Graphene Field-effect Transistors Research Articles

Elucidating the time-dependent charge neutrality point modulation of polymer-coated graphene field-effect transistors in an ambient environment.

The charge neutrality point (CNP) is one of the essential parameters in the development of graphene field-effect transistors (GFETs). For GFET with an intrinsic graphene channel layer, the CNP is typically near-zero-volt gate voltage, implying that a well-balanced density of electrons and holes exists in the graphene channel layer. Fabricated GFET, however, typically exhibits CNP that is either positively or negatively shifted from the near-zero-volt gate voltage, implying that the graphene channel layer is unintentionally doped, leading to a unipolar GFET transfer characteristic. Furthermore, the CNP is also modulated in time, indicating that charges are dynamically induced in the graphene channel layer. In this work, understanding and mitigating the CNP shift were attempted by introducing passivation layers made of polyvinyl alcohol and polydimethylsiloxane onto the graphene channel layer. The CNP was found to be negatively shifted, recovered back to near-zero-volt gate voltage, and then positively shifted in time. By analyzing the charge density, carrier mobility, and correlation between the CNP and the charge density, it can be concluded that positive CNP shifts can be attributed to the charge trapping at the graphene/SiO2interface. The negative CNP shift, on the other hand, is caused by dipole coupling between dipoles in the polymer layer and carriers on the surface of the graphene layer. By gaining a deeper understanding of the intricate mechanisms governing the CNP shifts, an ambiently stable GFET suitable for next-generation electronics could be realized.

Process Development of a Liquid-Gated Graphene Field-Effect Transistor Gas Sensor for Applications in Smart Agriculture

A compact, multi-channel ionic liquid-gated graphene field-effect transistor (FET) has been proposed and developed in our work for on-field continuous monitoring of nitrate nitrogen and other nitrogen fertilizers to achieve sustainable and efficient farming practices in agriculture. However, fabricating graphene FETs with easy filling of ionic liquids, minimal graphene defects, and high process yields remains challenging, given the sensitivity of these devices to processing conditions and environmental factors. In this work, two approaches for the fabrication of our graphene FETs were presented, evaluated, and compared for high yields and easy filling of ionic liquids. The process difficulties, major obstacles, and improvements are discussed herein in detail. Both devices, those fabricated using a 3 μm-thick CYTOP® layer for position restriction and volume control of the ionic liquid and those using a ~20 nm-thick photosensitive hydrophobic layer for the same purpose, exhibited typical FET characteristics and were applicable to various application environments. The research findings and experiences presented in this paper will provide important references to related societies for the design, fabrication, and application of liquid-gated graphene FETs.

Development of a graphene field effect transistor-based immersible biosensor for immunodetection of the birch pollen allergen Bet v 1 in air samples

Pollen traps, the current gold standard to determine pollen load and thereby the allergy season, are not sufficient to determine the allergenic risk. Therefore, the establishment of highly sensitive assays for allergen measurement is of highest interest. Herein, a graphene field-effect transistor (GFET) was constructed on an interdigitated electrodes chip to develop an immersible biosensor, which was used to detect the major birch pollen allergen Bet v 1. Graphene was wet-transferred on interdigitated electrodes that contain a reference electrode used as a liquid gate in the GFET. Using a standard ELISA protocol, two different anti-Bet v 1 antibodies were chosen and immobilized on graphene for the specific capture of the target allergen. The sensitivity of the GFET biosensor was evaluated using a standard Ag/AgCl liquid gate electrode and a reference electrode when the chip was immersed in Bet v 1-containing solutions. The results showed a higher performance and sensitivity for Bet v 1 detection compared to a mediator release method, one of the most sensitive assays for allergen detection. Compared with conventional methods of allergen detection, these immersible biosensors significantly improved the speed and level of detection providing the foundation of a point-of-need platform for in-field application. Furthermore, the proposed technique provides both a new biosensor for allergen detection and a strategy for designing low-cost integrated biosensors.

