Multifunctional Graphene Oxide‐based Triple Stimuli‐Responsive Nanotheranostics

Construction of multifunctional stimuli‐responsive nanosystems intelligently responsive to inner physiological and/or external irradiations based on nanobiotechnology can enable the on‐demand drug release and improved diagnostic imaging to mitigate the side‐effects of anticancer drugs and enhance the diagnostic/therapeutic outcome simultaneously. Here, a triple‐functional stimuli‐responsive nanosystem based on the co‐integration of superparamagnetic Fe₃O₄ and paramagnetic MnO_x nanoparticles (NPs) onto exfoliated graphene oxide (GO) nanosheets by a novel and efficient double redox strategy (DRS) is reported. Aromatic anticancer drug molecules can interact with GO nanosheets through supramolecular π stacking to achieve high drug loading capacity and pH‐responsive drug releasing performance. The integrated MnO_x NPs can disintegrate in mild acidic and reduction environment to realize the highly efficient pH‐responsive and reduction‐triggered T₁‐weighted magnetic resonance imaging (MRI). Superparamagnetic Fe₃O₄ NPs can not only function as the T₂‐weighted contrast agents for MRI, but also response to the external magnetic field for magnetic hyperthermia against cancer. Importantly, the constructed biocompatible GO‐based nanoplatform can inhibit the metastasis of cancer cells by downregulating the expression of metastasis‐related proteins, and anticancer drug‐loaded carrier can significantly reverse the multidrug resistance (MDR) of cancer cells.     

Conductive Graphitic Channel in Graphene Oxide‐Based Memristive Devices

Electrically insulating graphene oxide with various oxygen‐functional groups is a novel material as an active layer in resistive switching memories via reduction process. Although many research groups have reported on graphene oxide‐based resistive switching memories, revealing the origin of conducting path in a graphene oxide active layer remains a critical challenge. Here nanoscale conductive graphitic channels within graphene oxide films are reported using a low‐voltage spherical‐aberration‐corrected transmission electron microscopy. Simultaneously, these channels with reduced graphene oxide nanosheets induced by the detachment of oxygen groups are verified by Raman intensity ratio map and conductive atomic force microscopy. It is also clearly revealed that Al metallic protrusions, which are generated in the bottom interface layer, assist the local formation of conductive graphitic channels directly onto graphene oxide films by generating a local strong electric field. This work provides essential information for future carbon‐based nanoelectronic devices.     

Structure‐Properties Relationship in Iron Oxide‐Reduced Graphene Oxide Nanostructures for Li‐Ion Batteries

Non‐aqueous sol‐gel routes involving the reaction of metal oxide precursors in organic solvents (e.g., benzyl alcohol) at moderate temperature and pressure, offer advantages such as high purity, high reproducibility and the ability to control the crystal growth without the need of using additional ligands. In this paper, a study carried out on a series of iron oxide/reduced graphene oxide composites is presented to elucidate a structure‐properties relationship leading to an improved electrochemical performance of such composites. Moreover, it is demonstrated that the easy production of the composites in a variety of temperature and composition ranges, allows a fine control over the final particles size, density and distribution. The materials obtained are remarkable in terms of the particle's size homogeneity and dispersion onto the reduced graphene oxide surface. Moreover, the synthesis method used to obtain the graphene oxide clearly affects the performances of the final composites through the control of the restacking of the reduced graphene oxide sheets. It is shown that a homogeneous and less defective reduced graphene oxide enables good electrochemical performances even at high current densities (over 500 mAh/g delivered at current densities as high as 1600 mA/g). The electrochemical properties of improved samples reach the best compromise between specific capacity, rate capability and cycle stability reported so far.     

Capacitive Enhancement Mechanisms and Design Principles of High‐Performance Graphene Oxide‐Based All‐Solid‐State Supercapacitors

Graphene oxide (GO)‐based all‐solid‐state supercapacitors (GO‐A3Ss) are superior over liquid electrolyte‐based supercapacitors and capable of being integrated on a single chip in various geometry shapes for the use of future smart wearable electronics field as a fast energy storage device, but their capacitance need to be improved. Here, a new approach has been developed for enhancing the capacitive capability of the supercapacitors through molecular dynamics simulations with the first‐principle input. A theoretical model of charge storage is developed to understand the unique capacitive enhancement mechanism and to predict the capacitance of the GO‐A3Ss, which agrees well with the experimental observations. A novel supercapacitor with GO and reduced graphene oxide (rGO) alternatively layered structures is designed based on the model, and its energy density is the highest among conventional supercapacitors using liquid electrolytes and all‐solid‐state supercapacitors using aerogels or hydrogels as the solid‐state electrolyte. Based on the predictions, two new types of high‐performance GO/rGO multilayered capacitors are proposed to meet different practical applications. The results of this work provide an approach for the design of high‐performance all‐solid‐state supercapacitors based on GO and rGO materials.     

