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Biological and Medical Applications of Materials and Interfaces

Enantioselective Detection of Gaseous Odorants with Peptide–Graphene Sensors Operating in Humid Environments
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  • Yui Yamazaki
    Yui Yamazaki
    Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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  • Tatsuru Hitomi
    Tatsuru Hitomi
    Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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  • Chishu Homma
    Chishu Homma
    Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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  • Tharatorn Rungreungthanapol
    Tharatorn Rungreungthanapol
    Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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  • Masayoshi Tanaka
    Masayoshi Tanaka
    Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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    Orcidhttps://orcid.org/0000-0002-4701-5352
  • Kou Yamada
    Kou Yamada
    Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
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  • Hiroshi Hamasaki
    Hiroshi Hamasaki
    Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
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  • Yoshiaki Sugizaki
    Yoshiaki Sugizaki
    Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
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  • Atsunobu Isobayashi
    Atsunobu Isobayashi
    Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
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  • Hideyuki Tomizawa
    Hideyuki Tomizawa
    Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
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  • Mina Okochi
    Mina Okochi
    Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
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    Orcidhttps://orcid.org/0000-0002-1727-2948
  • Yuhei Hayamizu*
    Yuhei Hayamizu
    Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0003-1411-9400
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ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2024, 16, 15, 18564–18573
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https://doi.org/10.1021/acsami.4c01177
Published April 3, 2024

Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under

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Abstract

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Replicating the sense of smell presents an ongoing challenge in the development of biomimetic devices. Olfactory receptors exhibit remarkable discriminatory abilities, including the enantioselective detection of individual odorant molecules. Graphene has emerged as a promising material for biomimetic electronic devices due to its unique electrical properties and exceptional sensitivity. However, the efficient detection of nonpolar odor molecules using transistor-based graphene sensors in a gas phase in environmental conditions remains challenging due to high sensitivity to water vapor. This limitation has impeded the practical development of gas-phase graphene odor sensors capable of selective detection, particularly in humid environments. In this study, we address this challenge by introducing peptide-functionalized graphene sensors that effectively mitigate undesired responses to changes in humidity. Additionally, we demonstrate the significant role of humidity in facilitating the selective detection of odorant molecules by the peptides. These peptides, designed to mimic a fruit fly olfactory receptor, spontaneously assemble into a monomolecular layer on graphene, enabling precise and specific odorant detection. The developed sensors exhibit notable enantioselectivity, achieving a remarkable 35-fold signal contrast between d- and l-limonene. Furthermore, these sensors display distinct responses to various other biogenic volatile organic compounds, demonstrating their versatility as robust tools for odor detection. By acting as both a bioprobe and an electrical signal amplifier, the peptide layer represents a novel and effective strategy to achieve selective odorant detection under normal atmospheric conditions using graphene sensors. This study offers valuable insights into the development of practical odor-sensing technologies with potential applications in diverse fields.

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Introduction

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Biogenic volatile organic compounds (BVOCs) are a kind of volatile organic compound synthesized predominantly in plants. BVOCs have become more important in several fields, such as health care, environmental monitoring, food, and the agricultural industry. (1,2) For example, the emission of BVOCs to air from plants is closely related to the environments and climates (3,4) and is also associated with plant diseases. (5−7) Thus, the detection of BVOCs in air is crucial for the above field to monitor the environmental conditions of plants. Furthermore, the detection of BVOCs at customs in airports and harbors is becoming more important for plant protection and quarantine. It is desirable to develop automated systems to detect plants and related materials on behalf of quarantine dogs. (8,9)
The sensing of the BVOCs has been conducted by gas chromatography–mass spectrometry (GC-MS), quartz crystal microbalance (QCM), and surface plasmon resonance (SPR) in the past. Although the GC-MS is the most reliable and common technique, (10,11) the equipment is relatively large, and small and mobile devices are preferable for ubiquitous usage at farm fields or border customs. QCM (12) and LSPR (13) sensors can be relatively small in their dimensions. The surface functionalization of these sensors is the key to achieving the selective detection of BVOCs. The molecular imprinting technique and ionic liquid immobilization exhibited significant progress in the selective detection of BVOCs, and there are several demonstrations of monitoring BVOCs in the air. (14−16) However, considering applications in quality control of plants in farms and quarantine at airports, it is still challenging to develop a sensing system that satisfies (1) small size, (2) stability against ambient conditions containing water vapor, (3) low power consumption, and (4) high sensitivity and selectivity.
Graphene has attracted much attention as an active material for sensing due to its high mobility, large specific area, and accessibility for surface modification. The successful detection of 1 ppm NO2 and water molecules was achieved using graphene field effect transistors (GFETs). (17) To date, GFETs have demonstrated the detection of multiple volatile organic compounds, such as NH3, (18) CO2, (18,19) and NO2. (20,21) More recently, GFET-base sensors identify “odor molecules” combined with machine learning to selectively obtain molecule-specific responses. (22,23) Selective sensing has also been improved by modifying the graphene surface with polymers (24) and ssDNA. (25)
Despite this progress, GFET-based BVOC sensors require further improvement in more practical environments where stable operation under various humidity levels is required. So far, graphene has been reported to respond to water vapors at high sensitivity (1 ppm level). (17) The electrical and chemical properties of pristine graphene depend on the humidity in the environment. (26,27) Furthermore, transistor-based graphene sensors have difficulty detecting nonpolar molecules, i.e., most odorant molecules. Therefore, it is crucial to establish a novel interface between graphene and atmospheric air to achieve a stable operation while simultaneously maintaining high selectivity and sensitivity simultaneously.
In this study, we present a novel method for detecting BVOCs under humid conditions using peptides designed to functionalize the surface of graphene sensors. Our peptides consist of an assembly domain and bioprobe for the detection of BVOCs. Specifically, our peptide design includes probe domains that mimic the olfactory receptor of fruit flies, which have high selectivity for limonene. The probe domain connects with an assembly domain that can form ordered structures on graphene surfaces in a self-assembly manner, allowing for the formation of a uniform peptide layer in a simple way. Unlike untreated graphene sensors, our peptide-functionalized graphene sensors showed a stable response to the BVOCs even under humid conditions. We achieved 35-fold contrast in the electrical signal for enantioselective detection of limonene. Interestingly, the sensors selectively detected enantiomers only in the presence of water vapor. We also tested three different peptide probes and obtained distinct electrical responses for multiple kinds of BVOCs. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) confirmed this trend. Our results demonstrate the potential of peptide-engineered graphene sensors as a versatile tool for selective BVOC detection under humid conditions.

