Graphene, an atomic-scale honeycomb crystal lattice, is increasingly becoming popular because of its excellent mechanical, electrical, chemical, and physical properties. However, its zero bandgap places restrictions on its applications in field-effect transistors (FETs). Graphene nanomesh (GNM), a new graphene nanostructure with a tunable bandgap, shows more excellent performance. It can be widely applied in electronic or photonic devices such as highly sensitive biosensors, new generation of spintronics and energy materials. These illustrate significant opportunities for the industrial use of GNM, and hence they push nanoscience and nanotechnology one step toward practical applications. This review briefly describes the current status of the design, synthesis, and potential applications of GNM. Finally, the perspectives and challenges of GNM development are presented and some suggestions are made for its further development and exploration.
In this work, a facile hydrothermal approach for the shape-controlled synthesis of NiCo2S4 architectures is reported. Four different morphologies, urchin-, tube-, flower-, and cubic-like NiCo2S4 microstructures, have been successfully synthesized by employing various solvents. The obtained precursors and products have been characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. It is revealed that the supersaturation of nucleation and crystal growth is determined by the solvent polarity and solubility, which can precisely control the morphology of NiCo2S4 microstructures. The detailed electrochemical performances of the various NiCo2S4 microstructures are investigated by cyclic voltammetry and galvanostatic charge-discharge measurements. The results indicate that the tube-like NiCo2S4 exhibits promising capacitive properties with high capacitance and excellent retention. Its specific capacitance can reach 1048 F g(-1) at the current density of 3.0 A g(-1) and 75.9% of its initial capacitance is maintained at the current density of 10.0 A g(-1) after 5000 charge-discharge cycles.
A facile and phase-controlled synthesis of ?-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of ?-NiS and preventing its transition to ?-phase, which is in strong contrast to large aggregated ?-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall ?-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740?F g(-1) at current densities of 1, 2, 5, 10?A g(-1), respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials.
Three-dimensional graphene foam (3DGF) is a superior sensing material because of its high conductivity, large specific surface area and wide electrochemical potential windows. In this work, hexagonal Ni(OH)2 nanosheets are deposited on the surface of chemical vapor deposition-grown 3DGF through a facial hydrothermal process without any auxiliary reagents. The morphology and structure of the composite are characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy, and X-ray diffraction (XRD). Based on the Ni(OH)2/3DGF composite, a free-standing electrochemical electrode is fabricated. Being employed as a nonenzymatic glucose detection electrochemical electrode, it exhibits a high sensitivity (?2.65 mA mM(-1) cm(-2)), low detection limit (0.34 ?M) and excellent selectivity with a linear response from 1 ?M to 1.17 mM. The excellent sensing properties of the Ni(OH)2/3DGF electrode may be attributed to the synergistic effect of the high electrocatalytic activity of Ni(OH)2 nanosheets and the high conductivity and large surface area of 3DGF.
Hierarchical mesoporous spinel NiCo?O? was synthesized by a facile hydrothermal method assisted by polyvinylpyrrolidone (PVP) and a post annealing treatment. The synthesized hierarchical mesoporous NiCo?O? presents a hierarchical mesoporous structure with diameters of 5.0 and 25 nm, respectively. Compared to conventional flower-like NiCo?O?, the hierarchical mesoporous structured NiCo?O? exhibits excellent supercapacitor performance. The specific capacitance can reach 1619.1 F g(-1) at a current density of 2.0 A g(-1). When the current density is increased to 10.0 A g(-1), a specific capacitance of 571.4 F g(-1) can be obtained. Furthermore, the hierarchical mesoporous structured NiCo?O? presents excellent stability. The outstanding electrochemical performance of the hierarchical mesoporous NiCo?O? reveals its potential to be a promising material for use in supercapacitors, and also inspires continued research on binary metal oxides as energy transformation materials.
Graphene, because of its excellent mechanical, electrical, chemical, physical properties, sparked great interest to develop and extend its applications. Particularly, graphene based field-effect transistors (GFETs) present exciting and bright prospects for sensing applications due to their greatly higher sensitivity and stronger selectivity. This Review highlights a selection of important topics pertinent to GFETs and their application in electronic sensors. This article begins with a description of the fabrications and characterizations of GFETs, and then introduces the new developments in physical, chemical, and biological electronic detection using GFETs. Finally, several perspective and current challenges of GFETs development are presented, and some proposals are suggested for further development and exploration.
