Graphene Surface Research Articles

Facile and in situ production of reduced graphene oxide nanosheets paste electrode via electrochemical exfoliation of carbon paste electrode for fabricating a VEGF165 tumor marker aptasensor

The sensitive detection of trace amounts of vascular endothelial growth factor (VEGF165) in samples holds significant potential for clinical cancer diagnosis across various cancer types. This work introduces a simple, quick, and economical electrochemical method for exfoliating a graphite paste electrode (CPE) to directly synthesize a reduced graphene oxide nanosheet paste electrode (r-GONPE) for the determination of VEGF165. Thionine (Th) was used as a redox probe due to its strong interaction with the graphene surface. The functionalization of r-GONPE by thionine improves its stability while preserving the intrinsic properties of r-GONPE. Au nanoparticles were electrodeposited on the r-GONPE/Th electrode to stabilize the SH-aptamer by self-assembly for selective interaction and to enhance the speed of electron transfer. FESEM images confirmed the formation of a fixed, stable, very thin, and large few-layer reduced graphene oxide nanosheet on the outer surface of the CPE. The surface area of the bare CPE increased significantly after electrochemical exfoliation of the surface graphite layers (from 0.059 cm2 for CPE to 0.281 cm2 for r-GONPE). Electrical characterization showed that the conversion of graphite to graphene resulted in a five-fold increase in peak height and a decrease in peak separation by nearly 30 mV. The selective interaction of the VEGF165 with the r-GONPE/Th/nano-Au electrode modified with SH-aptamer reduced the oxidation peak current of thionine in the DPV signal. Thus, a wide linear calibration ranges from 5.0 pM to 320 pM and a low LOD of 1.03 pM (using the 3σ/S equation) were obtained. The aptasensor demonstrated consistent stability and strong selectivity against typical interferences when detecting picomolar concentrations of VEGF165. It also showed high accuracy and speed in detecting VEGF165 in human serum samples. Additionally, this aptasensor is advantageous due to its cost-effectiveness and simple fabrication process compared to traditional methods that use complex nanocomposites for signal enhancement.

Cu-Ag nanoparticles-dispersed and microchannel textured-laser induced graphene: A chemiresistive aptasensor for thrombin

Thrombin is a key enzyme of the clotting cascade, which can convert soluble fibrinogen to insoluble fibrin. A rapid and accurate sensor is required to give easy access to patients and healthy individuals to monitor their thrombin levels. In this study, a Cu and Ag bimetal nanoparticles (NPs)-dispersed and microchannel textured-laser induced graphene (Cu-Ag-LIG)-based chemiresistive aptasensor is developed. The sensor substrate was synthesized via the suspension polymerization of phenol and formaldehyde, with the in situ inclusion of the metal salts in the reaction mixture. Laser ablation converted the carbon containing polymeric groups to sp2 hybridized graphitic carbon and the metal salts to zero-valent metal NPs. Laser ablation was also used to create microchannels on the graphene surface to ensure the uniform distribution of the analyte. Ag NPs facilitated the binding of thrombin binding aptamer (TBA) via covalent bond, while Cu NPs provided structural support. The aptasensor showed a linear response over the 0.1–50 units/mL-thrombin concentration range. The sensor response was unaffected by common interfering biomolecules such as glucose, bovine serum albumin, urea, trypsin, and cholesterol. This study showcases the broader and often overlooked significance of chemiresistive sensors not only in healthcare but also across various scientific domains, offering avenues for transformative advancements in diagnostic technologies.

Simulation Study on Diffusion and Local Structure of CH4, CO2, SO2, and H2O Mixtures into Double-Layers Graphene.