Results and Discussion

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Functionalization of Graphene Surfaces by Peptides

Developing the bioprobe is the key to producing more practical odor sensors. The range of the probes spans from synthetic molecules and polymers (28) to engineered proteins such as olfactory receptors. (9) The flat surface and high surface area of graphene are suitable for surface functionalization and characterization. Owing to these advantages, the high sensitivity and selectivity of graphene odor biosensors have been achieved by integrating the bioprobes immobilized on the graphene surface. (29−31) Olfactory receptors as a bioprobe have demonstrated outstanding sensitivity and selectivity against amyl butyrate. (32,33) However, the fragility of these proteins hinders the long-term stability of the graphene odor sensors. Peptides are an alternative candidate that mimics the olfactory receptors’ properties and have demonstrated odor sensing using multiple platforms. (34)
Our recent work has demonstrated the selective detection of odor molecules using GFETs functionalized with insect olfactory receptor mimicking peptides, where the graphene odor sensors were operated under liquid conditions. (35) In this work, we propose a strategy to operate GFETs for BVOC sensing in the gas phase. The challenge here is the stable operation of graphene odor sensors functionalized with peptides with high selectivity in a gas phase in the presence of water vapor. Graphene is generally sensitive to adsorbed polar molecules, including water molecules. (17,18,36) It has been a significant obstacle to the use of graphene odor sensors in ordinary environments containing water vapor.
Similar to prior studies, (35,37−39) we employed peptides with self-assembly capability into molecular films on surfaces, accomplished through a series of surface processes involving adsorption, diffusion, and intermolecular interactions. Noncovalent interactions between the peptides and the surface facilitate their surface diffusion, eventually leading to their ordering along specific directions (Figure 1a). Peptides used in this work are named GR3R, P1, and LBP3 (Figure 1b). Our peptides are composed of two functional domains: (1) an assembly domain and (2) a probe domain. The assembly domain includes dipeptide repeats of glycine (G) and alanine (A), with two arginines (R) at both ends of the sequence. All peptides have GGG as a spacer for the bioprobes, in addition to the GA repeats. P1 and LBP3 share the assembly domain with the sequence of GR3R. (35,37) P1 and LBP3 contain the probe domain as a bioprobe for the target odor molecules in addition to the assembly domain. Our recent findings (35) highlighted that a mixed solution of P1 peptides and GR3R at several mixing ratios formed a coassembled peptide layer on a graphite surface with monomolecular thickness. Furthermore, the ordered molecular films were found to maintain their self-assembled structures stably even under liquid conditions. These bifunctional peptides are designed to create a uniform monomolecular thick layer on graphene, while the probe domain actively captures BVOCs on the surface. The resultant binding events can be electrically detected by a change in graphene conductivity.

Figure 1

Figure 1. Surface functionalization of graphene biosensor for the detection of biogenic volatile organic compounds. (a) Schematic showing the peptide self-assembly on graphene and the peptide-graphene odor sensors operating in the presence of water vapor. (b) Peptide sequences. Peptides consist of three domains: probe, linker, and assembly domain. (c) Molecular structures of the biogenic volatile organic molecules used in this work.

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The sequences of the probe domain are designed as follows. P1 peptide containing FLLF (F: Phenylalanine and L: Leucine) connected to the N-terminus of GR3R was rationally designed. This sequence mimics a part of the sequence of the olfactory receptor Or19a. (40−42) The sequence of the LBP3 peptide was experimentally found as a strong binder of d-limonene. (38) Short peptide libraries derived from OR19a were synthesized on a peptide array, and the amount of bound d-limonene on each peptide was analyzed, allowing a simultaneous exploration of the whole receptor protein. (38) In the demonstration, we employed d-limonene, l-limonene, (-)-menthol, methyl salicylate, and ethyl propionate as target odor molecules to evaluate the selectivity of the proposed GFET gas sensor (Figure 1c).
First, we examined whether these peptides could form a thin film on the graphite surface through self-assembly. Atomic force microscopy (AFM) showed that GR3R peptide formed a uniform thin film on the surface with a thickness of about 1.5 nm (Figure S1), consistent with a previous work. (37) P1 and LBP3 also exhibited the formation of thin films on the graphite surfaces.

Effect of the Peptide Modification against Humidity

We evaluated the response of our peptide-modified odor sensor against the humidity. Three sensor chips were placed in series (Figure 2a). Three mass flow controllers regulate the flow rates of N2 carrier gases introduced to water cylinders and target odor molecules to produce each vapor independently. The mixture of gases was introduced into graphene odor sensors with controlled humidity and flow rates. An in-line humidity sensor monitored the relative humidity at the end of the gas line system (Figure S2). Each chip contains seven graphene channels with an open window of 10 μm× 30 μm between the source and drain electrodes (Figure 2b). The rest of the area was covered by a polyimide protection layer. The GFET chip was placed on a specified mount and encased within a well made of polytetrafluoroethylene (PTFE). This well was uniquely designed with two openings, serving as an inlet and an outlet for gases, thereby establishing a pathway for the gas flow to the graphene channel (Figure 2a).

Figure 2

Figure 2. Graphene sensors responding to relative humidity. (a) Schematic of the gas measurement system for the graphene odor sensor with controlled humidity and flow rate of odor molecules. (b) Optical microscopic image of a graphene sensor chip. (c) Real-time response of graphene sensors to humidity change: untreated (black) and GFET functionalized with GR3R peptides (orange). The curves and light-colored regions represent the mean and standard deviation of the data points, respectively. (d) Conductivity change of graphene depending on the relative humidity derived from panel (c). The bars indicate the standard deviations. (e) Accelerated test of untreated (black) and GFETs functionalized with GR3R peptides (orange) responding to the repeated humidity change. The curves and light-colored regions represent the mean and standard deviation, respectively.

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Our graphene sensors had a field-effect transistor structure showing a reproducible gate response before and after the peptide functionalization (Figure S3). We studied the conductivity change of the GFET against humidity. Before introducing water vapor, the GFETs were purged with pure N2 gas for 80 min to initialize the surface state. The relative humidity (RH) was then increased incrementally from 19% to 54% RH every 10 min (Figure 2c). After introducing the first vapor gas at 19% RH, the conductivity of the untreated GFET increased by 1.6%. Conductivity increased monotonically with increasing up to 44% RH.
Further increases in humidity caused the GFET response to water vapor to become unstable, decreasing by −15% at 54% RH. The negative conductivity change remained even after the graphene surface was rinsed with N2 gas. In contrast, the GFET functionalized with GR3R showed a stable response to water vapor. After introducing carrier gas at 19% RH, the conductivity increased by 2% and remained constant even when the RH was increased to 54% (Figure 2d). Comfortable humidity levels for humans in public buildings are known to be between 40% and 60% RH. For the use of graphene odor sensors in such environments, a key issue with untreated GFETs is that their humidity response becomes unstable at around 50% RH. Peptide-functionalized GFETs, on the other hand, have proven their stability.
Accelerated tests of GFETs were also conducted against repeated changes in humidity at a constant level. Figure 2e shows the conductivity change under the repeated change of the humidity with 39% and 50% RH 10 times. Both untreated and peptide-functionalized GFETs exhibited a step-function-like response against the humidity change. Notably, the untreated GFET decreased the baseline of the conductivity by 3% after a 30-time repeat. On the other hand, peptide-functionalized GFET had a stable baseline. These results indicate that peptides act as stabilizers on the graphene surface against humidity change.
The conductivity change in graphene when exposed to water vapor has been extensively studied. (26,27,43−46) The mechanism behind this change in conductivity due to adsorbed water molecules is multifaceted, potentially involving hole doping, (45) band gap tuning, (43) interaction with the SiO2 surface of the substrate, (44) and intercalation of water molecules between the graphene and the substrate. (46) The observed increase in conductivity (Figure 2c) is likely attributable to hole doping of graphene by water molecules. The significant decrease in conductivity at high humidity levels observed in untreated graphene sensors may result from a combination of these mechanisms. In contrast, sensors using peptide-functionalized graphene showed a remarkable insensitivity to changes in humidity. This is possibly because the peptides act as a buffer for water molecules, wherein the water molecules are absorbed into the peptide monolayer, maintaining stable electrical polarization within the dielectric medium of the peptides, even under varying humidity levels. This hypothesis is further corroborated by environmental AFM measurements of the self-assembled peptides. These measurements, conducted in a controlled humidity chamber, reveal an increase in peptide thickness under varying humidity conditions, as illustrated in Figure S4.