In this work, graphene materials have been prepared via thermal treatment of graphene oxides with the aid of intercalated nitric acid. The nitric acid not only favors the expansion of graphene but also facilitates the generation of pores into graphene. The specific surface area of such graphene frameworks is as high as 463 m(2)/g, and the pore volume reaches up to 2.23 cm(3)/g. When tested as supercapacitor electrodes, the graphene frameworks delivered an extremely high specific capacitance of ?370 F/g while simultaneously maintained an excellent energy density of 12.9 Wh/kg and power delivery of 250 W/kg in aqueous electrolyte. These performances are much better than those of the control samples prepared without the aid of nitric acid. The porous structure and large specific surface area are believed to have contributed to the high performances.
Nanostructured Co3O4 materials attracted significant attention due to their exceptional electrochemical (pseudo-capacitive) properties. However, rigorous preparation conditions are needed to control the size (especially nanosize), morphology and size distribution of the products obtained by conventional methods. Herein, we describe a novel one step shape-controlled synthesis of uniform Co3O4 nanocubes with a size of 50 nm with the existence of mesoporous carbon nanorods (meso-CNRs). In this synthesis process, meso-CNRs not only act as a heat receiver to directly obtain Co3O4 eliminating the high-temperature post-calcination, but also control the morphology of the resulting Co3O4 to form nanocubes with uniform distribution. More strikingly, mesoporous Co3O4 nanocubes are obtained by further thermal treatment. The structure and morphology of the samples were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A possible formation mechanism of mesoporous Co3O4 nanocubes is proposed here. Electrochemical tests have revealed that the prepared mesoporous Co3O4 nanocubes demonstrate a remarkable performance in supercapacitor applications due to the porous structure, which endows fast ion and electron transfer.
The monolithic three-dimensional (3D) graphene network is used as the support for Pt nanoparticles (NPs) to fabricate an advanced 3D graphene-based electrocatalyst. Distinct from previous strategies, the monodispersed Pt NPs with ultrafine particle size (?3 nm) are synthesized using ferritin protein nanocages as the template and subsequently self-assembled on the 3D graphene by leveraging on the hydrophobic interaction between the ferritin and the graphene. Following the self-assembly, the ferritins are removed, resulting in a stable Pt NP/3D graphene composite. The composite exhibits much enhanced electrocatalytic activity for methanol oxidation as compared with both Pt NP/chemically reduced graphene oxide (Pt/r-GO) and state-of-the-art Pt/C catalyst. The observed electrocatalytic activity also shows marked improvement over Pt/3D graphene prepared by pulse electrodeposition of Pt. This study demonstrates that protein nanocage templating and assembly are promising strategies for the fabrication of functional composites in catalysis and fuel cell applications.
Owing to their extraordinary electrical, chemical, optical, mechanical and structural properties, graphene and its derivatives have stimulated exploding interests in their sensor applications ever since the first isolation of free-standing graphene sheets in year 2004. This article critically and comprehensively reviews the emerging graphene-based electrochemical sensors, electronic sensors, optical sensors, and nanopore sensors for biological or chemical detection. We emphasize on the underlying detection (or signal transduction) mechanisms, the unique roles and advantages of the used graphene materials. Properties and preparations of different graphene materials, their functionalizations are also comparatively discussed in view of sensor development. Finally, the perspective and current challenges of graphene sensors are outlined (312 references).
Graphene oxide nanoribbons (GONRs) have been prepared by chemically unzipping multiwalled carbon nanotubes (MWCNTs). Thin-film networks of GONRs were fabricated by spray-coating, followed by a chemical or thermal reduction to form reduced graphene oxide nanoribbons (rGONRs). Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) characterizations indicate that the thermal reduction in the presence of ethanol vapor effectively restores the graphitic structure of the GONR as compared to chemical reduction with hydrazine vapor. Electrical measurements under a liquid-gate configuration demonstrates that rGONR network field-effect transistors exhibit much higher on/off ratios than a network of microsized reduced graphene oxides (rGOs) or a continuous film of single-layered pristine or chemical vapor deposited (CVD) graphene. Furthermore, we demonstrated the potential applications of rGONR networks for biosensing, specifically, the real-time and sensitive detection of adenosine triphosphate (ATP) molecules.