Duplex-specific-nuclease-assisted graphene field-effect transistor biosensor: a novel platform for preamplification-free detection of cancer related miRNA

The pivotal role of microRNA (miRNA) in cancer diagnosis and monitoring is well recognized, yet current detection methods remain complex and costly, given the rarity of tumor miRNA in the bloodstream. This study proposes a simple and elegant miRNA sensing platform utilizing duplex-specific nuclease (DSN) and ultrasensitive graphene field-effect transistor (GFET) biosensors. The DSN-assisted GFET enables preamplification-free detection of miR-21, a promising cancer biomarker, at dilutions down to 25 aM. Along with the successful validation of its excellent specificity using clinical plasma samples without RNA extraction process, this innovative approach holds great promise for improving cancer diagnostics and monitoring.

Fabrication of graphene field effect transistors on complex non-planar surfaces

Graphene field effect transistors (GFETs) are promising devices for biochemical sensing. Integrating GFETs onto complex non-planar surfaces could uncap their potential in emerging areas of wearable electronics, such as smart contact lenses and microneedle sensing. However, the fabrication of GFETs on non-planar surfaces is challenging using conventional lithography approaches. Here, we develop a combined spray-coating and photolithography setup for the scalable fabrication of GFETs on non-planar surfaces and demonstrate their application as integrated GFETs on microneedles. We optimize the setup to pattern ∼ 67 μm long GFET channels across the microneedle tips. Graphene is deposited between photo-patterned electrodes by spray-coating a liquid-phase exfoliated graphene ink while monitoring the channel resistance to achieve the required conductivity. The formation of the GFET channels is confirmed by SEM and EDX mapping, and the GFETs are shown to modulate in solution. This demonstrates an approach for manufacturing graphene electronic devices on complex non-planar surfaces like microneedles and opens possibilities for wearable GFET microneedle sensors for real-time monitoring of biomarkers.

Bridging basic science and applied diagnostics: Comprehensive viral diagnostics enabled by graphene-based electronic biosensor technology advancements

This study presents a graphene field-effect transistor (gFET) biosensor with dual detection capabilities for SARS-CoV-2: one RNA detection assay to confirm viral positivity and the other for nucleocapsid (N-)protein detection as a proxy for infectiousness of the patient. This technology can be rapidly adapted to emerging infectious diseases, making an essential tool to contain future pandemics. To detect viral RNA, the highly conserved E-gene of the virus was targeted, allowing for the determination of SARS-CoV-2 presence or absence using nasopharyngeal swab samples. For N-protein detection, specific antibodies were used. Tested on 213 clinical nasopharyngeal samples, the gFET biosensor showed good correlation with RT-PCR cycle threshold values, proving its high sensitivity in detecting SARS-CoV-2 RNA. Specificity was confirmed using 21 pre-pandemic samples positive for other respiratory viruses. The gFET biosensor had a limit of detection (LOD) for N-protein of 0.9 pM, establishing a foundation for the development of a sensitive tool for monitoring active viral infection. Results of gFET based N-protein detection corresponded to the results of virus culture in all 16 available clinical samples and thus it also proved its capability to serve as a proxy for infectivity. Overall, these findings support the potential of the gFET biosensor as a point-of-care device for rapid diagnosis of SARS-CoV-2 infection and indirect assessment of infectiousness in patients, providing additional information for clinical and public health decision-making.

Fabrication of Graphene-based Ammonia Sensors: A Review

Abstract: Graphene gas sensors have gained much scientific interest due to their high sensitivity, selectivity, and fast detection of various gases. This article summarizes the research progress of graphene gas sensors for detecting ammonia gas at room temperature. Firstly, the performance and development trends of the graphene/semiconductor Schottky diode sensor are discussed. Secondly, manufacturing methods and the latest developments in graphene field-effect transistor sensors are reviewed. Finally, the basic challenges and latest efforts of functional ammonia gas sensors are studied. The discussion delves into each sensor type's detection principles and performance indicators, including selectivity, stability, measurement range, response time, recovery time, and relative humidity. A comparative analysis is conducted to highlight the progress achieved in research, elucidating the advantages, disadvantages, and potential solutions associated with various sensors. As a result, the paper concludes by exploring the future development prospects of graphene-based ammonia sensors.