Enantioselective Detection of Limonene

Limonene is a molecule with two enantiomers that humans can selectively recognize. d-Limonene is perceived as a lemon scent, while l-limonene is perceived as a turpentine scent. Our peptide-functionalized GFETs were tested for detecting both d- and l-limonene (Figure 3). Prior to measurement, the GFET was exposed to a N2 carrier gas or 53% RH gas until the conductivity of the GFET became stable. Once a steady state was reached, limonene gas was injected three times at different concentrations of target molecules. The target gas injection lasted 10 min as the “ON” state, followed by 10 min of purging with 53% RH carrier gas as the “OFF” state. The odorant molecule gas flow rate was increased by 1, 5, and 10 sccm during each ON cycle. In this way, we evaluated the binding and desorption of limonene molecules.

Figure 3

Figure 3. Chiral recognition by GFETs functionalized with peptides. Conductivity changes of GFETs responding to enantiomers of limonene under (a, b) 53% RH and (c, d) N2 conditions. The curves show the responses of GFETs to d-limonene (red) and l-limonene (blue). The chiral selectivity differed between untreated GFETs and those functionalized by LBP3 peptides. The curves and colored shadows represent the mean value and standard deviation, respectively.

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The changes in the conductivity clearly illustrate the difference between the untreated and peptide-functionalized GFETs. In the untreated GFETs, the conductivity increased upon introduction of the enantiomers during the ON state. Subsequently, the conductivity gradually decreased upon switching to the OFF state. The average magnitudes of the conductivity changes were similar for d- and l-limonene (Figure 3a). On the other hand, peptide-functionalized GFETs responded only to d-limonene, with almost no signals for l-limonene. The difference in the conductivity changes between d- and l-limonene was 35-fold, demonstrating the significant enantioselectivity of LBP3 for d-limonene (Figure 3b).
The response of GFETs to d- or l-limonene vapors is intricately linked to the presence of water molecules. When tests were conducted under dry conditions, using only N2 gas, untreated GFET revealed the same responses to d- and l-limonene vapors (Figure 3c). Furthermore, LPB3 functionalized GFET had a notable decrease in selectivity was observed (Figure 3d and Figure S5). This outcome suggests that the molecular interactions between the peptides and odorant molecules are significantly influenced by the water molecule content at the graphene interface. The presence of water molecules likely imparts flexibility to the peptides, enabling them to capture odorant molecules in an energetically favorable manner, thereby enhancing the selectivity. This interface is optimally suited for use in normal air conditions, where humidity is present.
Previously, the enantioselective detection of odorant molecules using graphene sensors has been demonstrated with limited selectivity of less than 2-fold. (47) The significant contrast observed in this work was achieved with the peptide probe. The fundamental role of the peptide layer in our GFETs is to differentiate between very similar molecules such as d-limonene and l-limonene in this case. The peptide-functionalized GFETs work on a mechanism in which the peptides specifically interact with the odorant molecules, causing a change in the electrical properties of the sensor. This interaction is highly dependent on the structural fit between the peptide and the odorant molecule. In our case, LBP3 peptides have a preferential binding toward d-limonene due to its specific structure (Figure S6), resulting in a more significant response for d-limonene than for l-limonene. This leads to a much higher selectivity; despite a reduced overall signal intensity, this effect is more pronounced under the conditions with humidity.

Selective Detection for Other Odorant Molecules

We selected other odorant molecules to test the selectivity of the sensors. (-)-Menthol, methyl salicylate, and ethyl propionate are produced by plants in nature. Although these molecules have similar molecular weights, they smell distinctly like peppermint, root beer, and pineapple, respectively. In the electrical measurements, the ON and OFF states of the target molecules were examined at three different flow rates in the same manner as in Figure 3. Untreated GFETs exhibited relatively large responses in the conductivity for all odorant molecules, and there was no significant difference in their magnitudes among them (Figure 4a).

Figure 4

Figure 4. Real-time measurement of peptide-functionalized GFETs for each odorant molecule. Real-time response of GFETs to each odorant gas with incrementally increasing flow rates. Each plot shows the results of (a) untreated GFETs, and GFETs functionalized with (b) GR3R, (c) P1, and (d) LBP3. The colors of the curves represent the individual odorant gas: d-limonene (red), (-)-menthol (green), methyl salicylate (purple), and ethyl propionate (black). (e) Bar plot of the conductivity magnitudes at 10 min after 10 sccm of odorant gas injection. Real-time response of (f) untreated GFETs and (g) GFETs functionalized with GR3R peptides under N2 conditions. All curves represent the mean value of the conductivity change among the multiple channels.