Graphene has been widely studied as an ideal material for the adsorption and separation. In this work, we used molecular dynamics simulations to investigate the evolution of diffusion and local structure of CH4, CO2, SO2, and H2O mixtures into double-layers graphene under seven different interlayer spacings and four different CO2 concentrations. The results showed that the adsorption of CH4 and CO2 molecules on the graphene surface weakened with increased interlayer spacing. The diffusion capacities of CH4 and CO2 in the mixed system were significantly improved by increasing the interlayer spacing. In interlayer spacings ranging from 5 to 10 nm, the diffusion capacities of each component varied significantly in the order CH4 > CO2 ≫ H2O > SO2. Compared with CH4 and CO2, the local structures of SO2 and H2O were more affected by the interlayer spacing. Larger interlayer spacings or higher CO2 concentrations were advantageous for the formation of stronger hydrogen bond structures between H2O molecules. When the CO2 concentrations were between 10% and 20% and the interlayer spacing of graphene was 8 nm, the graphene structure exhibited the best adsorption and separation effects on CH4 and other components.

Electron Transport and Ion Diffusion in Hydrogen-Bonded Interlayer Cross-Linked Graphene/MXene for Wearable Micro-Sensors.

2D graphene and MXene have attracted much attention in the field of energy storage devices and wearable sensors due to their excellent electrical conductivity and mechanical properties. However, the capacitance of their composites is limited by low electron transport and sluggish ion diffusion due to the lack of electron transport and ion diffusion channels between stacked interlayers. Herein, this work reports the possibility of using disodium terephthalate as an auxiliary conductive bridge to cross-link the interlayer interaction between graphene and MXene from theoretical analysis and experimental verification. The cross-linker with a dicarboxyl group and a conjugated structure forms hydrogen bonds with the hydroxyl groups on the surface of graphene and MXene to provide a pathway for interlayer electron transfer, while inhibiting interlayer stacking and ensuring an effective ion diffusion process. To verify the actual effect of this approach, micro-sensors are assembled by the integration of micro-supercapacitors. The assembled micro-sensors demonstrate real-time monitoring of body movements and temperature signals. This work provides a feasible strategy to promote electron transport and ion diffusion in layered composites to design next-generation multifunctional micro-devices.

Laser-Driven Modular Precision Chemistry of Graphene Using λ3-Iodanes.

The emerging laser writing represents an efficient and promising strategy for covalent two dimensional (2D)-patterning of graphene yet remains a challenging task due to the lack of applicable reagents. Here, we report a versatile approach for covalent laser patterning of graphene using a family of trivalent organic iodine compounds as effective reagents, allowing for the engraving of a library of functionalities onto the graphene surface. The relatively weak iodine-centered bonds within these compounds can readily undergo laser-induced cleavage to in situ generate radicals localized to the irradiated regions for graphene binding, thus completing the covalent 2D-structuring of this 2D-film. The tailor-made attachment of distinct functional moieties with varying electrical properties as well as their thermally reversible binding manner enables programming the surface properties of graphene. With this delicate strategy the bottleneck of a limited scope of functional groups patterned onto the graphene surface upon laser writing is tackled.

Interfacial Electric Field Enhanced Free-Standing VO2/rGO Aerogel Anode with Ultra High Mass Energy Density for Aqueous Ammonium Ion Battery.

Aqueous batteries have become a promising means of energy storage due to its environmental friendliness. Nevertheless, it often exhibits limited energy density that hinder their application. Considering that ammonium ion (NH4 +) has a low mass and a small hydration radius, aqueous ammonium ion batteries (AAIBs) are expected to solve the problem of low energy density. Herein, we obtain Vanadium dioxide/reduced graphene oxide aerogel (VOGA) by in-situ growth of VO2 on the graphene surface for interfacial electric field enhanced AAIBs to achieve high mass energy density. The VOGA free-standing electrode achieves a specific capacity of up to 655 mAg-1 at a current density of 0.5 Ag-1. And the mass energy density of the VOGA.

Global Optimization of Molybdenum Subnanoclusters on Graphene: A Consistent Approach toward Catalytic Applications.

