Bare Graphene Research Articles

Metal loaded nano-carbon gas sensor array for pollutant detection * *Pr. A. Abdelghani dedicates this work to the memory of his Father, El Haj Amor ben Abdelghani, who passes away the 28th of July 2021 in Tunisia, may God grant him eternal rest.

Many research works report a sensitive detection of a wide variety of gas species. However, their in-lab detection is usually performed by using single gases and, therefore, selectivity often remains an unsolved issue. This paper reports a four-sensor array employing different nano-carbon sensitive layers (bare graphene, SnO2@Graphene, WO3@Graphene, and Au@CNTs). The different gas-sensitive films were characterised via several techniques such as FESEM, TEM, and Raman. First, an extensive study was performed to detect isolated NO2, CO2, and NH3 molecules, unravelling the sensing mechanism at the operating temperatures applied. Besides, the effect of the ambient moisture was also evaluated. Afterwards, a model for target gas identification and concentration prediction was developed. Indeed, the sensor array was used in mixtures of NO2 and CO2 for studying the cross-sensitivity and developing a calibration model. As a result, the NO2 detection with different background levels of CO2 was achieved with an R 2 of 0.987 and an RMSE of about 22 ppb.

Optogenetically engineered cell-based graphene transistor for pharmacodynamic evaluation of anticancer drugs

Rapid and effective cell-based pharmacodynamic evaluation in vitro is crucial for providing an experimental basis for the effectiveness and safety of drugs, and the existing cell-based methods for pharmacodynamics evaluation are usually invasive, dependent on chemical reagents, and/or unable to monitor the process in real time. Here, an optogenetically engineered cell-based graphene transistor is presented as a biosensor for the pharmacodynamic evaluation of anticancer drugs. The biosensor consists of a bare graphene transistor and optogenetically engineered cells as the gate terminal. The photoresponse of engineered cells regulates the output of the transistor and the increment pattern in the transistor output current upon drug action can be used to evaluate the drug efficacy. The results show that the optogenetic engineering of cancer cells does not affect the killing effect of drugs on the cells, and validate the effectiveness of the biosensor. The patterns of photoinduced increments exhibit significant variation with drug action time within 4 h or drug concentration in a range of 1 nM to 1 mM, and can qualitatively characterize the drug efficacy. Furthermore, the drug efficacy can be quantitatively evaluated with an indicator by logarithmically fitting the photoinduced increment patterns. The result also shows that the drain–source voltage significantly affects the evaluation performance and it is necessary to calibrate the voltage value to enhance the performance of the biosensor. The proposed biosensor affords simple, non-destructive, and time-efficient pharmacodynamic evaluation in vitro and is significant to understand the effect and mechanism of drugs in its early development stage.

Self-assembly synthesis of 3D graphene/nano-Fe3O4 hybrid aerogels with improved mechanical and thermal properties

Graphene aerogel and graphene-magnetite hybrid aerogel were prepared using hydrothermal method followed by a freeze-drying process. Magnetite nanoparticles were encapsulated by graphene sheets in an electrostatic self-assembly process. The morphology and properties of aerogels were characterized by several techniques including UV-Vis spectroscopy, Raman spectroscopy, FESEM, TEM and XRD. The mechanical and thermal behavior of the aerogels were evaluated at different concentration levels of Fe3O4 nanoparticles (0, 10, 20 and 30 wt%). The compressive strengths of the hybrid aerogels at the strain of 80% for graphene aerogels containing 0, 10, 20 and 30 wt% Fe3O4 nanoparticles were determined to be 5.93, 12.96, 6.85, and 6.15 kPa, respectively. The highest mechanical properties were achieved for the sample containing 10 wt% Fe3O4 nanoparticles (FGA10). Thermal analysis revealed that FGA10 sample had a 15% less weight loss when heated up to 600 °C compared with that for the bare graphene aerogel, indicating the formation of a more thermally stable structure. Furthermore, adding Fe3O4 nanoparticles improved the thermal insulation performance of the graphene aerogel, since the dynamic heat transfer rate and heat dissipation rate of FGA10 were lower than those for the bare graphene aerogel.