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In contrast, peptide-functionalized GFETs showed a variety of responses for different odorant molecules (Figure 4b–d). Interestingly, (-)-menthol and methyl salicylate resulted in a decrease in conductivity, while d-limonene exhibited an increase in conductivity. Ethyl propionate had a more complex trend in the response, where GR3R increased conductivity but P1 and LBP3 decreased. In the case of GR3R, in particular, the change in conductivity during the ON state was negative, while the overall conductivity increased on average. Figure 4e summarizes the magnitudes of the responses in the GFETs against each target molecule, and Table S1 (Supporting Information) lists the vapor concentration at a flow rate of 10 sccm. First, LBP3 shows a significant selectivity. d-Limonene leads to a positive and large change in the conductivity, and other molecules have negative changes. In addition, GR3R and P1 have a small response to D-limonene.
The sign of the conductivity change, positive or negative, should have a strong correlation with the target molecule. As shown in a previous report investigating graphene sensors for the detection of various analytes, (22) aromatic molecules tended to increase the conductivity of the graphene by their direct adsorption on the surfaces. This increase in the conductivity is consistent with our observations in the untreated GFETs, which show an increase in conductivity after introducing odorant molecules under pure N2 (Figure 4f) and 50% RH (Figure 4a) conditions.
The magnitudes of the responses in untreated GFETs were larger under humid conditions (Figure 4a) compared with dry conditions (Figure 4f), suggesting that the dipoles of water molecules at the graphene interface could enhance the signal along with the adsorption of odorant molecules. On the other hand, in the case of peptide-functionalized GFETs, the water effect is more crucial. The sign of the conductivity change was negative or positive depending on the odorant molecules. This phenomenon can be related to the peptide film on the surface, which can act as a receptor for the target molecules and a reservoir for water molecules. The absorbed odorant molecules can sensitively change the dielectric constant of the mixture of peptides and water molecules. The peptide film containing water molecules can be considered as a dynamic medium that responds to target molecules. Indeed, the responses of the untreated and peptide-functionalized GFETs were similar under dry conditions (Figure 4f,g). Notably, under humid conditions, the estimated limits of detection (LOD) of the untreated and LBP3 GFETs for d-limonene were 3.0 and 7.5 ppm, respectively. These LODs were smaller when measured under humid conditions than under dry conditions (Figure S7 and Table S2).
In this Discussion, we explore potential explanations for the distinctive features of peptide-functionalized GFETs. The interactions between graphene sensors and odorant molecules, along with the observed differences between untreated and peptide-functionalized GFETs, are primarily understood through the physicochemical properties of these molecules and specific sensing mechanisms. In untreated GFETs, the detection of various odorant molecules largely depends on their physical adsorption on the graphene surface. This adsorption process changes the charge distribution on graphene, consequently altering its conductivity. The magnitude of this change in conductivity is significantly affected by factors such as the hydrophobicity of the odorant molecule, its molecular size, polarizability, and affinity for the graphene surface.
In contrast, peptide-functionalized GFETs involve more specific interactions between the odorant molecules and the peptides. These peptides are chosen for their ability to selectively interact with certain odorant molecules. When an odorant molecule binds to a peptide, it triggers a conformational change in the peptide, impacting the local electronic environment of the graphene and thus changing its conductivity.
The difference in signal responses between untreated and peptide-functionalized GFETs for each specific odorant can be attributed to the enhanced selectivity provided by the peptides. These peptides not only selectively interact with specific odorant molecules but also reduce responses to other molecules. Based on these considerations, we interpret that this selectivity leads to more distinct signal responses to various odorants in peptide-functionalized GFETs compared to their untreated counterparts.

Classification of Odorant Molecules by PCA

To further analyze the selectivity of peptide-functionalized GFETs, we performed principal component analysis (PCA) and hierarchical cluster analysis (HCA) (Figures S8 and S9). PCA is an analytical method for building linear multivariate models from multidimensional data sets. (22,23,48) Figure 5 shows the results of the first two principal components. These contain > 86% of original data in their contributions (Figure S9). PCA results show a significant amount of overlap between d-limonene and other odorants in untreated GFETs, although l-limonene is relatively separated from the others (Figure 5a). Peptide-functionalized GFETs revealed considerable selectivity for some odorant molecules (Figure 5b–d). The LBP3 peptide separated d-limonene well from others along the PC1 axis. The GR3R and P1 peptides also separated ethyl propionate from (-)-menthol and methyl salicylate, indicating that these two peptides respond specifically to ethyl propionate. The PCA indicated that the LBP3 peptide was the most specific receptor to d-limonene.

Figure 5

Figure 5. Discriminative detection of BVOCs by peptide-functionalized GFETs. (a–d) Principal component analysis score plots of GFETs for different odorants. (e) Dendrogram of LBP3 peptide generated by hierarchical cluster analysis.

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In order to evaluate the selectivity more comprehensively, we also performed an HCA. HCA is a method that groups similar sample data into the same cluster in the space on the feature values. (48,49) The distance between the samples measured the similarity of each sample. The dendrogram of the HCA results for peptide-functionalized GFETs shows the formation of an independent cluster of d-limonene. In contrast, the untreated GFETs do not discriminate specific BVOC (Figure 5e and Figure S10). This result is consistent with the PCA (Figure 5 a–d).

Conclusions

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This study introduces peptide-functionalized graphene sensors as a new approach for the selective and stable detection of odor molecules in the gas phase with humidity including the enantioselective recognition of limonene. Our results demonstrate that these sensors provide a stable response under different humidity conditions. LBP3, among the peptides tested, exhibited the highest magnitude of conductivity change in response to d-limonene, indicating its specific response as an artificial odorant receptor. The achieved enantioselective detection of limonene with a 35-fold contrast in the electrical signal is significant since previous studies on enantioselective detection of odorant molecules using graphene sensors have shown limited selectivity of less than 2-fold. Furthermore, our findings suggest that the presence of water molecules is the key to achieving remarkable selectivity. The LBP3 peptide can compete with odorant receptors in terms of enantioselectivity, which is promising for the development of biomimetic systems that have great potential for the understanding function of proteins (50) and practical applications, such as plant monitoring in farms, quarantine in airports, and environmental monitoring. The diversity of peptide design also offers the opportunity to produce an array of sensors with multiple types of peptides, thus allowing for the tuning of analyte selectivity. (51) Our study highlights the potential for biomimetic peptide functionalization of graphene sensors as a new approach for odorant sensing under normal air conditions with humidity.

Experimental Section

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Peptide Preparation

GR3R and P1 peptides used in this study were purchased from the Toray Research Center, Inc. LBP3 peptide was synthesized with a purity higher than 90%. Peptide solutions were stored in a −20 °C freezer. Frozen peptide solutions were heated up to 70 °C for 15 min and allowed to reach room temperature.

Atomic Force Microscopy (AFM) Measurements and Sample Preparation

In sample preparation for AFM measurements, Si substrates were first annealed on a hot plate at 200 °C for 30 min. After annealing, graphite flakes were transferred to Si substrates using a mechanical exfoliation method. 500-nM peptide solution was incubated for 1 h at room temperature. After incubation, the solution was removed by blowing with N2 gas.
The surface morphology of the peptide was characterized by using an atomic force microscope (Agilent 5500 and Asylum Cypher) in air. The surface morphology was measured in tapping mode (AC mode). The AFM instrument was equipped with a silicon cantilever (OMCL-AC160TS-R3, Olympus, Japan) with a resonance frequency of 300 kHz and a spring constant of 26 N/m.

GFET Fabrication

Graphene was synthesized by chemical vapor deposition (CVD) and transferred to a Si wafer. Graphene and electrodes (50 nm Au and 5 nm Ti) were patterned by photolithography. Whole GFET chips were covered with polyimide as a protective shield, and only the graphene channels were exposed in the open window. The distance between the electrodes was 20 μm, and the width of the graphene was 30 μm. Each chip has seven channels, and we measured all channels simultaneously.

Peptide Functionalization of the GFET Chip

500-nM peptide solution was placed on the graphene surfaces of the GFET chip at room temperature and kept for one hour. After incubation, the solution was removed by blowing with N2 gas.

Materials

The odor molecules utilized in this work were d-limonene ((R)-(+)-limonene, Fujifilm Wako Pure Chemical Co., Ltd., Japan, purity > 95.0%), l-limonene ((S)-(-)-limonene, Fujifilm Wako Pure Chemical Co., Ltd., Japan, purity > 98.0%), methyl salicylate (Tokyo Chemical Industry Co., Ltd., Japan, purity > 99.0%), (-)-menthol (l-menthol, (1R,2S,5R)-(-)-menthol, Tokyo Chemical Industry Co., Ltd., Japan, purity > 99.0%), and ethyl propionate (Fujifilm Wako Pure Chemical Co., Ltd., Japan, purity > 97.0%).