Rapid miRNA detection enhanced by exponential hybridization chain reaction in graphene field-effect transistors

Scalable electronic devices that can detect target biomarkers from clinical samples hold great promise for point-of-care nucleic acid testing, but still cannot achieve the detection of target molecules at an attomolar range within a short timeframe (<1 h). To tackle this daunting challenge, we integrate graphene field-effect transistors (GFETs) with exponential target recycling and hybridization chain reaction (TRHCR) to detect oligonucleotides (using miRNA as a model disease biomarker), achieving a detection limit of 100 aM and reducing the sensing time by 30-fold, from 15 h to 30 min. In contrast to traditional linear TRHCR, our exponential TRHCR enables the target miRNA to initiate an autocatalytic system with exponential kinetics, significantly accelerating the reaction speed. The resulting reaction products, long-necked double-stranded polymers with a negative charge, are effectively detected by the GFET through chemical gating, leading to a shift in the Dirac voltage. Therefore, by monitoring the magnitude of this voltage shift, the target miRNA is quantified with high sensitivity. Consequently, our approach successfully detects 22-mer miRNA at concentrations as low as 100 aM in human serum samples, achieving the desired short timeframe of 30 min, which is congruent with point-of-care testing, and demonstrates superior specificity against single-base mismatched interfering oligonucleotides.

Drug evaluation platform based on non-destructive and real-time in situ organoid fate state monitoring by graphene field-effect transistor

3D organoid models have been widely used in drug evaluation because they effectively mimic physiological conditions and cell–cell interactions. However, current organoid-based drug evaluation heavily relies on invasive methods like qRT-PCR and immunofluorescence quantification, which disrupts the organoid’s structure and physiological function during the evaluation process. Therefore, it is urgent to develop a non-destructive drug evaluation platform to continuously monitor organoid fate. Here, a non-destructive and real-time in situ platform based on field effect transistor sensor (NDRS-FET) was developed to monitor organoid fate and obtained accurate drug evaluation by conducting the dynamic models. Using liver organoid as the model, the transition kinetics of liver organoid fate in response to candidate drug compounds were recorded by the NDRS-FET platform. OSM, FH1 and BG45 were successfully identified as effective regulators of liver organoid fate. Compared to traditional methods, the NDRS-FET platform could not only accurately capture the drug effect on organoid in real time, but also reduce the intergroup deviation among samples, providing more accurate and reliable tool for drug development and screening.

Transfer-free p-type graphene field-effect transistors with high mobility and on/off ratio

Graphene is considered a promising material because of the novel functionalities associated with its outstanding charge transport properties. However, because graphene has no bandgap, its electrical conductivity cannot be controlled as in semiconductors, at present. Although many attempts have been made to achieve a bandgap opening in graphene, a meaningful bandgap opening for p-type field-effect-transistors (FETs) still remains a challenge. In this study, boron-doping in transfer-free monolayer graphene was successfully demonstrated for digital logic devices. Our approach is highly versatile, as it allows the fabrication of p-type single-crystal graphene FETs having a mobility of ∼290 cm2V−1s−1, an on/off ratio of 1.9 × 105, and a subthreshold swing of 70 mVdec−1. The scalability and versatility of this transfer-free approach for the fabrication of p-type graphene FETs pave the way for high-performance p-type graphene-based digital logic circuits.

Graphene Field‐Effect Transistors for Sensing Ion‐Channel Coupled Receptors: Toward Biohybrid Nanoelectronics for Chemical Detection

AbstractGraphene field effect transistors (G‐FETs) have appeared as suitable candidates for sensing charges and have thus attracted large interest for ion and chemical detections. In particular, their high sensitivity, chemical robustness, transparency, and bendability offer a unique combination for interfacing living and soft matters. Here demonstrated their ability to sense targeted biomolecules is demonstrated, by combining them with ion channel‐coupled receptors (ICCRs). These receptors are naturally or artificially expressed within living cell membranes to generate ion fluxes in the presence of chemicals of interest. Here, those biosensors are successfully combined with a G‐FET array which converts the bio‐activation of the ICCRs into readable electronic signals. This hybrid bioelectronic device leverages the advantages of the biological receptor and the graphene field effect transistor enabling the selective detection of biomolecules, which is a current shortcoming of electronic sensors. Additionally, the G‐FET allows for discrimination of the polarity of the ion fluxes which otherwise remains hidden from conventional electrophysiological recordings. The multisite recording ability offered by the G‐FET array raises numerous possibilities for multiscale sensing and high throughput screening of cellular solutions or analytes, which is of both fundamental and applied interest in health and environment monitoring.

