Furthermore, our strategy could be extended to constructing other NGO-encapsulated functional nanomaterial-based carrier systems.