The development of novel subnanometer clusters (SNCs) catalysts with superior catalytic performance depends on the precise control of clusters' atomistic sizes, shapes, and accurate deposition onto surfaces. The intrinsic complexity of the adsorption process complicates the ability to achieve an atomistic understanding of the most relevant structure-reactivity relationships hampering the rational design of novel catalytic materials. In most cases, existing computational approaches rely on just a few structures to draw conclusions on clusters' reactivity thereby neglecting the complexity of the existing energy landscapes thus leading to insufficient sampling and, most likely, unreliable predictions. Moreover, modeling of the actual experimental procedure that is responsible for the deposition of SNCs on surfaces is often not done even though in some cases this procedure may enhance the significance of certain (e.g., metastable) adsorption geometries. This study proposes a novel systematic approach that utilizes global search techniques, specifically, the particle swarm optimization (PSO) method, in conjunction with ab initio calculations, to simulate all stages in the beam experiments, from predicting the most relevant SNCs structures in the beam and on a surface, to their reactivity. To illustrate the main steps of our approach, we consider the deposition of Molybdenum SNC of 6 Mo atoms on a free-standing graphene surface, as well as their catalytic properties with respect to the CO molecule dissociation reaction. Even though our calculations are not exhaustive and serve only to produce an illustration of the method, they are still able to provide insight into the complicated energy landscape of Mo SNCs on graphene demonstrating the catalytic activity of Mo SNCs and the importance of performing statistical sampling of available configurations. This study establishes a reliable procedure for performing theoretical rational design predictions.

Weakly negative permittivity from three-dimensional printed polydimethylsiloxane/graphene films in the radio frequency band

Epsilon-negative materials (ENMs) has become a research hotspot due to their unique physical properties and practical applications in fields such as directional radiation and tunneling effects. In this work, weakly negative permittivity (from -50 at 10 kHz to -25 at 1 MHz) was realized from three-dimensional printed polydimethylsiloxane/graphene films. The dielectric properties including complex permittivity (ε', ε″), complex impedance (Z', Z″), alternating current conductivity (σac), and dielectric loss tangent (tanδ) were investigated. When graphene content reached 15 wt%, the interconnected graphene network was formed, resulting in negative permittivity. Theory calculations were further used to explore the mechanism. The electrons around carbon atoms showed significant delocalization. With the effect of the external electromagnetic field, the electrons on the surface of graphene could easily oscillate collectively, leading to negative permittivity. Differential charge density exhibited that interfacial electric fields were formed between polydimethylsiloxane and graphene, enhancing positive permittivity. Therefore, when the graphene content reached 15 wt%, the film exhibited weakly negative permittivity, which was the result of the mutual balance between the graphene conductive network and the interface electric fields.

Electrically tunable graded photonic crystal lens based on graphene plasmons.

Controlling the nonlinear relationship between surface plasmon polariton (SPP) mode index and chemical potential of graphene can be used in the field of active transformation optics. Here, we propose an electrically tunable 2D Graded Photonic Crystal (GPC) lens based on graphene SPP platform. Our platform comprises a graphene monolayer integrated into a back-gated structure with nano-patterned gate insulators. When the chemical potential of the graphene surface is designed to operate in the nonlinear region, the designed GPC lens can be continuously transformed between a Maxwell's fish-eye lens and a Luneburg lens by tuning the gate voltage. The range of the lens background chemical potential for allowing this transformation is systematically studied. To compensate for the significant errors inherent in the conventional effective medium theory (EMT) during the homogenization of photonic crystals (PCs), we propose a generalized effective medium theory (GEMT). The validity and accuracy of this approach are verified through comparisons with true values (based on rigorous eigenvalue solutions) and EMT values. Due to its advantages of on-site controls and easy fabrication characteristics, the proposed graphene GPC provides a new way for practical on-chip light manipulation.