In this work, we show that the maximum thermopower of few layers graphene (FLG) films could be greatly enhanced up to ?700 ?V/K after oxygen plasma treatment. The electrical conductivities of these plasma treated FLG films remain high, for example, ?10(4) S/m, which results in power factors as high as ?4.5 × 10(-3) W K(-2) m(-1). In comparison, the pristine FLG films show a maximum thermopower of ?80 ?V/K with an electrical conductivity of ?5 × 10(4) S/m. The proposed mechanism is due to generation of local disordered carbon that opens the band gap. Measured thermopowers of single-layer graphene (SLG) films and reduced graphene oxide (rGO) films were in the range of -40 to 50 and -10 to 20 ?V/K, respectively. However, such oxygen plasma treatment is not suitable for SLG and rGO films. The SLG films were easily destroyed during the treatment while the electrical conductivity of rGO films is too low.
Graphene, a single-atom-thick and two-dimensional carbon material, has attracted great attention recently. Because of its unique electrical, physical, and optical properties, graphene has great potential to be a novel alternative to carbon nanotubes in biosensing. We demonstrate the use of large-sized CVD grown graphene films configured as field-effect transistors for real-time biomolecular sensing. Glucose or glutamate molecules were detected by the conductance change of the graphene transistor as the molecules are oxidized by the specific redox enzyme (glucose oxidase or glutamic dehydrogenase) functionalized onto the graphene film. This study indicates that graphene is a promising candidate for the development of real-time nanoelectronic biosensors.
A novel electrochemical sensing system for direct electrochemistry-based hydrogen peroxide biosensor was developed that relied on the virtues of excellent biocompatibility, conductivity and high sensitivity to the local perturbations of single-layer graphene nanoplatelet (SLGnP). To demonstrate the concept, the horseradish peroxidase (HRP) enzyme was selected as a model to form the SLGnP-TPA (tetrasodium 1,3,6,8-pyrenetetrasulfonic acid)-HRP composite film. The single-layer graphene composite film displayed a pair of well-defined and good reversible cyclic voltammetric peak for Fe(III)/Fe(II) redox couple of HRP, reflecting the enhancement for the direct electron transfer between the enzyme and the electrode surface. Analysis using electrochemical impedance spectroscopy (EIS) revealed that electrostatic attractions existed between graphene monolayers and enzyme molecules. The intimate graphene and enzyme interaction was also observed using scanning electron microscopy (SEM), which resulted in the special properties of the composite film. Ultraviolet visible spectroscopy (UV-vis) indicated the enzyme in the composite film retained its secondary structure similar to the native state. The composite film demonstrated excellent electrochemical responses for the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)), thus suggesting its great potential applications in direct electrochemistry-based biosensors.
Graphene is a promising candidate for making next-generation nanoelectronic devices. Developing methods to produce large sized graphene with high yield is the key for graphene applications. Here, we report a simple method for large-scale production of ultra-large single-layer graphene sheet (up to 50 microm) reduced from graphene oxides by hydrazine in the presence of aromatic tetrasodium 1,3,6,8-pyrenetetrasulfonic acid (TPA) which efficiently disperse the resulting graphene sheet in aqueous solutions. Field-effect transistors can be readily fabricated using such large reduced graphene oxide sheets. It was found that the mobility of the reduced graphene oxide increases with the temperature of subsequent thermal reduction and reaches 3.5 cm(2) V(-1) s(-1) after reduction at 1000 degrees C. Such solution-processable method is of great potential in printable fabrication of graphene-based devices.