Ultra‐Broadband Wide‐Angle Terahertz Absorption Properties of 3D Graphene Foam

As a next generation of detection technology, terahertz technology is very promising. In this work, a highly efficient terahertz wave absorber based on 3D graphene foam (3DG) is first reported. Excellent terahertz absorption property at frequency ranging from 0.1 to 1.2 THz is obtained owing to faint surface reflection and enormous internal absorption. By precise control of the constant properties for 3DG, the reflection loss (RL) value of 19 dB is acquired and the qualified frequency bandwidth (with RL value over 10 dB) covers 95% of the entire measured bandwidth at normal incidence, which far surpasses most reported materials. More importantly, the terahertz absorption performance of 3DG enhances obviously with increasing the incidence while majority of materials become invalid at oblique incidence, instead. At the incidence of 45°, the maximum RL value increases 50% from 19 to 28.6 dB and the qualified frequency bandwidth covers 100% of the measured bandwidth. After considering all core indicators involving density, qualified bandwidth, and RL values, the specific average terahertz absorption (SATA) property is investigated. The SATA value of 3DG is over 3000 times higher than those of other materials in open literatures.     

A High‐Performance Graphene Oxide‐Doped Ion Gel as Gel Polymer Electrolyte for All‐Solid‐State Supercapacitor Applications

A high‐performance graphene oxide (GO)‐doped ion gel (P(VDF‐HFP)‐EMIMBF₄‐GO gel) is prepared by exploiting copolymer (poly(vinylidene fluoride‐hexafluoro propylene), P(VDF‐HFP)) as the polymer matrix, ionic liquid (1‐ethyl‐3‐methylimidazolium tetrafluoroborate, EMIMBF₄) as the supporting electrolyte, and GO as the ionic conducting promoter. This GO‐doped ion gel demonstrates significantly improved ionic conductivity compared with that of pure ion gel without the addition of GO, due to the homogeneously distributed GO as a 3D network throughout the GO‐doped ion gel by acting like a ion “highway” to facilitate the ion transport. With the incorporation of only a small amount of GO (1 wt%) in ion gel, there has been a dramatic improvement in ionic conductivity of about 260% compared with that of pure ion gel. In addition, the all‐solid‐state supercapacitor is fabricated and measured at room temperature using the GO‐doped ion gel as gel polymer electrolyte, which demonstrates more superior electrochemical performance than the all‐solid‐state supercapacitor with pure ion gel and the conventional supercapacitor with neat EMIMBF₄, in the aspect of smaller internal resistance, higher capacitance performance, and better cycle stability. These excellent performances are due to the high ionic conductivity, excellent compatibility with carbon electrodes, and long‐term stability of the GO‐doped ion gel.     

Graphene Oxide‐Template Controlled Cuboid‐Shaped High‐Capacity VS4 Nanoparticles as Anode for Sodium‐Ion Batteries

Room‐temperature sodium‐ion batteries have attracted great attentions for large‐scale energy storage applications in renewable energy. However, exploring suitable anode materials with high reversible capacity and cyclic stability is still a challenge. The VS₄, with parallel quasi‐1D chains structure of V⁴⁺(S₂^2?)₂, which provides large interchain distance of 5.83 Å and high capacity, has showed great potential for sodium storage. Here, the uniform cuboid‐shaped VS₄ nanoparticles are prepared as anode for sodium‐ion batteries by the controllable of graphene oxide (GO)‐template contents. It exhibits superb electrochemical performances of high‐specific charge capacity (≈580 mAh·g^?1 at 0.1 A·g^?1), long‐cycle‐life (≈98% retain at 0.5 A·g?¹ after 300 cycles), and high rates (up to 20 A·g^?1). In addition, electrolytes are optimized to understand the sodium storage mechanism. It is thus demonstrated that the findings have great potentials for the applications in high‐performance sodium‐ion batteries.     

