Graphene Chip Research Articles

Temperature-induced activation and reversal of the relativistic ratchet currents on a graphene chip model

We investigate a monolayer graphene chip’s relativistic ratchet current (RRC). Our findings indicate that thermal noise can paradoxically amplify the RRC, in contrast to its conventional inhibitory role. Under noise, temperature (T) activation of the RRC remains stable over a broader range of T values, and an increased number of RRCs reversals are observed as a function of T and relevant parameters of the external electric field. The results regarding structural changes and symmetry breaking of the dissipative attractors can be understood. The observed activation and reversal of RRCs under a variation of external parameters unveil the diverse and complex behavior of the charge carrier transport on the graphene chip. Understanding this behavior allows for generating specific RRCs values, properties and effects for the charge carriers, offering a variety of possibilities for application and control of the graphene chip device.

Integrated Approach from Sample-to-Answer for Grapevine Varietal Identification on a Portable Graphene Sensor Chip.

Identifying grape varieties in wine, related products, and raw materials is of great interest for enology and to ensure its authenticity. However, these matrices' complexity and low DNA content make this analysis particularly challenging. Integrating DNA analysis with 2D materials, such as graphene, offers an advantageous pathway toward ultrasensitive DNA detection. Here, we show that monolayer graphene provides an optimal test bed for nucleic acid detection with single-base resolution. Graphene's ultrathinness creates a large surface area with quantum confinement in the perpendicular direction that, upon functionalization, provides multiple sites for DNA immobilization and efficient detection. Its highly conjugated electronic structure, high carrier mobility, zero-energy band gap with the associated gating effect, and chemical inertness explain graphene's superior performance. For the first time, we present a DNA-based analytic tool for grapevine varietal discrimination using an integrated portable biosensor based on a monolayer graphene field-effect transistor array. The system comprises a wafer-scale fabricated graphene chip operated under liquid gating and connected to a miniaturized electronic readout. The platform can distinguish closely related grapevine varieties, thanks to specific DNA probes immobilized on the sensor, demonstrating high specificity even for discriminating single-nucleotide polymorphisms, which is hard to achieve with a classical end-point polymerase chain reaction or quantitative polymerase chain reaction. The sensor was operated in ultralow DNA concentrations, with a dynamic range of 1 aM to 0.1 nM and an attomolar detection limit of ∼0.19 aM. The reported biosensor provides a promising way toward developing decentralized analytical tools for tracking wine authenticity at different points of the food value chain, enabling data transmission and contributing to the digitalization of the agro-food industry.

Polarization-independent plasmon-induced transparency and slow light effects in a fully continuous symmetric cross-shaped monolayer graphene structure.

A fully continuous geometric center symmetric cross-shaped graphene structure is proposed. Each cross-shaped graphene unit cell is composed of a central graphene region and four completely symmetric graphene chips, where each graphene chip acts as both bright and dark modes simultaneously, while the central graphene region always acts as the bright mode. Through destructive interference, the structure can realize the single plasmon-induced transparency (PIT) phenomenon, where the optical responses are independent of the polarization direction of the linearly polarized light due to the symmetry of the structure. Combining numerical simulations with coupled mode theory (CMT) calculations, the modulation of the Fermi energy of graphene to the optical spectra is investigated. The results show that the spectra are blue shifted as the Fermi energy increases, and the absorption of the two absorption peaks is basically equal (48.7%) when the Fermi energy increases to 0.667 eV. Theoretical calculations show that the slow light performance of the designed structure enhances with the increase of Fermi energy, where the maximum group index is high up to 424.73. Furthermore, it is worth noting that the electrode can be made very small due to its fully continuous structure. This work provides guidance in terms of terahertz modulators, tunable absorbers, and slow light devices.

Liquid-Flowing Graphene Chip-Based High-Resolution Electron Microscopy.