Reduction of metal nanoparticle decorated flexible graphene oxide by laser at various temperatures and under selected atmospheres

In situ Raman spectroscopy of flexible films of bare graphene oxide (GO) and GO decorated with Pt and Au nanoparticles (NPs) were examined upon exposure to synthetic air and 1% hydrogen in synthetic air. Initially, GO possesses an sp2 rich-structure at room temperature; however, it suffers from a drastic sp2 loss at higher temperatures under argon laser exposure leading to structural damage above 65 °C. Conversely, metal nano particle (MNP) decorated GO undergoes a drastic reduction of sp2 content mainly due to an increased defect density. In MNP composites, the formation rate of reduced graphene oxide (rGO) elevates at higher temperatures leading to an improvement in the sp2 fraction to some extent under argon laser exposure. In fact, the optical properties of MNP decorated GO drastically change against those of bare GO. Despite Pt NPs demonstrating a large catalytic effect with temperature, Au NPs do not. Similarly, the catalytic effect of Pt-GO gives rise to a slight excess in rGO formation in favor of the sp2 domain recovery. Here, there is a dominant temperature effect and a minor catalytic effect during laser exposure to GO.

Theoretical investigation of the NLO properties of a series of (C5N)n bare graphene nanoribbons

In this research, the electronic and chemical properties of a series of ( C5N)n nanoribbons have been investigated. The effect of nanoribbon length on the polarizability and hyperpolarizability of the molecules has been considered. It has been demonstrated that odd or even number of constructive units impresses on the polarizability of this type of nanoribbons. Clearly, ( C5N)2n nanoribbons show better NLO properties. To survey the chemical properties of considered nanoribbons, the frontier molecular orbitals have been studied. Aromaticity of involving rings in considered nanoribbons has been investigated, too.

Bloch Surface Wave‐Assisted Ultrafast All‐Optical Switching in Graphene

AbstractGraphene has ultrafast charge carrier dynamic and shows strong light–matter interaction allowing the use in photovoltaic devices, fast photodetectors, saturable absorbers, and electro‐optical modulators. However, despite the high nonlinear optical susceptibilities, the small amount of material significantly limits the use of graphene for nonlinear optical applications. In this work, Bloch surface waves (BSWs) are employed, enhancing the graphene–light interaction, for all‐optical switching realization. By placing a graphene monolayer on top of a 1D photonic crystal, it is shown that for the wavelength corresponding to the BSW resonance, the reflection coefficient is modulated on the sub‐picosecond time scale by an order of magnitude larger than that for bare graphene. The magnitude of the reflection change reaches 0.3% at the fluence of 40 µJ cm−2. The reported results are proof of priciple possibility of BSW‐assisted enhancing the reflection modulation of any 2D materials and transparent thin films while maintaining their inherent ultrafast dynamics, which is useful for the further development of all‐optical switches.

Surface Modifications in Graphene by DNA Aptamers for Staphylococcus Aureus Detection

Surface modifications with organic molecules comprise a versatile tool to enable applications of graphene in the field of biotechnology. In this context, interfacing graphene with ligands such as antibodies and aptamers constitutes a prevalent methodology for the realization of bioselective graphene surfaces. Following this concept, in this work, we describe two novel routes for surface modifications of graphene devices with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Staphylococcus aureus</i> aptamers (SA20), which render graphene surfaces specific for this bacterium. The first method makes use of amino-modified SA20 and the second approach involves SA20 aptamers featuring a pyrene moiety. Significantly, while the resulting aptamer-modified graphene devices exhibit an evident discrimination between the target ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Staphylococcus aureus</i> ) and control ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> ) bacteria, bare graphene transistors respond similarly to the addition of these distinct biological compounds. This reveals that both functionalization strategies successfully result in selective graphene surfaces, providing robust alternatives for construction of tailored graphene-based biosensors.

Theoretical Insights into the NH3 Decomposition Mechanism on the Cu- and Pt- Embedded Graphene Surfaces: A DFT Approach

Herein, the catalytic activities of Cu-and Pt-embedded graphene surfaces on the sequential decomposition reaction of NH3 molecule were investigated by density functional theory (DFT). Partial charge changes on the surfaces by embedding Cu and Pt atoms on the bare graphene surface were analyzed by the Bader charge analysis and depicted by the electron density difference maps. Grimme-D2 dispersion correction was employed for weak interactions between adsorbates and both graphene surfaces. The most stable geometries of the adsorption of NHx (x = 0 → 3) and H species and their fragmented co-adsorption structures on both graphene surfaces were obtained. The internal energy barrier calculations required for the sequential decomposition of NH3 on both graphene surfaces were calculated by the CINEB method and the results obtained for complete decomposition of NH3 were illustrated by relative energy diagram. The findings revealed that the decomposition of NH3 to NH2, NH, and N on the Cu-embedded graphene surface had relatively lower activation barriers of 1.52 eV, 0.72 eV, and 0.64 eV, respectively, compared to the Pt-embedded graphene surface. The Cu-embedded graphene surface was of high selectivity over the NH3 sequential decomposition reaction. This information may paw the way for different strategies for the development of Cu-based catalysts for NH3 decomposition.