pH‐Responsive Cyanine‐Grafted Graphene Oxide for Fluorescence Resonance Energy Transfer‐Enhanced Photothermal Therapy

Stimuli‐responsive anticancer agents are of particular interest in the field of cancer therapy. Nevertheless, so far stimuli‐responsive photothermal agents have been explored with limited success for cancer photothermal therapy (PTT). In this work, as a proof‐of‐concept, a pH‐responsive photothermal nanoconjugate for enhanced PTT efficacy, in which graphene oxide (GO) with broad NIR absorbance and effective photothermal conversion efficiency is selected as a typical model receptor of fluorescence resonance energy transfer (FRET), and grafted cyanine dye (e.g., Cypate) acts as the donor of near‐infrared fluorescence (NIRF), is reported for the first time. The conjugate of Cypate‐grafted GO exhibits different conformations in aqueous solutions at various pH, which can trigger pH‐dependent FRET effect between GO and Cypate and thus induce pH‐responsive photothermal effect of GO‐Cypate. GO‐Cypate exhibits severe cell damage owing to the enhanced photothermal effect in lysosomes, and thus generate synergistic PTT efficacy with tumor ablation upon photoirradiation after a single‐dose intravenous injection. The photothermal nanoconjugate with broad NIR absorbance as the effective receptor of FRET can smartly convert emitted NIRF energy from donor cyanine dye into additional photothermal effect for improving PTT. These results suggest that the smart nanoconjugate can act as a promising stimuli‐responsive photothermal nanoplatform for cancer therapy.     

Graphene‐Oxide‐Conjugated Polymer Hybrid Materials for Calmodulin Sensing by Using FRET Strategy

The conformation of calmodulin (CaM) changes from closed configuration to open one, converting to a claviform dumbbell‐shaped biomolecule upon Ca²⁺‐binding. A hybrid probe of graphene oxide (GO) cationic conjugated polymer for detection of the conformation transition of CaM by using FRET technique is demonstrated. The stronger hydrophobic interaction and weaker electrostatic repulsion leads to more CaM adsorption to the surface of GO upon binding with Ca²⁺ than that of CaM in the absence of Ca²⁺ (apoCaM), resulting in much farther proximity between poly[(9,9‐bis(6′‐N,N,N‐trimethy­lammonium)hexyl)‐fluorenylene phenylene dibromide] (PFP) and green fluorescent protein labeled at the N‐terminus of CaM and therefore much weaker FRET efficiency for PFP/Ca²⁺/CaM in comparison with that of PFP/apoCaM in the presence of GO. Notably, the assembly of CaM with GO is quantitatively and reversibly controlled by Ca²⁺ ions.     

Fluorinated Graphene in Interface Engineering of Ge‐Based Nanoelectronics

Germanium is a promising candidate to replace silicon in nanoelectronics due to its significantly higher electron and hole mobilities. However, the unstable germanium oxide formed at the interface between the channel and dielectric layer has impeded the progress of Ge‐based nanoelectronics. By taking advantage of the impermeability of graphene, it is discovered that the insulating fluorinated graphene is able to act as an efficient diffusion barrier layer to suppress the formation of the unstable interfacial oxide in Ge‐based devices. The Ge‐based device with the fluorinated graphene exhibits negligible capacitance versus voltage hysteresis, extremely low leakage, and superior equivalent oxide thickness. First‐principles calculations reveal that interfacial diffusion, which would otherwise be unmanageable, is sufficiently obstructed by the fluorinated graphene. This new structure is expected to expedite the implementation of germanium as a channel material in next‐generation nanoelectronic devices.     

High‐Nanofiller‐Content Graphene Oxide–Polymer Nanocomposites via Vacuum‐Assisted Self‐Assembly

Highly ordered, homogeneous polymer nanocomposites of layered graphene oxide are prepared using a vacuum‐assisted self‐assembly (VASA) technique. In VASA, all components (nanofiller and polymer) are pre‐mixed prior to assembly under a flow, making it compatible with either hydrophilic poly(vinyl alcohol) (PVA) or hydrophobic poly(methyl methacrylate) (PMMA) for the preparation of composites with over 50 wt% filler. This process is complimentary to layer‐by‐layer assembly, where the assembling components are required to interact strongly (e.g., via Coulombic attraction). The nanosheets within the VASA‐assembled composites exhibit a high degree of order with tunable intersheet spacing, depending on the polymer content. Graphene oxide–PVA nanocomposites, prepared from water, exhibit greatly improved modulus values in comparison to films of either pure PVA or pure graphene oxide. Modulus values for graphene oxide–PMMA nanocomposites, prepared from dimethylformamide, are intermediate to those of the pure components. The differences in structure, modulus, and strength can be attributed to the gallery composition, specifically the hydrogen bonding ability of the intercalating species     