Numerical Verification of a Polarization-Insensitive Electrically Tunable Far Infrared Band-Stop Meta-Surface Filter

Tunable filters have many potential applications in diverse fields, including high-capacity communications, dynamic beam shaping and spectral imaging. Although providing a high-performance solution for actively tunable devices, metasurface combined with tunable materials faces the great challenges of limited tuning range and modulation depth. Here, we propose a far-infrared tunable band-stop filter based on Fabry-Perot (FP) resonators and graphene surface plasmons. By switching the wavelength of the critical coupling condition of the filter via the gate voltage applied on graphene, achieving the dynamically tunable band-stop filtering at the central wavelengths from 12.4 μm to 14.1 μm with a modulation depth of more than 99%. Due to the symmetry of the proposed meta-atoms, the filter is insensitive to the polarization direction of the incident light. And it can realize more than 85% filtering efficiency within 60° angle of incidence around the vertical direction. By adjusting the geometry of the meta-atoms structure, it is feasible to move the operational range from the near-infrared to terahertz bands.

Microwave‐assisted control of PtNi nanoalloy clusters on the nitrogen‐doped graphene oxide for energy conversion with oxygen reduction reaction and hydrogen evolution reaction

AbstractResearch on the production and utilization of hydrogen energy is essential to overcome the environmental issues caused by fossil fuels. Herein, we anchor PtNi nanoalloy clusters (Pt‐Ni NACs) on nitrogen‐doped graphene oxide (NrGO) by a facile microwave‐assisted synthesis and analyze the variations of catalyst properties based on the PtNi composition and the presence of nitrogen. Ni inclusion in the Pt matrix can induce lattice strain and change the electronic structure, while the doped nitrogen into the graphene can enhance electron transfer and improve the durability of the catalyst through strong chemical bonding with the alloy clusters. TEM analysis discovers that the NACs are uniformly decorated in a few‐nanometer‐size on the graphene surface, and the formation of the PtNi NACs and structural changes according to composition are confirmed through XRD and XPS. In addition, the structural changes due to N‐doping and its bonding with the NACs are observed through Raman spectroscopy and XPS. Electrochemical measurements reveal that Pt2.6Ni NACs/NrGO exhibits the highest ORR onset potential (0.893 V) and the lowest HER overpotential at 10 mA cm−2 (22 mV) among other catalysts, and those activities are almost unchanged under long‐term durability tests. From these results, Pt2.6Ni NACs/NrGO is utilized in a zinc‐air battery (ZAB) system, demonstrating better battery performance than commercial Pt and Ir‐based catalysts. Moreover, it is applied to hydrogen collection, showing linear trend in hydrogen production over time, confirming the catalyst's availability in hydrogen production and utilization.image

Plasmonic modulators based on enhanced interaction between graphene and localized transverse-electric plasmonic mode

Active plasmonic modulators with high modulation depth, low energy consumption, ultra-fast speed, and small footprint are of interest and particular significance for nanophotonics and integrated optics. Here by constructing a transverse-electric (TE) plasmonic mode and maximizing the in-plane component localized on the graphene surface, we propose a high-performing plasmonic modulator based on a graphene/split ring-like plasmonic waveguide (SRPW) system with a record high modulation depth (20.46 dB/µm) and suppressed insertion loss (0.248 dB/µm) at telecom wavelength 1310 nm, simultaneously possessing pronounced advantage in broadband ability (800-1650 nm) and superior electrical performance with energy consumption of 0.43 fJ/bit and modulation speed of 200 GHz. This innovative design provides a novel approach and idea for enhancing the interaction between light and matter in the waveguide system and will certainly inspire new schemes for the development of on-chip integrated optoelectronic devices.

An innovative strategy for Gefitinib quantification in pharmaceutical and plasma samples using a graphene quantum dots-combined gold nanoparticles composite electrochemical sensor.