Type 2 diabetes is a complex disease that is marked by the dysfunction of glucose and lipid metabolism. Hepatic insulin resistance is especially pathogenic in type 2 diabetes, as it dysregulates fasting and postprandial glucose tolerance and promotes systemic dyslipidemia and nonalcoholic fatty liver disease. Mitochondrial dysfunction is closely associated with insulin resistance and might contribute to the progression of diabetes. Here we used previously generated mice with hepatic insulin resistance owing to the deletion of the genes encoding insulin receptor substrate-1 (Irs-1) and Irs-2 (referred to here as double-knockout (DKO) mice) to establish the molecular link between dysregulated insulin action and mitochondrial function. The expression of several forkhead box O1 (Foxo1) target genes increased in the DKO liver, including heme oxygenase-1 (Hmox1), which disrupts complex III and IV of the respiratory chain and lowers the NAD(+)/NADH ratio and ATP production. Although peroxisome proliferator-activated receptor-gamma coactivator-1alpha (Ppargc-1alpha) was also upregulated in DKO liver, it was acetylated and failed to promote compensatory mitochondrial biogenesis or function. Deletion of hepatic Foxo1 in DKO liver normalized the expression of Hmox1 and the NAD(+)/NADH ratio, reduced Ppargc-1alpha acetylation and restored mitochondrial oxidative metabolism and biogenesis. Thus, Foxo1 integrates insulin signaling with mitochondrial function, and inhibition of Foxo1 can improve hepatic metabolism during insulin resistance and the metabolic syndrome.
Aromatic molecules can effectively exfoliate graphite into graphene monolayers, and the resulting graphene monolayers sandwiched by the aromatic molecules exhibit a pronounced Raman G-band splitting, similar to that observed in single-walled carbon nanotubes. Raman measurements and calculations based on the force-constant model demonstrate that the absorbed aromatic molecules are responsible for the G-band splitting by removing the energy degeneracy of in-plane longitudinal and transverse optical phonons at the Gamma point.
A sense of cell-being: Single-walled carbon nanotubes (SWNTs) are functionalized with bioactive monosaccharides to enable their use as biosensors. The glycosylated nanotube network is biocompatible and can interface with living cells (see scheme) to electronically detect biomolecular release with high temporal resolution and high sensitivity.
Owing to its unique combination of electrical, physiochemical, and one-dimension structural properties, single-walled carbon nanotube (SWNT) has recently emerged as a novel nanoelectronic biosensor for biomolecular detection with extraordinary sensitivity and simple detection scheme. All the realizations so far, however, are limited to static in vitro measurement. Dynamic detection of biomolecule release from living cells which may occur in millisecond timescale has yet to be demonstrated. In the present work, SWNT network was utilized to directly interface with living neuroglial astrocytes and label-freely detect the triggered release of adenosine triphosphate (ATP) from these cells with high temporal resolution. The secreted ATP molecules diffuse into the narrow interface gap between the SWNT-net and the astrocyte, and interact with the nanotubes. Highly charged ATP molecules electrostatically modulate the SWNT conductance leading to measurable current response. This technique provides a novel platform to study ATP release and signaling which play important roles in astrocyte-neuron crosstalk and other essential cellular functions.
A monolithic 3D hybrid of graphene and carbon nanotube was synthesized by two-step chemical vapor deposition. Owing to its superhydrophobic and superoleophilic properties, it can selectively remove oils and organic solvents from water with high absorption capacity and good recyclability.
A novel graphene-cobalt oxide hybrid needle-like electrode was fabricated for non-enzymatic glucose detection. Taking advantage of its small size, the needle electrode can probe glucose in a micro-droplet with high sensitivity.
Graphene, a single-atom-thick monolayer of sp(2) carbon atoms perfectly arranged in a honeycomb lattice, is an emerging sensing material because of its extraordinary properties, such as exceptionally high specific surface area, electrical conductivity, and electrochemical potential window. In this study, we demonstrate that three-dimensional (3D), macroporous, highly conductive, and monolithic graphene foam synthesized by chemical vapor deposition represents a novel architecture for electrochemical electrodes. Being employed as an electrochemical sensor for detection of dopamine, 3D graphene electrode exhibits remarkable sensitivity (619.6 ?A mM(-1) cm(-2)) and lower detection limit (25 nM at a signal-to-noise ratio of 5.6), with linear response up to ?25 ?M. And the oxidation peak of dopamine can be easily distinguished from that of uric acid - a common interferent to dopamine detection. We envision that the graphene foam provides a promising platform for the development of electrochemical sensors as well as other applications, such as energy storage and conversion.
Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200 °C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO(3) solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H(2)O(2) reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by immobilization of glucose oxidase on the bimodal np-Au.
The morphologies/dimensions of Au nanostructures can be tailored by merely controlling the reduction degree of graphene oxide surface. Au nanoparticles, long Au nanowires, and semicircular-shaped Au nanoplates are in situ synthesized on slightly, moderately, and highly reduced graphene oxide films respectively, without the need of any templating agent.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.