Gate-Switchable Molecular Diffusion on a Graphene Field-Effect Transistor.

Controlling the surface diffusion of particles on 2D devices creates opportunities for advancing microscopic processes such as nanoassembly, thin-film growth, and catalysis. Here, we demonstrate the ability to control the diffusion of F4TCNQ molecules at the surface of clean graphene field-effect transistors (FETs) via electrostatic gating. Tuning the back-gate voltage (VG) of a graphene FET switches molecular adsorbates between negative and neutral charge states, leading to dramatic changes in their diffusion properties. Scanning tunneling microscopy measurements reveal that the diffusivity of neutral molecules decreases rapidly with a decreasing VG and involves rotational diffusion processes. The molecular diffusivity of negatively charged molecules, on the other hand, remains nearly constant over a wide range of applied VG values and is dominated by purely translational processes. First-principles density functional theory calculations confirm that the energy landscapes experienced by neutral vs charged molecules lead to diffusion behavior consistent with experiment. Gate-tunability of the diffusion barrier for F4TCNQ molecules on graphene enables graphene FETs to act as diffusion switches.

Digitalization of Enzyme-Linked Immunosorbent Assay with Graphene Field-Effect Transistors (G-ELISA) for Portable Ferritin Determination.

Herein, we present a novel approach to quantify ferritin based on the integration of an Enzyme-Linked Immunosorbent Assay (ELISA) protocol on a Graphene Field-Effect Transistor (gFET) for bioelectronic immunosensing. The G-ELISA strategy takes advantage of the gFET inherent capability of detecting pH changes for the amplification of ferritin detection using urease as a reporter enzyme, which catalyzes the hydrolysis of urea generating a local pH increment. A portable field-effect transistor reader and electrolyte-gated gFET arrangement are employed, enabling their operation in aqueous conditions at low potentials, which is crucial for effective biological sample detection. The graphene surface is functionalized with monoclonal anti-ferritin antibodies, along with an antifouling agent, to enhance the assay specificity and sensitivity. Markedly, G-ELISA exhibits outstanding sensing performance, reaching a lower limit of detection (LOD) and higher sensitivity in ferritin quantification than unamplified gFETs. Additionally, they offer rapid detection, capable of measuring ferritin concentrations in approximately 50 min. Because of the capacity of transistor miniaturization, our innovative G-ELISA approach holds promise for the portable bioelectronic detection of multiple biomarkers using a small amount of the sample, which would be a great advancement in point-of-care testing.

Impact of Water-Water Correlation at Suspended Graphene/Water Interface Under Different Electro-Modulated