Aninnovative methodology is proposedfor quantifying Gefitinib(GFT) using an electrochemical sensor constructed from a composite of graphene quantum dots (GQDs) and gold nanoparticles (AuNPs). GQDs were synthesized from graphite, preserving graphene's large surface area and excellent electron transfer capabilities while enhancing dispersibility. The combination of GQDs with AuNPs resulted in an AuNPs@GQDs composite, which was used to construct the sensor. The synthesized nanomaterials were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the electrochemical performance of the sensor was evaluated via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimized conditions, the sensor displayed a linear calibration curve for GFT detection within the range 0.01 to 10.0 µM, with a limit of detection (LOD) of 0.005 µM (S/N = 3). The sensor demonstrated excellent anti-interference properties and stability in tests using pharmaceutical formulations and plasma samples. Compared to chromatographic methods, the sensor exhibited similaraccuracy and recovery. Its easy fabrication and high sensitivity make it a promising tool for pharmaceutical analysis and clinical therapeutic drug monitoring.

Graphene reinforced magnesium metal matrix composites by infiltrating coated-graphene preform with melt

Graphene’s exceptional mechanical, electrical, and thermal conductivity capabilities make it an ideal reinforcement for metal matrix composites. However, graphene is hard to be dispersed in the melt metal due to its high surface energy, non-wetting nature, and strong van der Waals interactions between graphene sheets, which weaken the reinforcing efficiency of composites. A novel process by infiltrating the coated-graphene preform with melt magnesium was proposed to improve the dispersion of graphene in the magnesium matrix. Graphene preforms with oriented pores were prepared by a directional freeze-drying method. Magnesium oxide coatings were deposited on the surface of graphene inside the graphene preform using the evaporation of magnesium atoms to enhance the strength as well as the wettability between the preform and magnesium matrix. Magnesium matrix composites were fabricated by liquid-solid pressure infiltrating coated-graphene preform with molten magnesium. The microstructure of graphene preforms and composites and mechanical properties of the composites were characterized. The results show that graphene is uniformly dispersed in the matrix and presents a reticular structure, and the hardness, elastic modulus, and compressive strength of the composite were improved apparently compared to the matrix. This study suggests that the method of preparing composites by infiltration provides a novel strategy for fabricating nano-material reinforced magnesium matrix composites.

Giant Enhancement of Negative Friction by Resonant Coupling Between Localized Surface Phonon Polaritons and Graphene Plasmonics

Abstract Negative friction refers to a frictional force that acts in the same direction as the motion of an object, which has been predicted in terahertz (THz) gain systems [Phys. Rev. B 108 (4), 045406(2023)]. In this work, we investigate the enhancement of the negative friction experienced by nanospheres placed near a graphene substrate. We find that the magnitude of negative friction is related to the resonant coupling between the surface plasmon polaritons (SPPs) of the graphene and localized surface phonon-polaritons (LSPhP) of nanospheres. We exam nanospheres consisted of several different materials, including SiO2, SiC, ZnSe, NaCl, lnSb. Our results suggest that the LSPhP of NaCl nanospheres match effectively with the amplified SPPs of graphene sheets. The negative friction for NaCl nanospheres can be enhanced about one-to-two orders of magnitude compared to that of silica (SiO2) nanospheres. At the resonant peak of negative friction, the required quasi-Fermi energy of graphene is lower for NaCl nanospheres. Our finds hold great prospects for the mechanical manipulations of nanoscale particles.

Network of artificial olfactory receptors for spatiotemporal monitoring of toxic gas.

Excessive human exposure to toxic gases can lead to chronic lung and cardiovascular diseases. Thus, precise in situ monitoring of toxic gases in the atmosphere is crucial. Here, we present an artificial olfactory system for spatiotemporal recognition of NO2 gas flow by integrating a network of chemical receptors with a near-sensor computing. The artificial olfactory receptor features nano-islands of metal-based catalysts that cover the graphene surface on the heterostructure of an AlGaN/GaN two-dimensional electron gas (2DEG) channel. Catalytically dissociated NO2 molecules bind to graphene, thereby modulating the conductivity of the 2DEG channel. For the energy/resource-efficient gas flow monitoring, trust-region Bayesian optimization algorithm allocates many sensors optimally in a complex space. Integrated artificial neural networks on a compact microprocessor with a network of sensors provide in situ gas flow predictions. This system enhances protective measures against toxic environments through spatiotemporal monitoring of toxic gases.