High-Performance and Ultralow-Noise Two-Dimensional Heterostructure Field-Effect Transistors with One-Dimensional Electrical Contacts

Two-dimensional heterostructure field-effect transistors (2D-HFETs) with one-dimensional electrical contacts to atomically thin channels have recently shown great device performance, such as reduced contact resistance, leading to ballistic transport and enhanced carrier mobility. While a number of low-frequency noise studies exists on bare graphene devices supported on silicon dioxide gate insulators with surface contacts, such studies in heterostructure devices comprising epitaxial graphene on hexagonal boron nitride (hBN) with edge contacts are extremely limited. In this article, we present a systematic, temperature-dependent study of electrical transport and low-frequency noise in edge-contacted high-mobility HFET with a single atomic-layer graphene channel encapsulated by hBN and demonstrate ultralow noise with a Hooge parameter of ≈10–5. By combining measurements and modeling based on underlying microscopic scattering mechanisms caused by charge carriers and phonons, we directly correlate the high-performance, temperature-dependent transport behavior of this device with the noise characteristics. Our study provides a pathway towards engineering low-noise graphene-based high-performance 2D-FETs with one-dimensional edge contacts for applications such as digital electronics and chemical/biological sensing.

Sensitive and selective electrochemical detection of vanillin at graphene based poly (methyl orange) modified electrode

Vanillin (VN) is a flavouring substance commonly used in the food and pharmaceutical industry. The rampant use of VN has significant implications on human health. In this work, a sensitive and selective voltammetric sensor to detect VN in food essences and natural vanilla beans was elucidated using a poly(methyl orange) modified graphene paste electrode (PMOMGPE). The surface morphology of PMOMGPE and a bare graphene paste electrode (BGPE) was compared using field emission - scanning electron microscopy (FE-SEM) and electron transfer kinetics were analysed by Electrochemical impedance spectroscopy (EIS). The electrochemical activities of PMOMGPE and BGPE were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in 0.2 M phosphate buffer solution (PBS) of an optimum pH of 6.5 with an accumulation time of 20 s in a potential window of 0.2 V–1 V. Superior electrocatalytic activity was observed by PMOMGPE for the oxidation of VN, which is attributed to the high surface area and interactions between the polymer film and analyte. The VN sensor exhibited a low detection limit of 7.35 × 10−8 M by the DPV method and 20.19 × 10−8 M by the CV method. Various parameters like heterogeneous rate constant (ko = 1.7 × 10−5 cm s−1), number of electrons transferred (n = 2), and surface concentration (Γ = 0.8 nmol cm−2) were calculated. The selectivity of the prepared sensor for VN detection in the presence of common interferents such as metal ions and organic species was noteworthy. PMOMGPE was reliably used for the simultaneous analysis of VN along with indigo carmine (IC) and tartrazine (TZ). This facile VN sensor can be effectively used for real sample analysis, due to its simplicity and stability.

Graphene Loading with Polypyrrole Nanoparticles for Trace-Level Detection of Ammonia at Room Temperature.

The outstanding versatility of graphene for surface functionalization has been exploited by its decoration with synthesized polypyrrole (PPy) nanoparticles (NPs). A green, facile, and easily scalable for mass production nanocomposite development was proposed, and the resulting PPy@Graphene was implemented in chemoresistive gas sensors able to detect trace levels of ammonia (NH3) under room-temperature conditions. Gas exposure for 5 min revealed that the presence of nanoparticles decorating graphene entail greater sensitivity (13-fold) in comparison to the bare graphene performance. Noteworthy, excellent repeatability (0.7% of relative error) and a low limit of detection of 491 ppb were obtained, together with excellent long-term stability. Besides, an extensive material characterization was conducted, and vibration bands obtained via Raman spectroscopy confirmed the formation of PPy NPs, while X-ray spectroscopy (XPS) revealed the relative abundance of the different species, as polarons and bipolarons. Additionally, XPS analyses were conducted before and after NH3 exposure to assess the PPy aging and the changes induced in their physicochemical and electronic properties. Specifically, the gas sensor was tested during a 5-month period, demonstrating significant stability over time, since just a slight decrease (11%) in the responses was registered. In summary, the present work reports for the first time the use of PPy NPs decorating graphene for gas-sensing purposes, revealing promising properties for the development of unattended gas-sensing networks for monitoring air quality.