Graphene-based devices have extensive applications in aqueous environments. The molecular interactions across the graphene sheet significantly impact various devices, although few researches focused on elucidating the interface effects. In this study, we utilize trench structure to make graphene unilaterally and bilaterally suspended in water. The conduction status of both lateral and longitudinal currents (Id, Is, Ig) of graphene was monitored under two suspension scenarios to investigate the changes in interface evolution with the introduction of solvent-solvent interactions. For unilaterally suspended graphene, the current perpendicular to the graphene channel direction remains in the off state. For bilaterally suspended graphene, the current path is formed vertically between the graphene channel and the gate electrode, perpendicular to the direction of the graphene. This experimental setup illustrates the possibilities for exploring interfacial characteristics at the interface between 2D materials and solutions through practical experimentation.The detailed fabrication process of the graphene field-effect-transistor (GFET) device is depicted in Fig. 1. To fabricate the microchannel structure, a microfluidic pattern was generated through photolithography on the SiO2/Si substrate spun with a layer of photoresist. Then, the corresponding microchannel pattern with a thickness of 300 nm SiO2 and 30 μm Si layer was etched by reactive-ion etching (RIE) to form a trench capable of storing water. Afterward, Au electrodes were placed next to the microfluidic channel via evaporation utilizing a shadow mask. The second critical step involves the preparation of graphene. Graphene sheets were grown on a copper foil through the chemical vapor deposition (CVD) method. With the support of PMMA film, physically stacked graphene bilayer graphene was transferred to the target substrate. Ultimately, the suspended bilayer graphene was submerged in acetone for 24 hours to remove the PMMA layer and immersed in isopropanol (IPA) and DI water to clean the residues.According to this device structure, we successfully fabricate the suspension of graphene unilaterally or bilaterally in water. When introducing water through the trench, the bottom surface of the suspended graphene contacts with water molecules, while the upper surface of the suspended graphene is exposed to air. This configuration leads to a unilateral suspension in water (unilateral-suspension GFET). Conversely, when water is introduced through the trench and water is also added above the graphene channel, graphene comes into contact with water on both sides. This configuration results in its bilateral suspension in the water (bilateral-suspension GFET). The electronic transport characteristics of unilateral-suspension GFET and bilateral-suspension GFET were measured by Agilent semiconductor analysis B1500A. The gate voltage was applied to water through an Ag/AgCl electrode. Fig. 2 (a) displays the Raman spectroscopy of suspended graphene on GFET device. The most notable features of the Raman spectrum are the G peak around 1580 cm-1, and the 2D band around 2700 cm-1, which are typical characteristics of graphene. The ID/IG ratio of 0.19 indicates the good quality of the graphene layers. As shown in Fig. 2 (b), the scanning electron microscope (SEM) result of suspended graphene on the GFET device verifies the presence of large-area graphene. The diagram displays a clear demarcation line, facilitating the identification of graphene presence on the substrate. This can also imply the excellent quality of graphene with few defects.The transport behavior of unilateral-suspension GFET and bilateral-suspension GFET are measured individually, as shown in Fig. 3. The sum (ΔI) of The drain current behavior (Id) and source current behavior (Is), and gate current behavior (Ig) are recorded with changed gate voltages (from -1V to +1V) and constant VDS (VDS= 0.1V). For unilateral-suspension GFET, ΔI and Ig keep constant at zero, and there is no conduction path perpendicular to the graphene channel direction. For bilateral-suspension GFET, ΔI and Ig at positive gate voltage are opposite in direction and equal in absolute value, this indicates the formation of an obvious path between the channel and gate electrode. The apparent interfacial evolution is believed to change with the introduction of the other side of water.In conclusion, we compare the electrical characteristics shown by two different suspension situations of graphene-based field effect transistors. There are some interesting results of the conduction path relating to interfacial evolution. This result has potential for chemical sensing or battery application. Furthermore, it can contribute to fundamental research about the interface interaction between suspended graphene and water. Figure 1

(Nanocarbons Division SES Young Investigator Award) Surface Chemistry of Nanocarbon Field-Effect Transistors: From Fundamental Physics to Biosensing