The recent advances in liquid-phase transmission electron microscopy represent tremendous potential in many different fields and exciting new opportunities. However, achieving both high-resolution imaging and operando capabilities remain a significant challenge. This work suggests a novel in situ imaging platform of liquid-flowing graphene chip TEM (LFGC-TEM) equipped with graphene viewing windows and a liquid exchange system. The LFGCs are robust under high-pressure gradients and rapid liquid circulation in ranges covering the experimental conditions accessible with conventional thick SiNx chips. LFGC-TEM provides atomic resolution for colloidal nanoparticles and molecular-level information limits for unstained wet biomolecules and cells that are comparable to the resolutions achievable with solid-phase and cryogenic TEM, respectively. This imaging platform can provide an opportunity for live imaging of biological phenomena that is not yet achieved using any current methods.

Viability of Neural Cells on 3D Printed Graphene Bioelectronics.

Parkinson’s disease (PD) is the second most common neurodegenerative disease in the United States after Alzheimer’s disease (AD). To help understand the electrophysiology of these diseases, N27 neuronal cells have been used as an in vitro model. In this study, a flexible graphene-based biosensor design is presented. Biocompatible graphene was manufactured using a liquid-phase exfoliation method and bovine serum albumin (BSA) for further exfoliation. Raman spectroscopy results indicated that the graphene produced was indeed few-layer graphene (FLG) with 0.11. Inkjet printing of this few-layer graphene ink onto Kapton polyimide (PI) followed by characterization via scanning electron microscopy (SEM) showed an average width of ≈868 µm with a normal thickness of ≈5.20 µm. Neuronal cells were placed on a thermally annealed 3D printed graphene chip. A live–dead cell assay was performed to prove the biosensor biocompatibility. A cell viability of approximately 80% was observed over 96 h, which indicates that annealed graphene on Kapton PI substrate could be used as a neuronal cell biosensor. This research will help us move forward with the study of N27 cell electrophysiology and electrical signaling.

Synchrotron infrared nanospectroscopy on a graphene chip.

A recurring goal in biology and biomedicine research is to access the biochemistry of biological processes in liquids that represent the environmental conditions of living organisms. These demands are becoming even more specific as microscopy techniques are fast evolving in the era of single cell analysis. In the modality of chemical probes, synchrotron infrared spectroscopy (μ-FTIR) is a technique that is extremely sensitive to vibrational responses of materials; however, the classical optical limits prevent the technique to access the biochemistry of specimens at the subcellular level. In addition, due to the intricate environmental requirements and strong infrared absorption of water, μ-FTIR of bioprocesses in liquids remains highly challenging. In phase with these challenges, on-chip liquid cells emerge as a versatile alternative to control the water thickness while providing a biocompatible chemical environment for analytical analyses. In this work we report the development of a liquid platform specially designed for nanoscale infrared analysis of biomaterials in wet environments. A key advantage of our designed platform is the use of graphene as an optical window that interfaces wet and dry environments in the liquid cell. By combining near-field optical microscopy and synchrotron infrared radiation, we measure the nanoscale fingerprint IR absorbance of a variety of liquids often used in biological studies. Further, we demonstrate the feasibility of the platform for the chemical analysis of protein clusters immersed in water with a clear view of the proteins' secondary structure signatures. The simplicity of the proposed platform combined with the high quality of our data makes our findings a template for future microfluidic devices targeting dynamic nanoscale-resolved chemical analysis.

(Invited) Suspended Graphene-Based Sensor for Real-Time and Highly Sensitive Monitoring of VOCs