Gas Flow Setup

The homemade gas sensing system using this work is shown in Figure S2. Detailed information about the gas sensing system is provided in the Supporting Information.

GFET Measurements

GFETs were measured by using a homemade electrical measurement device produced by TOSHIBA Corporation. While drain current was measured, we set the drain voltage (Vd) at 16 or 20 mV, and back gate voltage (Vg) at 0 V. Drain voltage was chosen with the maximum value in the Id measurable range. The real-time response of the drain current was measured every 0.5 s. For data analysis, we used Igor Pro 9 (WaveMetrics) and Python.

Calculation of gas concentration

Odorant gas concentration was calculated using a saturated vapor pressure. Detailed information is provided in the Supporting Information.

Calculation of Conductivity Change

We obtained the conductivity change of the GFETs as follows. The average value for one min before the introduction of water vapor or odorant molecule gas was taken as the initial value σ0 and the conductivity was normalized by dividing by this value.

Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA)

PCA and HCA methods were performed using Python (scikit-learn (52)) and Igor 9 (WaveMetrics), respectively. A detailed protocol of PCA and input data are presented in the Supporting Information. For the HCA, the same parameters as in PCA were used (Figure S6). We employed the Euclidean method and the Ward method to calculate the distance between each sample and to form the clusters, respectively.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.4c01177.

  • Structure of the peptides on the graphite and graphene surface; homemade gas sensing system with graphene field effect transistors (GFETs); chiral recognition of limonene with peptide-functionalized GFETs; long-term observation of limonene sensing; the detection limit of limonene gas using peptide-functionalized GFETs; principal component analysis (PCA) and hierarchical cluster analysis (HCA) (PDF)

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
  • Authors
    • Yui Yamazaki - Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
    • Tatsuru Hitomi - Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
    • Chishu Homma - Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
    • Tharatorn Rungreungthanapol - Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
    • Masayoshi Tanaka - Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan;  Orcidhttps://orcid.org/0000-0002-4701-5352
    • Kou Yamada - Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
    • Hiroshi Hamasaki - Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
    • Yoshiaki Sugizaki - Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
    • Atsunobu Isobayashi - Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
    • Hideyuki Tomizawa - Corporate Research & Development Center, Toshiba Corporation, 1, Komukai-Toshiba-Cho, Saiwai-ku, Kawasaki 212-8582, Japan
    • Mina Okochi - Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan;  Orcidhttps://orcid.org/0000-0002-1727-2948
  • Author Contributions

    M.T., H.H., K.Y., Y.S., A.I., H.T., M.O., and Y.H. designed the project. Y.Y., T.H., and C.H. performed the experiments. C.H. shared the analytical tools of principal component analysis and provided insight to understand the data. T.R. provided the peptides. Y.Y. and Y.H. analyzed the data and wrote the manuscript. All authors proofread and approved the manuscript. The manuscript was written through the contributions of all authors. All authors have approved the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the Cabinet Office (CAO), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Intelligent Processing Infrastructure of Cyber and Physical Systems” (funding agency: NEDO).