Conductive carbon nanomaterials are particularly well-suited to form field-effect biosensors (bioFETs) because they are stable in aqueous media and can be chemically coupled to biomolecules. Their reduced dimensionality, either 2D (graphene) or 1D (carbon nanotubes), is key to their sensitivity: because they are entirely surfaces, these materials present remarkable electrical transport properties that are easily altered by microscopic surface interactions. Biochemical processes occurring in close proximity to their surface can therefore be transduced as changes in their electrical conductance. Selectivity for specific biochemical events, however, must be engineered via functionalization of the nanomaterial, i.e. by modifying its surface with bioactive or biorecognition elements (e.g., antibodies, aptamers, enzymes, polymer layer). Our group recently analyzed a corpus of studies presenting graphene field-effect transistors (GFETs) as bioanalytical sensors for the quantitative detection of biomarkers in the form of nucleic acids, proteins, ions or small molecules [1]. We found a striking variance in the reported sensing performance between these studies, that could not be explained by controlling for differences in graphene material, analyte type and for evolution over the years. Our hypothesis is that the lack of microscopic control on the biointerface is likely the most important source of variation in such bioFETs, highlighting the critical need to improve our knowledge and control of the functionalization of nanocarbon materials.In this talk, I will discuss our work investigating the interplay between surface chemistry and electrical properties in nanocarbon field-effect transistors. In the first part, I will focus on covalent additions using aryldiazonium salts. I will review what we have learned on the fundamental physics of this chemistry from experiments and simulations on carbon nanotube devices [2-5], in particular on its disruptive character because of the formation of sp 3 defects in the carbon lattice. More recently, we investigated this same chemistry on GFET devices and observed a heterogeneous response in their electrical conductance. Aiming to solve this, we developed a novel approach to precisely trigger and stop the reaction in situ using the applied gate voltage [6], enabling unprecedented control on the functionalization rate and yield on GFETs. In the second part, I will describe our ongoing efforts to characterize and control the biofunctionalization of GFETs through non-covalent pyrene derivatives, using a combination of electrical measurements, microscopy and spectroscopy techniques, and theoretical simulations. Finally, I will discuss our ongoing translational projects in oncology, on adapting nanocarbon-based bioFETs in cancer diagnostics applications.[1] Béraud et al, Analyst 146 (2), 403-428 (2021)[2] Bouilly et al, Applied Physics Letters 101 (5), 053116 (2012)[3] Bouilly et al, ACS nano 9 (3), 2626-2634 (2015)[4] Bouilly et al, Nano Letters 16 (7), 4679-4685 (2016)[5] Côté et al, Physical Chemistry Chemical Physics 24 (7), 4174-4186 (2021)[6] Bazan et al, Nano Letters 22 (7), 2635-2642 (2022)

Programmable Graphene e-Nose Sensor Arrays for Fast, Sensitive, and Label-Free Identification of Chemical Vapors