Volatile organic compounds (VOCs) are emitted from solids or liquids with high vapor pressure and are often combustible and toxic, so on site real-time monitoring is vital. Currently photoionization detectors (PIDs) are used for VOC monitoring. PID devices are bulky and expensive to make and operated at high voltage to operate. As such there is a need for more portable and less expensive methods for detecting VOCs. We developed a novel gas sensor for (VOCs) detection. This technology utilizes suspended graphene membranes to provide real-time, ultrasensitive VOC detection. A freestanding graphene film suspended over an array of cavities or trench can offers increased surface area (twice over) and gives a direct method of sensing when VOCs adsorbed at the surface of graphene. Our sensor requires low voltages to operate, immediate response, high sensitivity and a larger theoretical range of detection than photoionization detectors sensors and it is a non-specific as PIDs. In this work, we shall present a 3 mm X 3 mm square chip, fabricated using conventional photolithography, containing an array of two terminal devices. Each individual device consists of a monolayer graphene sheet suspended over multiple cavities and clamped by two metal contacts. Suspended graphene, as opposed to substrate-based graphene, significantly reduces the surface charge hindrances and allows for ultrasensitive detection of gas molecules. The fabricated graphene chip has been successfully tested for toluene vapors. Currently, testing is underway to functionalize graphene for selective detection of different gases.

Suspended Graphene-Based Electrochemical Sensor for Ultra-Sensitive Detection of Electroactive Dopamine (neurotransmitter) Signals

Graphene – a single atom thick 2D material, has demonstrated extraordinary potential as ultrasensitive and specific biological and chemical sensors1,2. This is because every carbon atom in suspended graphene is a surface atom which can be covalently/non-covalently interfaced with a wide range of chemical/biological species3 for detection at the single molecule level. Additionally, the charge transport through graphene can be modified via liquid gating, which forms a sensitive electrochemical method of detecting signals from charged species bonded to the graphene surface. Recently, graphene has demonstrated selective detection of electroactive signals from dopamine-a catecholamine neurotransmitters, which are found in the mammalian central nervous system4. Pristine graphene’s superior electronic and electrochemical properties can be exploited as analytical electrochemical sensors for measuring exocytosis during communication between cells under in vitro conditions, thereby monitoring cognitive and behavioural functions of living organisms We have developed a 3 mm X 3 mm graphene chip with an array of two terminal devices, connected in parallel, in which each individual device consists of a monolayer graphene suspended over multiple cavities and clamped by two metal contacts. Suspended graphene, as opposed to substrate-based graphene, significantly reduces the surface charge hindrances and allows for ultrasensitive detection of electroactive signals. The fabricated graphene chip has been successfully tested as a VOC and electrochemical sensor. Currently, testing is underway to use the device as an electrochemical dopamine sensor. We intend to discuss initial electrochemical dopamine sensing results as well as to explore possible collaborations with research groups for testing the graphene chip as an in-vitro neurotransmitter sensor.

Relativistic Brownian motion on a graphene chip

Relativistic Brownian motion can be inexpensively demonstrated on a graphene chip. The interplay of stochastic and relativistic dynamics, governing the transport of charge carrier in graphene, induces noise-controlled effects such as (i) a stochastic effective mass, detectable as a suppression of the particle mobility with increasing the temperature; (ii) transverse harmonic mixing, whereby electron transport can be controlled by two orthogonal, commensurate ac drives; (iii) a transverse ratchet effect, measurable as a net current orthogonal to an ac drive on an asymmetric substrate, and (iv) chaotic stochastic resonance. Such properties can be of practical applications in the emerging graphene technology.

Interaction of Ethylene Carbonate and Graphene Chip: Density Functional Theory Study

Density functional theory (DFT) calculations have been applied to complexes composed of ethylene carbonate (EC) with a graphene chip to theoretically elucidate the interaction of EC with the graphene. A graphene chip consisting of 14 benzene rings and one EC molecule were examined as the interaction system. Ten binding sites of EC were examined as binding e points around the graphene chip. EC binds to a hexagonal position corresponding to the central of benzene ring of graphene surface. In addition, EC can bind to the edge region of graphene. The energy of EC in the edge region was 4.2 kcal/mol more stable than that of the hexagonal position. The activation barriers for diffusion of EC on the graphene surface were significantly low (less than 0.2 kcal/mol), indicating that EC, put on the surface, can move freely on the graphene surface and then down into the edge region.