References

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    A graphene chem. vapor sensor with an unmodified surface has been fabricated and thoroughly characterized upon exposure to headspace vapor of a variety of solvents and related compds. The vapor sensor exhibits excellent discrimination towards a variety of chem. compds. Principle component anal. (PCA) was performed to explore the extent of grouping for each compd. and sepn. between compds. and chem. classes. The prediction accuracy of the sensor is evaluated with linear discrimination anal., k-nearest neighbor, random forest, and support vector classifiers. The combination of PCA and prediction accuracies demonstrate the discrimination capability of an unmodified graphene chem. vapor sensor. Such a vapor sensor is very attractive for application in small, low-power, robust, and adaptable cross-reactive arrays in electronic noses.
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  23. 23
    Capman, N. S. S.; Zhen, X. V.; Nelson, J. T.; Chaganti, V. R. S. K.; Finc, R. C.; Lyden, M. J.; Williams, T. L.; Freking, M.; Sherwood, G. J.; Bühlmann, P.; Hogan, C. J.; Koester, S. J. Machine Learning-Based Rapid Detection of Volatile Organic Compounds in a Graphene Electronic Nose. ACS Nano 2022, 16 (11), 19567– 19583,  DOI: 10.1021/acsnano.2c10240
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    Jung, H.; Park, J. Real-Time Detection of Methyl Salicylate Vapor Using Reduced Graphene Oxide and Poly (Diallyldimethylammonium Chloride) Complex. Chem. Phys. Lett. 2022, 793, 139446  DOI: 10.1016/j.cplett.2022.139446
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    24
    Real-time detection of methyl salicylate vapor using reduced graphene oxide and poly (diallyldimethylammonium chloride) complex
    Jung, Hanyung; Park, Jinhyuk
    Chemical Physics Letters (2022), 793 (), 139446CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    We report the detection of Me salicylate (MeSA) vapor with reduced graphene oxide (rGO) and a poly (diallyldimethylammonium chloride) (PDADMAC) complex. The complex was based on a graphene oxide aq. soln. where PDADMAC was dispersed and dried via photo-thermal redn. through laser irradn. to form the rGO-PDADMAC complex as a sensing matrix with a higher affinity to the target analyte, MeSA vapor. The sensor based on the rGO-PDADMAC complex was used to measure the change in resistance in real time. The rGO-PDADMAC sensor detected 11% resistance variation induced by 14.5-ppmv MeSA vapor over 540 s, while the pristine rGO sensor indicated only 1.2% resistance variation.
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  25. 25
    Lu, Y.; Goldsmith, B. R.; Kybert, N. J.; Johnson, A. T. C. DNA-Decorated Graphene Chemical Sensors. Appl. Phys. Lett. 2010, 97 (8), 083107  DOI: 10.1063/1.3483128
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    DNA-decorated graphene chemical sensors
    Lu, Ye; Goldsmith, B. R.; Kybert, N. J.; Johnson, A. T. C.
    Applied Physics Letters (2010), 97 (8), 083107/1-083107/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    Graphene is a two-dimensional material with exceptional electronic properties and enormous potential for applications. Graphene's promise as a chem. sensor material was noted but there was little work on practical chem. sensing using graphene, and in particular, how chem. functionalization may be used to sensitize graphene to chem. vapors. Here the authors show one route towards improving the ability of graphene to work as a chem. sensor by using single stranded DNA as a sensitizing agent. The resulting devices show fast response times, complete and rapid recovery to baseline at room temp., and discrimination between several similar vapor analytes. (c) 2010 American Institute of Physics.
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  26. 26
    Quellmalz, A.; Smith, A. D.; Elgammal, K.; Fan, X.; Delin, A.; Östling, M.; Lemme, M.; Gylfason, K. B.; Niklaus, F. Influence of Humidity on Contact Resistance in Graphene Devices. ACS Appl. Mater. Interfaces 2018, 10 (48), 41738– 41746,  DOI: 10.1021/acsami.8b10033
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    Hayasaka, T.; Lin, A.; Copa, V. C.; Lopez, L. P., Jr; Loberternos, R. A.; Ballesteros, L. I. M.; Kubota, Y.; Liu, Y.; Salvador, A. A.; Lin, L. An Electronic Nose Using a Single Graphene FET and Machine Learning for Water, Methanol, and Ethanol. Microsyst. Nanoeng. 2020, 6, 50,  DOI: 10.1038/s41378-020-0161-3
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    27
    An electronic nose using a single graphene FET and machine learning for water, methanol, and ethanol
    Hayasaka, Takeshi; Lin, Albert; Copa, Vernalyn C.; Lopez Jr., Lorenzo P.; Loberternos, Regine A.; Ballesteros, Laureen Ida M.; Kubota, Yoshihiro; Liu, Yumeng; Salvador, Arnel A.; Lin, Liwei
    Microsystems & Nanoengineering (2020), 6 (1), 50CODEN: MNIACT; ISSN:2055-7434. (Nature Research)
    Abstr.: The poor gas selectivity problem has been a long-standing issue for miniaturized chem.-resistor gas sensors. The electronic nose (e-nose) was proposed in the 1980s to tackle the selectivity issue, but it required top-down chem. functionalization processes to deposit multiple functional materials. Here, we report a novel gas-sensing scheme using a single graphene field-effect transistor (GFET) and machine learning to realize gas selectivity under particular conditions by combining the unique properties of the GFET and e-nose concept. Instead of using multiple functional materials, the gas-sensing cond. profiles of a GFET are recorded and decoupled into four distinctive phys. properties and projected onto a feature space as 4D output vectors and classified to differentiated target gases by using machine-learning analyses. Our single-GFET approach coupled with trained pattern recognition algorithms was able to classify water, methanol, and ethanol vapors with high accuracy quant. when they were tested individually. Furthermore, the gas-sensing patterns of methanol were qual. distinguished from those of water vapor in a binary mixt. condition, suggesting that the proposed scheme is capable of differentiating a gas from the realistic scenario of an ambient environment with background humidity. As such, this work offers a new class of gas-sensing schemes using a single GFET without multiple functional materials toward miniaturized e-noses.
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  28. 28
    Cengiz, N.; Guclu, G.; Kelebek, H.; Capanoglu, E.; Selli, S. Application of Molecularly Imprinted Polymers for the Detection of Volatile and Off-Odor Compounds in Food Matrices. ACS Omega 2022, 7 (18), 15258– 15266,  DOI: 10.1021/acsomega.1c07288
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    28
    Application of Molecularly Imprinted Polymers for the Detection of Volatile and Off-Odor Compounds in Food Matrices
    Cengiz, Nurten; Guclu, Gamze; Kelebek, Hasim; Capanoglu, Esra; Selli, Serkan
    ACS Omega (2022), 7 (18), 15258-15266CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
    A review. Molecularly imprinted polymers (MIPs) are synthetic receptors having specific cavities intended for a template mol. with a retention mechanism that depends on mol. recognition of the targeted constituent. They were initially established for the detection of minor mols. including drugs, pesticides, or pollutants. One of the most remarkable areas where MIPs have potential utilization is in food anal., esp. in terms of volatile compds. which are found in very low concns. in foods but play a crucial role for consumer preference and acceptance. In recent years, these polymers have been used extensively for sensing volatile org. and off-odor compds. in terms of food quality for selective high-extn. purposes. This review first summarizes the basic principles and prodn. processes of MIPs. Second, their recent applications in the sepn., identification, and quantification of volatile and off-odor compds. in food samples are elucidated.
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  29. 29
    Cui, Y.; Kim, S. N.; Naik, R. R.; McAlpine, M. C. Biomimetic Peptide Nanosensors. Acc. Chem. Res. 2012, 45 (5), 696– 704,  DOI: 10.1021/ar2002057
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    Kotlowski, C.; Larisika, M.; Guerin, P. M.; Kleber, C.; Kröber, T.; Mastrogiacomo, R.; Nowak, C.; Pelosi, P.; Schütz, S.; Schwaighofer, A.; Knoll, W. Fine Discrimination of Volatile Compounds by Graphene-Immobilized Odorant-Binding Proteins. Sens. Actuators B Chem. 2018, 256, 564– 572,  DOI: 10.1016/j.snb.2017.10.093