Lineage‐Specific Commitment of Stem Cells with Organic and Graphene Oxide–Functionalized Nanofibers

Controlling the differentiation to certain lineages is the main goal of current stem cell research, which might exploit new routes based on the interaction of cells with nanomaterials. Here it is shown that primary neurospheres from dental pulp stem cells grown on combinatorial surfaces with different fibrous morphology and graphene oxide functionalization exhibit different differentiation propensity. The developed materials strongly influence the stem cell fate, as highlighted by morphological, immunofluorescence, molecular biology, and functional analyses. Instructive cues lead to the increased expression of markers that are characteristic of selective differentiation into osteoblasts, glial cells, fibroblasts, and neurons even in basal medium conditions, and randomly oriented fibers are found to revert neuronal precommitment and to trigger osteoblastic differentiation. Graphene oxide coatings lead instead to the relatively enhanced expression of genes typical of either glial or neuronal commitment, depending on the underlying nanofibrous morphology. The mechanisms addressing cell fate are investigated, highlighting the correlation of wetting anisotropy and protein adsorption capacity of different surfaces, ultimate cell conformational changes reflected by skeletal and nuclear elongation, and directed cell commitment. Cues from the different surfaces are therefore lineage‐specific, unveiling remarkable potentialities for cellular programming by means of nanomaterials.     

Graphene Oxide‐Cyclic R10 Peptide Nuclear Translocation Nanoplatforms for the Surmounting of Multiple‐Drug Resistance

Multidrug resistance resulting from a variety of defensive pathways in cancer has become a global concern with a considerable impact on the mortality associated with the failure of traditional chemotherapy. Therefore, further research and new therapies are required to overcome this challenge. In this work, a cyclic R10 peptide (cR₁₀) is conjugated to polyglycerol‐covered nanographene oxide to engineer a nanoplatform for the surmounting of multidrug resistance. The nuclear translocation of the nanoplatform, facilitated by cR₁₀ peptide, and subsequently, a laser‐triggered release of the loaded doxorubicin result in efficient anticancer activity confirmed by both in vitro and in vivo experiments. The synthesized nanoplatform with a combination of different features, including active nucleus‐targeting, high‐loading capacity, controlled release of cargo, and photothermal property, provides a new strategy for circumventing multidrug resistant cancers.     

Self‐Healing Graphene Oxide Based Functional Architectures Triggered by Moisture

Self‐healing materials are capable of spontaneously repairing themselves at damaging sites without additional adhesives. They are important functional materials with wide applications in actuators, shape memorizing materials, smart coatings, and medical treatments, etc. Herein, this study reports the self‐healing of graphene oxide (GO) functional architectures and devices with the assistance of moisture. These GO architectures can completely restore their mechanical‐performance (e.g., compressibility, flexibility, and strength) after healing their broken sites using a little amount of water moisture. On the basis of this effective moisture‐triggered self‐healing process, this study develops GO smart actuators (e.g., bendable actuator, biomimetic walker, rotatable fiber motor) and sensors with self‐healing ability. This work provides a new pathway for the development of self‐healing materials for their applications in multidimensional spaces and functional devices.     

Revisiting the Structure of Graphene Oxide for Preparing New‐Style Graphene‐Based Ultraviolet Absorbers

Despite sustained effort over the years, the exploration of an effective strategy toward understanding the structure and properties of graphene oxide (GO) is still highly desirable. Herein, a facile route to revisit the structure of GO is demonstrated by elucidating its chemical‐conversion process solely in the presence of ammonia. Such a strategy can contribute to settling some arguments in recent models of GO, and also offers a prerequisite to identify critical components that can act as ultraviolet absorbers (UVAs) in resulting dispersions of nitrogen‐doped graphene sheets (NGSs). Inspired by this, for the first time, the performance of NGSs, serving as new‐style UVAs, is investigated through directly assessing the effect of NGSs on the photofastness of azo dyes (Food Black). These studies reveal that, distinct from the common understanding, the as‐prepared NGSs can dramatically enhance the photostability of Food Black under UV irradiation and exhibit greatly applied potential as a multifunctional UVA for new‐generation inkjet inks that can simultaneously integrate the advantages of dye‐based and pigment‐based inks.     