Frequency-dependent ultrasensitive terahertz dynamic modulation at the Dirac point on graphene-based metal and all-dielectric metamaterials

The development of terahertz (THz) technology is creating a demand for devices that can modulate THz beams. Here, we report the design and characterization of three THz modulators. One uses graphene and a metal-microstructure-integrated metamaterial, another uses a bare graphene film, and the third uses graphene-based all-dielectric metamaterials. Ultrasensitive dynamic THz modulation is achieved by shifting the quasi-Fermi level between the Dirac point, the conduction band, and the valence of graphene via continuous-wave optical illumination or bias voltages. When the Fermi level is close to the Dirac point, the modulation is ultrasensitive to the external stimuli. The modulation depth can reach the maximum value of 346% in the current public publication, breaking through the bottleneck of modulation inefficiency, and is expected to realize practical applications for the first time. For the range 0.2–2 THz, the modulation depth initially increases, then decreases. These results will enable potential designs for ultrasensitive THz devices.

Perovskite@Graphene Nanohybrids for Breath Analysis: A Proof-of-Concept

Nanohybrids comprising graphene loaded with perovskite nanocrystals have been demonstrated as a potential option for sensing applications. Specifically, their combination presents an interesting synergistic effect owing to greater sensitivity when bare graphene is decorated with perovskites. In addition, since the main drawback of perovskites is their instability towards ambient moisture, the hydrophobic properties of graphene can protect them, enabling their use for ambient monitoring, as previously reported. However not limited to this, the present work provides a proof-of-concept to likewise employ them in a potential application as breath analysis for the detection of health-related biomarkers. There is a growing demand for sensitive, non-invasive, miniaturized, and inexpensive devices able to detect specific gas molecules in human breath. Sensors gathering these requirements may be employed as a screening tool for reliable and fast detection of potential health issues. Moreover, perovskite@graphene nanohybrids present additional properties highly desirable as the capability to be operated at room temperature (i.e., reduced power consumption), reversible interaction with gases (i.e., reusability), and long-term stability. Within this perspective, the combination of both nanomaterials, perovskite nanocrystals and graphene, possibly includes the main requirements needed, being a promising option to be employed in the next generation of sensing devices.

Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate.

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10−7 M was detected with enhancement factor of 82 × 104. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.

Effects of Oxygen Cathode Substrates with Various Carbon Catalysts on the Discharge Capacity of Lithium-Oxygen Battery

Lithium-oxygen batteries have been considered strong candidates to supersede current rechargeable batteries especially lithium-ion batteries. Despite having tremendously high theoretical energy density, the practically achievable energy density is far from commercial application till date. The oxygen electrode is one of the major bottlenecks in maximizing the battery capacity. It is comprised of a porous structure (mainly carbon) with high surface area and sufficient reaction sites. High porosity facilitates lithium ion and oxygen mass transfer and results in high storage capacity for the insoluble discharge product during discharging. The cathode electrode is fabricated by coating a catalyst layer on a porous carbon substrate. The substrate, which contacts with oxygen channels, plays a vital role in mass transfer of oxygen from outside to the reaction sites. Therefore, it is important to select a substrate that does not clog with deposition of Li2O2 particles immediately after discharging begins and allows oxygen to reach the catalyst side for longer period of time.This study investigates the effects of oxygen electrode substrates with various coating materials on the discharge capacity of lithium-oxygen battery. For this purpose, we have compared the discharge capacity of plain carbon cloth, plain carbon paper and carbon cloth or carbon paper coated with carbon catalysts including Vulcan XC, Super P and Graphene Oxide. 1.5mg/cm2 (+/-0.3mg/ cm2) is used as catalyst loading. The electrolyte used in this study is 1M LiTFSI in TEGDME. PTFE (30wt%) is used as a binder. All experiments are conducted at room temperature with pure oxygen supply.With carbon cloth as a substrate, the discharge capacities obtained were 3 to 6 times higher (depending on the carbon catalysts coated) than the capacities obtained with carbon paper. The bare carbon cloth, Vulcan XC, Super P and Graphene oxide with carbon cloth as a substrate have discharge capacities of 0.11 mAh/mg, 13 mAh/mg, 6.8 mAh/mg, 1.5 mAh/mg respectively. On the other hand, the discharge capacities achieved with bare carbon paper, Vulcan XC, Super P and graphene oxide with carbon paper as substrate were 0.02 mAh/mg, 2.4 mAh/mg, 2.7 mAh/mg, 0.28 mAh/mg respectively. The results clearly indicate that the cathode with carbon cloth as a substrate yields significantly higher discharge capacity with all the coating materials as compared with the carbon paper. The different performances of two substrates can be attributed to their structure and pore size distribution. Carbon cloth is composed of flexible woven threads with longer lengths ( ̴ 30µm) and broader pore size distribution (5-200 µm) with peaks at 10, 70 and 100 µm. This type of structure is favorable in reducing tortuosity, enhancing mass transport of oxygen and lithium ion and improving ionic conductivity. On the other hand, the structure of carbon paper comprises of non-woven short carbon fibers ( ̴ 15µm) and smaller pore size distribution range (10-70 µm) with a peak at 50 µm. This renders poor transport of oxygen from outside to the reaction sites leading to lower discharge capacity.The primary function of coating materials is to increase surface area of cathode thereby providing more reaction sites and creating tri-phase boundaries for reaction to take place. These catalysts also have different pore size distributions and resistance to mass transfer. Therefore, various carbon catalysts used yield different discharge capacity with same substrate.