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    Lee, K.; Yoo, Y. K.; Chae, M.-S.; Hwang, K. S.; Lee, J.; Kim, H.; Hur, D.; Lee, J. H. Highly Selective Reduced Graphene Oxide (RGO) Sensor Based on a Peptide Aptamer Receptor for Detecting Explosives. Sci. Rep. 2019, 9 (1), 10297,  DOI: 10.1038/s41598-019-45936-z
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    31
    Highly selective reduced graphene oxide (rGO) sensor based on a peptide aptamer receptor for detecting explosives
    Lee Kyungjae; Yoo Yong Kyoung; Lee Junwoo; Kim Hyungsuk; Hur Don; Lee Jeong Hoon; Chae Myung-Sic; Hwang Kyo Seon
    Scientific reports (2019), 9 (1), 10297 ISSN:.
    An essential requirement for bio/chemical sensors and electronic nose systems is the ability to detect the intended target at room temperature with high selectivity. We report a reduced graphene oxide (rGO)-based gas sensor functionalized with a peptide receptor to detect dinitrotoluene (DNT), which is a byproduct of trinitrotoluene (TNT). We fabricated the multi-arrayed rGO sensor using spin coating and a standard microfabrication technique. Subsequently, the rGO was subjected to photolithography and an etching process, after which we prepared the DNT-specific binding peptide (DNT-bp, sequence: His-Pro-Asn-Phe-Se r-Lys-Tyr-IleLeu-HisGln-Arg-Cys) and DNT non-specific binding peptide (DNT-nbp, sequence: Thr-Ser-Met-Leu-Leu-Met-Ser-Pro-Lys-His-Gln-Ala-Cys). These two peptides were prepared to function as highly specific and highly non-specific (for the control experiment) peptide receptors, respectively. By detecting the differential signals between the DNT-bp and DNT-nbp functionalized rGO sensor, we demonstrated the ability of 2,4-dinitrotoluene (DNT) targets to bind to DNT-specific binding peptide surfaces, showing good sensitivity and selectivity. The advantage of using the differential signal is that it eliminates unwanted electrical noise and/or environmental effects. We achieved sensitivity of 27 ± 2 × 10(-6) per part per billion (ppb) for the slope of resistance change versus DNT gas concentration of 80, 160, 240, 320, and 480 ppm, respectively. By sequentially flowing DNT vapor (320 ppb), acetone (100 ppm), toluene (1 ppm), and ethanol (100 ppm) onto the rGO sensors, the change in the signal of rGO in the presence of DNT gas is 6400 × 10(-6) per ppb whereas the signals from the other gases show no changes, representing highly selective performance. Using this platform, we were also able to regenerate the surface by simply purging with N2.
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    Park, S. J.; Kwon, O. S.; Lee, S. H.; Song, H. S.; Park, T. H.; Jang, J. Ultrasensitive Flexible Graphene Based Field-Effect Transistor (FET)-Type Bioelectronic Nose. Nano Lett. 2012, 12 (10), 5082– 5090,  DOI: 10.1021/nl301714x
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    Ultrasensitive Flexible Graphene Based Field-Effect Transistor (FET)-Type Bioelectronic Nose
    Park, Seon Joo; Kwon, Oh Seok; Lee, Sang Hun; Song, Hyun Seok; Park, Tai Hyun; Jang, Jyongsik
    Nano Letters (2012), 12 (10), 5082-5090CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Rapid and precise discrimination of various odorants is vital to fabricating enhanced sensing devices in the fields of disease diagnostics, food safety, and environmental monitoring. Here, we demonstrate an ultrasensitive and flexible field-effect transistor (FET) olfactory system, namely, a bioelectronic nose (B-nose), based on plasma-treated bilayer graphene conjugated with an olfactory receptor. The stable p- and n-type behaviors from modified bilayer graphene (MBLG) took place after controlled oxygen and ammonia plasma treatments. It was integrated with human olfactory receptors 2AG1 (hOR2AG1: OR), leading to the formation of the liq.-ion gated FET-type platform. ORs bind to the particular odorant amyl butyrate (AB), and their interactions are specific and selective. The B-noses behave as flexible and transparent sensing devices and can recognize a target odorant with single-carbon-atom resoln. The B-noses are ultrasensitive and highly selective toward AB. The min. detection limit (MDL) is as low as 0.04 fM (10-15; signal-to-noise: 4.2), and the equil. consts. of OR-oxygen plasma-treated graphene (OR-OG) and ammonia plasma-treated graphene (-NG) are ca. 3.44 × 1014 and 1.47 × 1014 M-1, resp. Addnl., the B-noses have long-term stability and excellent mech. bending durability in flexible systems.
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  33. 33
    Kwon, O. S.; Song, H. S.; Park, S. J.; Lee, S. H.; An, J. H.; Park, J. W.; Yang, H.; Yoon, H.; Bae, J.; Park, T. H.; Jang, J. An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell. Nano Lett. 2015, 15 (10), 6559– 6567,  DOI: 10.1021/acs.nanolett.5b02286
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    An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell
    Kwon, Oh Seok; Song, Hyun Seok; Park, Seon Joo; Lee, Seung Hwan; An, Ji Hyun; Park, Jin Wook; Yang, Heehong; Yoon, Hyeonseok; Bae, Joonwon; Park, Tai Hyun; Jang, Jyongsik
    Nano Letters (2015), 15 (10), 6559-6567CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Human sensory-mimicking systems, such as electronic brains, tongues, skin, and ears, have been promoted for use in improving social welfare. However, no significant achievements have been made in mimicking the human nose due to the complexity of olfactory sensory neurons. Combinational coding of human olfactory receptors (hORs) is essential for odorant discrimination in mixts., and the development of hOR-combined multiplexed systems has progressed slowly. Here, the authors report the first demonstration of an artificial multiplexed superbioelectronic nose (MSB-nose) that mimics the human olfactory sensory system, leading to high-performance odorant discriminatory ability in mixts. Specifically, portable MSB-noses were constructed using highly uniform graphene micropatterns (GMs) that were conjugated with two different hORs, which were employed as transducers in a liq.-ion gated field-effect transistor (FET). Field-induced signals from the MSB-nose were monitored and provided high sensitivity and selectivity toward target odorants (min. detectable level: 0.1 fM). More importantly, the potential of the MSB-nose as a tool to encode hOR combinations was demonstrated using principal component anal.
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    Wasilewski, T.; Neubauer, D.; Kamysz, W.; Gębicki, J. Recent Progress in the Development of Peptide-Based Gas Biosensors for Environmental Monitoring. Case Studies in Chemical and Environmental Engineering 2022, 5, 100197  DOI: 10.1016/j.cscee.2022.100197
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    Homma, C.; Tsukiiwa, M.; Noguchi, H.; Tanaka, M.; Okochi, M.; Tomizawa, H.; Sugizaki, Y.; Isobayashi, A.; Hayamizu, Y. Designable Peptides on Graphene Field-Effect Transistors for Selective Detection of Odor Molecules. Biosens. Bioelectron. 2023, 224, 115047  DOI: 10.1016/j.bios.2022.115047
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    Designable peptides on graphene field-effect transistors for selective detection of odor molecules
    Homma, Chishu; Tsukiiwa, Mirano; Noguchi, Hironaga; Tanaka, Masayoshi; Okochi, Mina; Tomizawa, Hideyuki; Sugizaki, Yoshiaki; Isobayashi, Atsunobu; Hayamizu, Yuhei
    Biosensors & Bioelectronics (2023), 224 (), 115047CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