Structure‐Based Enhanced Capacitance: In Situ Growth of Highly Ordered Polyaniline Nanorods on Reduced Graphene Oxide Patterns

A novel method is described for fabricating an all‐solid‐state flexible micro‐supercapacitor. The microelectrodes of the supercapacitor are prepared by in situ electrodeposition of polyaniline (PANI) nanorods on the surface of reduced graphene oxide (rGO) patterns that are fabricated by micromolding in capillaries. The morphologies of PANI nanorods could be controlled by the concentration of aniline and the growth time in the electrodeposition process. The micro‐supercapacitor possesses electrochemical capacitance as high as 970 F g^?1 at a discharge current density of 2.5 A g^?1, as well as good stability, retaining 90% of its initial capacitance after 1700 consecutive cycles for the synergistic effect of these new rGO/PANI nanostructures. The results show that the method could represent a route for translating the interesting fundamental properties of rGO and conducting polymers into technologically viable energy devices. Furthermore, this study might further guide the preparation of functional graphene‐based materials.     

Epoxide Speciation and Functional Group Distribution in Graphene Oxide Paper‐Like Materials

The electronic structure and chemical bonding of three differently prepared samples of graphene oxide paper‐like sheets are studied. Two are created by water filtration of fully oxidized graphene sheets, although one is later intercalated with dodecylamine. The third is created by reducing graphene oxide with hydrazine hydrate. The spectroscopic fingerprints of the aligned epoxide functional groups that unzip the carbon basal plane are found. This unzipping appears to be a result of aging, and the extent to which the basal plane is unzipped can be controlled via the preparation method. In particular, reduction with hydrazine enhances line defect formation, whereas intercalation inhibits the process.The hydroxyl functional group also has a tendency to gather in zones of dense oxidation on the carbon basal plane, a predilection that is not shared by the other prominent functional group species. Finally, the non‐functionalized carbon sites exhibit very similar bonding despite the increase in the sp²/sp³ ratio, confirming that reduction alone is insufficient for producing pristine graphene from graphene oxide. These results are obtained by directly probing the electronic structure of the graphene oxide samples via X‐ray absorption near‐edge structure spectroscopy (XANES) and resonant X‐ray emission spectroscopy (RXES). This work has important significance for the development of graphene oxide as a band gap‐engineered electronic material, as preparation methodology strongly affects not only the initial condition of the sample, but how the electronic structure evolves over time.     

Enhanced Physiochemical and Mechanical Performance of Chitosan‐Grafted Graphene Oxide for Superior Osteoinductivity

The regeneration of artificial bone substitutes is a potential strategy for repairing bone defects. However, the development of substitutes with appropriate osteoinductivity and physiochemical properties, such as water uptake and retention, mechanical properties, and biodegradation, remains challenging. Therefore, there is a motivation to develop new synthetic grafts that possess good biocompatibility, physiochemical properties, and osteoinductivity. Here, we fabricate a biocompatible scaffold through the covalent crosslinking of graphene oxide (GO) and carboxymethyl chitosan (CMC). The resulting GO‐CMC scaffold shows significant high water retention (44% water loss) compared with unmodified CMC scaffolds (120% water loss) due to a steric hindrance effect. The modulus and hardness of the GO‐CMC scaffold are 2.75‐ and 3.51‐fold higher, respectively, than those of the CMC scaffold. Furthermore, the osteoinductivity of the GO‐CMC scaffold is enhanced due to the π–π stacking interactions of the GO sheets, which result in striking upregulation of osteogenesis‐related genes, including osteopontin, bone sialoprotein, osterix, osteocalcin, and alkaline phosphatase. Finally, the GO‐CMC scaffold exhibits excellent reparative effects in repairing rat calvarial defects via the synergistic effects of GO and bone morphogenetic protein‐2. This study provides new insights for developing bone substitutes for tissue engineering and regenerative medicine.     

Direct Growth of Edge‐Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High‐Performance Microwave Absorption

High‐performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave‐transmitting matrices is of paramount importance to bring it to real‐world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge‐rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si₃N₄ ceramics using only methyl alcohol (CH₃OH) as precursor is reported. The large O/C atomic ratio of CH₃OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si₃N₄ hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide‐based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.