Conventional nanoelectronic chemical vapor sensors are mostly based on charge transfer mechanisms. The presence of vapor molecules interacts with the sensing material, resulting in changes in charge density in the channel; the resulting conductance change can subsequently be detected as changes in the current signals. This charge transfer-based mechanism naturally requires strong molecule-sensor interaction in order to achieve high sensitivity. However, the strong binding of analytes to the sensor surface will inevitably lead to slow response time and slow sensor recovery, making it unsuitable for applications requiring rapid monitoring of chemical vapors.To address this challenge, our groups previously demonstrated a new type of fast, sensitive, and broad-spectrum electronic vapor sensor by exploiting the fringing field capacitance effect in the graphene field-effect transistor (GFET). The typically trivial fringing field capacitance change due to analyte absorption is greatly amplified by both the graphene transistor and a micro-flow channel covering the surface of graphene. Different from the charge-transfer process in traditional sensors, when molecules of analytes flow through the surface of the graphene transistor, its local dielectric environment is altered which results in changes in the fringing capacitance. This molecular fringing gate effect can be amplified intrinsically by the large transconductance of the GFET. Instead of using AC spectroscopy, this capacitance change can be measured conveniently as a peak in DC current.1 In this work, a programmable graphene e-nose sensor array with electrical gates design and enhanced packaging will be demonstrated to achieve true label-free sensing and identification of chemical vapors. Individual graphene sensors within the 1D sensor array (up to 1 x 9) can be optimized to offer sensitive (down to picogram) and fast (sub-second) detection toward a variety of analytes. Figure 1 demonstrates the prototype of the graphene sensor array. Each sensor chip consists of two parts: an array of nine GFETs with a dimension of 15mm by 15mm (Figure 1(A)), and a 40cm long micro-column chip with a column width of 20-60 μm fabricated on a silicon wafer with 200nm of SiO2 by using DRIE (Deep Reactive Ion Etching) (Figure 1(B)). These two components were then bonded by epoxy and the assembled sensor chip is shown in Figure 1(C). The graphene transistor array was fabricated by transferring CVD graphene onto a silicon substrate with 200nm of thermally grown SiO2. Individual gold metal back gates were fabricated underneath the graphene film with 200nm Al2O3 deposited by ALD (atomic layer deposition) as the gate dielectric. Devices with single or multi-layer (up to 4 layers) graphene films were fabricated and tested.The fabricated graphene sensors have near-perfect device yield and a resistance range within 2 ~ 10 kΩ. Figure 1(D) and 1(E) shows the DC current signal changes of a typical sensor within the array when vapor-phase analytes of different masses were injected through a benchtop gas chromatography (GC) setup. 9 ng and 6 ng of Hexanal injection generated current peaks with peak heights of 0.8 μA and 0.5 μA, and peak width (full width at half maximum) of 1.8 seconds and 2 seconds, respectively. The high signal-to-noise ratio (~ 80 to 1) and the short response time demonstrate the high sensitivity and fast detection capability of the graphene sensor. Figure 1(E) shows a detailed sensitivity test from the injections of hexanal vapor of five different masses. The graphene sensor exhibits good linearity with a sensitivity of 79nA per nanogram of Hexanal and a 3σ detection limit of 380 picograms.We further tested the electrical gate tunability of the graphene sensor’s response. In order to eliminate the effect of graphene conductance modulation by the gate voltage, we normalize the peak height with the baseline current. As shown in Figure 1(F), when the gate voltage is programmed from -10V to +10V, the hexanal peak height is strengthened by approximately 30 percent. Similar gate voltage tuning is also observed on other analytes, such as acetone and hexanol.Our results clearly show the gate voltage tunability of the graphene sensor, suggesting a novel graphene sensor array using electrical programming rather than chemical functionalization to achieve selectivity. Combined with advanced data analysis tools, the graphene e-nose array has the potential to offer label-free chemical vapor sensing without the need to individually functionalize each sensor as in traditional e-nose devices. Furthermore, we will discuss the integration of the graphene e-nose sensor array with a micro-gas chromatography chip and a smartphone-sized custom PCB board for programming, readout, and Bluetooth data communication. W. Zang et al., Nano Lett., 21, 10301–10308 (2021). Figure 1

(Invited) Developing a Graphene Field-Effect Biosensor for Genetic Biomarkers: Simulations Unveil How the Device Sensitivity Is Related to DNA-Graphene Interactions at the Nanoscale

Graphene field-effect transistor biosensors (GFETs) offer a promising platform to detect cancer DNA biomarkers at low concentration [1]. At their core, they have an electronic circuit containing a graphene sheet – a two-dimensional nanomaterial made of a single layer of carbon atoms – whose electronic properties are very sensitive to nearby electric charges. Leveraging that feature, the electrical current generated by a GFET can thus be made very sensitive to the concentration of a specific DNA sequence in a biological sample. To achieve this, the complementary DNA sequence is linked to the graphene to bind specifically the target DNA. In most GFETs, the link is done using 1-pyrenebutanoic acid succinimidyl ester (PBASE) because its pyrene group stacks on the graphene through pi-pi interactions, without disrupting the electronic properties of the graphene. However, recent experiments in the Bouilly group have shown variations in GFET sensitivity depending on the incubation time of graphene with PBASE.Here, we use a computational approach developed in our previous work [2] to investigate at the nanoscale the role of PBASE linker molecules on the sensitivity of the GFET. First, we use molecular dynamics simulations to characterize the conformational ensemble of a 10-nt single-stranded DNA sequence linked to a graphene sheet using PBASE. Second, we estimate the electrical response of the GFET from the electrostatic potential generated by these DNA conformations on the graphene, as determined using electrostatic Poisson-Boltzmann simulations. Our results show that the conformational ensemble of DNA is strongly affected by the presence of other PBASE adsorbed on the graphene, thus changing the electrostatic potential generated on the graphene. The predicted change of the electrostatic potential should impact measurably the detection signal of the GFET.We are now using these simulations to explain the experimental characterizations of a GFET designed to detect a genetic biomarker important in breast cancer profiling. Our simulations have the potential to support the development of GFETs with better sensitivity for DNA detection.[1] Béraud, A., Sauvage, M., Bazán, C. M., Tie, M., Bencherif, A., and Bouilly, D. (2021) Graphene field-effect transistors as bioanalytical sensors: design, operation and performance. Analyst. 146:403-428.[2] Côté, S., Mousseau, N., and Bouilly, D. (2022) The molecular origin of the electrostatic gating of single-molecule field-effect biosensors investigated by molecular dynamics simulations. Phys. Chem. Chem. Phys. 24:4174-4186.