A broadband tunable THz sensor based on graphene metasurface

In this paper, we design a polarization-independent and angle-insensitive wideband THz graphene metamaterial sensor. The proposed metasurface sensor consists of six layers, which are silicon dioxide substrate, metal reflector, air layer, graphene metasurface with microstructure, ion-gel layer and silicon dioxide dielectric layer from bottom to top. The sensor was simulated by using CST Microwave Studio software, and the absorption and sensing performance were analyzed. The results show that the absorption rate is more than 95 % in the range of 1.05–4.07 THz. In addition, when the Fermi energy level of graphene is changed, the absorption rate can be adjusted from 20 % to more than 95 %. At the same time, the absorptivity of the device can be maintained above 80 % before 60° when the TE and TM waves are incident, and it is insensitive to the polarization angle due to the central symmetry of the graphene surface microstructure. By changing the thickness of the air layer, the device can achieve maximum absorption at h2=30μm, where the maximum frequency shift sensitivity is 2.179 THz/RIU. The influence of structure parameters and incident angle on the absorption spectrum shows that the proposed structure has good stability. The proposed metasurface sensor has potential application prospects in biological detection and medical monitoring, broadening the application range of THz functional devices.

Synthesis of perylene‐PEO hyperdispersants for aqueous graphene dispersion

AbstractGraphene, with excellent thermal conductivity, electrical and corrosion shielding performance has great application potential in the fields of heat dissipation coating, conductive agent and anticorrosion composite coatings. However, due to its large specific surface area, resulting strong aggregation behavior limits its application. Herein, the hyperdispersants with perylene anchoring groups are synthesized through the amidation coupling reaction between diacid anhydride and polyetheramine. The branching degree and length of hydrophilic chains on hyperdispersant are revealed to be the very important factors to affect the dispersion stability of aqueous graphene dispersion. The hyperdispersant with a single hydrophilic chain and the molecular weight 2000 of polyetheramine has the excellent dispersal activity discovered by Rheology, particle size distribution and Raman measurements. The possible mechanism is the strongest anchoring effect of perylene on graphene surface and thus achieving in best effective spatial exclusion stabilization effect of hydrophilic chains.

Silicon–carbon superhydrophobic nano-structure for next generation semiconductor industry

Abstract Superhydrophobic surfaces are important in waterproof applications that withstand harsh chemical exposure, ultraviolet radiation, and heat. Surface energy modification of the surface, such as silanization or (fluoro)polymer coatings, increases the hydrophobicity of the nanostructure. The present study follows a bilayer architecture that turns hydrophilic silicon into a superhydrophobic one. The first step creates a unique silicon–graphene hybrid structure on the silicon surface by coating graphene on the P-type silicon substrate. In the second step, low surface energy material (a combination of hexadecyltrimethoxysilane and hexamethyldisilazane) is coated by the dip coating process. This study investigates the durability of superhydrophobicity under severe mechanical, thermal, and chemical conditions. High-temperature tolerance and water jet tests are also performed. The present work also involves the study of coating regeneration. This approach can be applied to all shapes and sizes of silicon–graphene surfaces and is proven to be excellent in the semiconductor industry.

Design and Analysis of a Highly Sensitive Terahertz Biosensor Using Graphene Metasurfaces and Surface Plasmon Resonance for Protein Detection with AI-Assisted Locally Weighted Linear Regression for Behavior Prediction

Design and Analysis of a Highly Sensitive Terahertz Biosensor Using Graphene Metasurfaces and Surface Plasmon Resonance for Protein Detection with AI-Assisted Locally Weighted Linear Regression for Behavior Prediction