Interaction of Ethylene Carbonate and Graphene Chip: Density Functional Theory Study

Interaction of Ethylene Carbonate and Graphene Chip: Density Functional Theory Study

Density Functional Theory Study of the Interaction of Magnesium Ions with Graphene Chip

The interaction of magnesium atom (Mg) and ionic species (Mg+ and Mg2+) with graphene chip (finite sized graphene) have been investigated by means of density functional theory (DFT) method. The B3LYP/6-31G(d) calculation showed that the Mg atom does not make a chemical bind to the graphene chip. On the other hand, the ionic species can bind srongly to a hexagonal site of graphene chip. Time-dependent (TD)-DFT calculation of Mg+ doped graphene showed that the first excitation band is assigned to a charge transfer band from a π-orbital of graphene chip (HOMO: highest occupied molecular orbital) to a singly occupied molecular orbital (SOMO) composed of Mg+(3s) orbital, whereas the second excitation band is composed of a π–π* transition corresponding to the HOMO–lowest unoccupied molecular orbital (LUMO) excitation of free graphene chip. The nature of the interaction between the Mg ions and the graphene chip was discussed on the basis of theoretical results.

Density Functional Theory Study of the Interaction of Magnesium Ions with Graphene Chip

The interaction of magnesium atom (Mg) and ionic species (Mg+ and Mg2+) with graphene chip (finite sized graphene) have been investigated by means of density functional theory (DFT) method. The B3LYP/6-31G(d) calculation showed that the Mg atom does not make a chemical bind to the graphene chip. On the other hand, the ionic species can bind srongly to a hexagonal site of graphene chip. Time-dependent (TD)-DFT calculation of Mg+ doped graphene showed that the first excitation band is assigned to a charge transfer band from a π-orbital of graphene chip (HOMO: highest occupied molecular orbital) to a singly occupied molecular orbital (SOMO) composed of Mg+(3s) orbital, whereas the second excitation band is composed of a π–π* transition corresponding to the HOMO–lowest unoccupied molecular orbital (LUMO) excitation of free graphene chip. The nature of the interaction between the Mg ions and the graphene chip was discussed on the basis of theoretical results.

Density Functional Theory Study on the Water Clusters on Graphene Chip

The structures and electronic states of graphene–water interaction systems have been investigated by means of density functional theory (DFT) method to elucidate the effects of water clusters on the electronic states of graphene chip. Solvation caused by five to eight water molecules (n = 5–8) was examined as the interaction systems. A graphene chip composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water clusters interact with the graphene chip with hydrogen bonds. The band gap of graphene was slightly red-shifted by the solvation and the first excitation energy was saturated around n = 5. The electronic states of graphene–water systems were discussed on the basis of theoretical results.

Density Functional Theory Study of Boron- and Nitrogen-Atom-Doped Graphene Chips

The structures and electronic states of boron- and nitrogen-substituted graphene chips (B-, N-, and BN-doped graphene chips) have been investigated by means of the density functional theory (DFT) method in order to shed light on the mechanism of change in the electronic properties of graphene chips caused by heteroatoms. The atomic charge of nitrogen atoms in N-graphene was a negative value, whereas that of boron atoms in B-graphene was positive. In the case of the BN-doped graphene chip, a charge polarization such as Bδ+–Nδ- was found. It was also found that the B–N bond pair is preferentially formed because of the large heat of formation of the B–N bond. The BN-doped graphene chips showed a large red shift of the band gap compared with that of normal graphene. The electric states of BN-graphenes were discussed on the basis of theoretical results.

Density Functional Theory Study on the Water Clusters on Graphene Chip

The structures and electronic states of graphene–water interaction systems have been investigated by means of density functional theory (DFT) method to elucidate the effects of water clusters on the electronic states of graphene chip. Solvation caused by five to eight water molecules (n = 5–8) was examined as the interaction systems. A graphene chip composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water clusters interact with the graphene chip with hydrogen bonds. The band gap of graphene was slightly red-shifted by the solvation and the first excitation energy was saturated around n = 5. The electronic states of graphene–water systems were discussed on the basis of theoretical results.