Interfacial Chemical Effects of Amorphous Zinc Oxide/Graphene.

Research on the preparation and performance of graphene composite materials has become a hotspot due to the excellent electrical and mechanical properties of graphene. Among such composite materials, zinc oxide/graphene (ZnO/graphene) composite films are an active research topic. Therefore, in this study, we used the vacuum thermal evaporation technique at different evaporation voltages to fabricate an amorphous ZnO/graphene composite film on a flexible polyethylene terephthalate (PET). The amorphous ZnO/graphene composite film inherited the great transparency of the graphene within the visible spectrum. Moreover, its electrical properties were better than those of pure ZnO but less than those of graphene, which is not consistent with the original theoretical research (wherein the performance of the composite films was better than that of ZnO film and slightly lower than that of graphene). For example, the bulk free charge carrier concentrations of the composite films (0.13, 1.36, and 0.47 × 1018 cm−3 corresponding to composite films with thicknesses of 40, 75, and 160 nm) were remarkably lower than that of the bare graphene (964 × 1018 cm−3) and better than that of the ZnO (0.10 × 1018 cm−3). The underlying mechanism for the abnormal electrical performance was further demonstrated by X-ray photoelectron spectroscopy (XPS) detection and first-principles calculations. The analysis found that chemical bonds were formed between the oxide (O) of amorphous ZnO and the carbon (C) of graphene and that the transfer of the π electrons was restricted by C=O and C-O-C bonds. Given the above, this study further clarifies the mechanism affecting the photoelectric properties of amorphous composite films.

New graphene oxide-phosphoramide nanocomposites as practical tools for biological applications including anti-bacteria, anti-fungi and anti-protein

This work presents the synthesize methods and applications of water-soluble and uniform “graphene oxide/ phosphoramide ligands” (GO/L) nanocomposites by a cursory approach without any need for additional reductants. They are potential to provide much better biological properties, as enzyme immobilization, anti-bacterial and antifungal activity, in comparison to that of bare graphene oxide (GO) and phosphoraimides. In the provided study, an in-depth research of three GO based membranes, in which GO acts as the bed for the phosphoramide ligands, is presented. It is also proved that interlayer D-spacing of these membranes is wider compared to that of GO. These compounds were characterized by different analytical methods such as IR and NMR spectrums, AFM, XRD analyses and UV–visible. Additionally, the immobilization mechanisms of Acetylcholinesterase enzyme (AChE) by the GO and its new derivatives, the effects of new compounds as anti-bacteria and anti-fungi tools on Gluconacetobacter xylinus(G.xylinus) bacteria (an environmental bacteria) and Yeast cells were studied. the results showed that the GO/ L films had more potency as biological tools compared to bare GO and phosphoramide ligands. In comparison to previous works, this study aimed to introduce facile methods to synthesize powerful compounds which are active in several biological areas, more importantly, these compounds are not only more environmentally friendly ones than many presented compounds, but also are more economical and time saving. Such investigations would rich the understanding of the GO-based membranes, and also empowers future rational designs for a variety of applications such as food industry and drug design.