Enhanced electrical performance in graphene field-effect transistors through post-annealing of high-k HfLaO gate dielectrics

High-k gate dielectrics have attracted a great deal of attention in the investigation of transistors due to their unique properties such as superior gate controllability. However, their integration into graphene field-effect transistors (GFETs) remains problematic and the physical mechanisms governing the performance of these devices are still not fully understood. In this study, the effects of post-annealing on GFETs utilizing the high-k HfLaO ternary oxide as the gate dielectric were comprehensively investigated. The HfLaO film was deposited on top of graphene by magnetron sputtering, and the device performance with various post-annealing temperatures was conducted. It was found that post-annealing temperature can effectively increase the dielectric constant through balancing the oxygen-vacancy defects and moisture absorption. Both the surface morphology of HfLaO and performance of GFETs were investigated, and the fabricated GFETs exhibit notable electrical performance enhancements. Specifically, GFETs with a 200 °C post-annealed HfLaO gate dielectric demonstrate the optimal device performance, featuring a minimal Dirac point voltage (VDirac) of 1.1 V and a minimal hysteresis (ΔVDirac) of 0.5 V. The extracted hole and electron mobilities are 4012 and 1366 cm2/V · s, respectively, nearly one order of magnitude higher than that of GFETs with as-deposited HfLaO. This work outperforms other existing GFETs utilizing high-k gate dielectric and chemical vapor deposition grown graphene in terms of both carrier mobility and on–off ratio. It is also noted that the excessive post-annealing temperature can negatively impact the GFET performance through introducing oxygen vacancies, increasing the surface roughness, lowering the breakdown voltage, and inducing recrystallization.

Nano Thermal Simulation of Graphene Field Effect Transistor Based on Ballistic Diffusive Model

This paper investigates temperature evolution in graphene field-effect transistors. We present a refined Ballistic-diffusive equation model (BDE) tailored for scrutinizing the phonon transport within GNRFET transistors. Furthermore, we examine the influence of the channel length on thermal characteristics. COMSOL Multiphysics is employed to compute the phonon transport and temperature distribution in nano-GNRFET. Our results reveal that the phonon transport anticipated by the suggested BDE model closely corresponds to that derived from the Boltzmann transport equation. The proposed model proficiently gauges the thermal performance of GNRFET, with the outcomes suggesting that the characteristic length of the GNR has a negligible impact on the temperature increase.

Modular Fabrication of Microfluidic Graphene FET for Nucleic Acids Biosensing.

Graphene field-effect transistors (GFETs) are widely used in biosensing due to their excellent properties in biomolecular signal amplification, exhibiting great potential for high-sensitivity and point-of-care testing in clinical diagnosis. However, difficulties in complicated fabrication steps are the main limitations for the further studies and applications of GFETs. In this study, a modular fabrication technique is introduced to construct microfluidic GFET biosensors within 3 independent steps. The low-melting metal electrodes and intricate flow channels are incorporated to maintain the structural integrity of graphene and facilitate subsequent sensing operations. The as-fabricated GFET biosensor demonstrates excellent long-term stability, and performs effectively in various ion environments. It also exhibits high sensitivity and selectivity for detecting single-stranded nucleic acids at a 10fm concentration. Furthermore, when combined with the CRISPR/Cas12a system, it facilitates amplification-free and rapid detection of nucleic acids at a concentration of 1fm. Thus, it is believed that this modular-fabricated microfluidic GFET may shed light on further development of FET-based biosensors in various applications.