Potential electromagnetic column treatment of heavy metal contaminated water using porous Gd2O3-doped graphene oxide nanocomposite: Characterization and surface interaction mechanisms

Water contamination by heavy metal is a global issue. Here, used a facile method to prepare a porous hybrid nanomaterial of magnetic Gd2O3-doped graphene oxide (GGO) for remediation of water contaminated with Cr(III) and Pb(II). The structure and surface morphology of GGO were well characterized using XRD, magnetic measurement, FT-IR, XPS, SEM, and TEM data. Its surface area is larger compared to bare graphene oxide (GO) and iron oxide-doped GO, and the active surface functional groups enhance its adsorptive ability. The performance of GGO is significantly influenced by the pH, adsorbent dosage, initial metal concentration, and rate-limiting kinetics on homogeneous surfaces. Gd2O3 doping enhanced the adsorption ability of GO, achieving the respective maximum capacities of 17.97 and 83.04 mg/g for Cr(III) and Pb(II) at 0.5 g/L GGO, pH 4.0, 298 K, and 180 min. When GGO was applied to real water samples, the adsorptive removal rate satisfied the US EPA standards, and the material can be reused up to 3 cycles with more than 95 % and 70 % removal for Cr(III) and Pb(II), respectively. Therefore, GGO can be used for the potential removal of anions and cations from wastewater, including industrial effluents and groundwater.

Mechanism of transition metal interaction with graphene sheet reflected in its plasmonic excitations: Effect of gas adsorption phenomena studied by a combination of solid state and molecular orbital approaches

In this study, plasmonic properties of transition metal atoms (Sc-Zn, Pd, Pt) adsorbed on various sites of graphene sheets were investigated before and after CO adsorption by density functional theory (DFT). To this aim, Electron Energy Loss Spectroscopy (EELS) of these systems were obtained by periodic DFT. The results indicated that the highest in-plane plasmon peaks undergo blue shifts after CO adsorption, in such a way that Co–graphene system demonstrates the highest blue shift of 2.42 eV from Visible to UV region. Also, out-of-plane plasmons do not exhibit significant sensitivity to CO adsorption. For deeper understanding of electronic structure of metal-graphene systems, appropriate molecular models were considered, and natural bond orbital (NBO) analysis applied. Comparison of solid-state net charges with the NBO charges showed that CO adsorption has more non-local characteristics, while the metal atom adsorption on bare graphene surface has more local nature. Moreover, Jahn–Teller distortion of metal adatom strongly depends on the net charges of nearest-neighbor C atoms on the surface. In addition, spin distribution on metal 3d orbitals plays a role to some extent. These results can be useful for experimental researchers who want to construct the sensors and optical devices based on metal-graphene interactions.

A three component-based van der Waals surface vertically designed for biomolecular recognition enhancement

Graphene-based vertical electrodes may have applications in biomolecular recognition for producing low-cost biodevices with high electronic conductivity. However, they are unsuitable for measuring small interfacial capacitance variations because graphene is mostly composed of basal sp2 carbon surface, which limits its sensitivity as an electrochemical biosensor. Herein, we introduce a monolayer graphene based three-component vertically designed (TCVD) device composed of ferrocene adsorbed on monolayer graphene supported on lithographically designed gold subsurface on silicon wafer. Ferrocene is the top layer that promotes reversible redox communication with the electrolyte, while graphene–gold is the strategically projected layer underneath. This system exhibits an enhanced chemical reactivity by allowing the electrochemical attachment of the larger amount of the organic functional groups on its surface and faster electrochemical response to an inner-sphere redox probe in the solution. Bader charge analysis indicated that gold donates electronic density to the graphene surface, thereby significantly increases the charge transfer exchange rate with ferrocene. Based on density functional theory (DFT) simulation and spectromicroscopy data, it was realized that the interaction between gold and graphene is through physical adsorption with a slight change in the Fermi's level of graphene. The TCVD device was used to detect the adsorption of double-stranded DNA and DNA hybridization in solutions. Based on capacitance calculation measurements, DNA hybridization in nanomolar range with sensitivity four times higher and limit of detection (LOD) three times lower as compared to Fc/Gr/SiO2/Si, which was effortlessly detected. This result is promising since 3.0 µF cm−2 is the limit of quantum capacitance for bare graphene. Notably, these results open a new possibility for next-generation TCVD bioelectronics based on van der Waals surfaces, while further innovation and material scrutiny may lead to the achievement of TCVD devices with robust biomolecular recognition abilities.