    Gas sensing based on graphene field-effect transistors (GFETs) has gained broad interest due to their high sensitivity. Further progress in gas sensing with GFETs requires to detection of various odor mols. for applications in the environmental monitoring, healthcare, food, and cosmetic industries. To develop the ubiquitous odor-sensing system, establishing an artificial sense of smell with electronic devices by mimicking olfactory receptors will be key. Although the application of olfactory receptors to GFETs is straightforward for odor sensing, synthetic mols. with a similar function to olfactory receptors would be desirable to realize the robust performance of sensing. In this work, we designed three new peptides consisting of two domains: a bio-probe to the target mols. and a mol. scaffold. These peptides were rationally designed based on a motif sequence in olfactory receptors and self-assembled into a mol. thin film on GFETs. Limonene, Me salicylate, and menthol were employed as representative odor mols. of plant flavors to demonstrate the biosensing of odor mols. The cond. change of GFETs against the binding to odor mols. with various concns. and the dynamic response revealed a distinct signature of three different peptides against individual species of the target mols. The kinetic response of each peptide exhibited characteristic time consts. in the adsorption and desorption process, also supported by the principal component anal. Our demonstration of the graphene odor sensors with the designed peptides opens a way to establish future peptide-array sensors with multi-sequence of peptide, realizing an odor sensing system with higher selectivity.
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    Bartošík, M.; Mach, J.; Piastek, J.; Nezval, D.; Konečný, M.; Švarc, V.; Ensslin, K.; Šikola, T. Mechanism and Suppression of Physisorbed-Water-Caused Hysteresis in Graphene FET Sensors. ACS Sens 2020, 5 (9), 2940– 2949,  DOI: 10.1021/acssensors.0c01441
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    Li, P.; Sakuma, K.; Tsuchiya, S.; Sun, L.; Hayamizu, Y. Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing. ACS Appl. Mater. Interfaces 2019, 11 (23), 20670– 20677,  DOI: 10.1021/acsami.9b04079
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    Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing
    Li, Peiying; Sakuma, Kouhei; Tsuchiya, Shohei; Sun, Linhao; Hayamizu, Yuhei
    ACS Applied Materials & Interfaces (2019), 11 (23), 20670-20677CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Self-assembled peptides have revealed uniform ordering on two-dimensional (2D) materials such as mica, graphene, and MoS2 so far. These peptides are expected to be utilized as a mol. scaffold for biosensing based on 2D materials. However, the stability of the peptide structures on 2D materials under liq. has not been evaluated, and some of the previously reported peptides may have instability under water. In this work, by mimicking an amino-acid sequence of silk protein, we successfully developed peptide sequences that can maintain ordered nanostructures even after rinsing with DI water. The structural stability was also proven under electrochem. bias, which is crucial as a biomol. scaffold for practical biosensing with 2D materials. The stability probably arises from its β-sheet like structures with improved intermol. interactions and binding to the surface of 2D materials, resulting in the formation of stable domains of ordered peptide structures. Our peptides showed its ability to immobilize probe mols. for biosensing and inhibit a non-specific adsorption through its co-assembly process. Interestingly, we found that two structural phases in the self-assembled structures, where only one of the phases reveals a binding affinity to target mols.
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  38. 38
    Rungreungthanapol, T.; Homma, C.; Akagi, K.-I.; Tanaka, M.; Kikuchi, J.; Tomizawa, H.; Sugizaki, Y.; Isobayashi, A.; Hayamizu, Y.; Okochi, M. Volatile Organic Compound Detection by Graphene Field-Effect Transistors Functionalized with Fly Olfactory Receptor Mimetic Peptides. Anal. Chem. 2023, 95 (9), 4556– 4563,  DOI: 10.1021/acs.analchem.3c00052
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    Noguchi, H.; Nakamura, Y.; Tezuka, S.; Seki, T.; Yatsu, K.; Narimatsu, T.; Nakata, Y.; Hayamizu, Y. Self-Assembled GA-Repeated Peptides as a Biomolecular Scaffold for Biosensing with MoS2 Electrochemical Transistors. ACS Appl. Mater. Interfaces 2023, 15 (11), 14058– 14066,  DOI: 10.1021/acsami.2c23227
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    Vosshall, L. B.; Wong, A. M.; Axel, R. An Olfactory Sensory Map in the Fly Brain. Cell 2000, 102 (2), 147– 159,  DOI: 10.1016/S0092-8674(00)00021-0
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    Dweck, H. K. M.; Ebrahim, S. A. M.; Kromann, S.; Bown, D.; Hillbur, Y.; Sachse, S.; Hansson, B. S.; Stensmyr, M. C. Olfactory Preference for Egg Laying on Citrus Substrates in Drosophila. Curr. Biol. 2013, 23 (24), 2472– 2480,  DOI: 10.1016/j.cub.2013.10.047
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    Dweck, H. K. M.; Ebrahim, S. A. M.; Retzke, T.; Grabe, V.; Weißflog, J.; Svatoš, A.; Hansson, B. S.; Knaden, M. The Olfactory Logic behind Fruit Odor Preferences in Larval and Adult Drosophila. Cell Rep. 2018, 23 (8), 2524– 2531,  DOI: 10.1016/j.celrep.2018.04.085
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    Yavari, F.; Kritzinger, C.; Gaire, C.; Song, L.; Gulapalli, H.; Borca-Tasciuc, T.; Ajayan, P. M.; Koratkar, N. Tunable Bandgap in Graphene by the Controlled Adsorption of Water Molecules. Small 2010, 6 (22), 2535– 2538,  DOI: 10.1002/smll.201001384
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    Tunable Bandgap in Graphene by the Controlled Adsorption of Water Molecules
    Yavari, Fazel; Kritzinger, Christo; Gaire, Churamani; Song, Li; Gulapalli, Hemtej; Borca-Tasciuc, Theodorian; Ajayan, Pulickel M.; Koratkar, Nikhil
    Small (2010), 6 (22), 2535-2538CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A facile technique to open a bandgap in graphene based on water adsorption to the graphene surface is reported. An environmental chamber with precise control of the abs. humidity level is used to control the amt. of water adsorbed to the graphene surface. This technique does not require any complicated engineering or modification of the graphene surface and does not rely on chem. doping or defect generation. However, the device will have to be equipped with an enclosure to precisely control the humidity levels. The hydration of the graphene film can be tuned by controlling the abs. humidity level of the environment.
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    Levesque, P. L.; Sabri, S. S.; Aguirre, C. M.; Guillemette, J.; Siaj, M.; Desjardins, P.; Szkopek, T.; Martel, R. Probing Charge Transfer at Surfaces Using Graphene Transistors. Nano Lett. 2011, 11 (1), 132– 137,  DOI: 10.1021/nl103015w
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    Probing Charge Transfer at Surfaces Using Graphene Transistors
    Levesque, Pierre L.; Sabri, Shadi S.; Aguirre, Carla M.; Guillemette, Jonathan; Siaj, Mohamed; Desjardins, Patrick; Szkopek, Thomas; Martel, Richard
    Nano Letters (2011), 11 (1), 132-137CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Graphene field effect transistors (FETs) are extremely sensitive to gas exposure. Charge transfer doping of graphene FETs by atm. gas is ubiquitous but not yet understood. We have used graphene FETs to probe minute changes in electrochem. potential during high-purity gas exposure expts. Our study shows quant. that electrochem. involving adsorbed water, graphene, and the substrate is responsible for doping. We not only identify the water/oxygen redox couple as the underlying mechanism but also capture the kinetics of this reaction. The graphene FET is highlighted here as an extremely sensitive potentiometer for probing electrochem. reactions at interfaces, arising from the unique d. of states of graphene. This work establishes a fundamental basis on which new electrochem. nanoprobes and gas sensors can be developed with graphene.
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  45. 45
    Smith, A. D.; Elgammal, K.; Niklaus, F.; Delin, A.; Fischer, A. C.; Vaziri, S.; Forsberg, F.; Råsander, M.; Hugosson, H.; Bergqvist, L.; Schröder, S.; Kataria, S.; Östling, M.; Lemme, M. C. Resistive Graphene Humidity Sensors with Rapid and Direct Electrical Readout. Nanoscale 2015, 7 (45), 19099– 19109,  DOI: 10.1039/C5NR06038A
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    Resistive graphene humidity sensors with rapid and direct electrical readout
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  1. Kantaro Kikuchi, Yui Yamazaki, Kohsuke Kanekura, Yuhei Hayamizu. Graphene Biosensor Differentiating Sensitive Interactions between Ribonucleic Acid and Dipeptide Repeats in Liquid–Liquid Phase Separation. ACS Applied Materials & Interfaces 2025, 17 (8) , 12765-12771. https://doi.org/10.1021/acsami.4c15382
  2. Marie Sugiyama, Ayhan Yurtsever, Nina Uenodan, Yuta Nabae, Takeshi Fukuma, Yuhei Hayamizu. Hierarchical Assembly of Hemin-Peptide Catalytic Systems on Graphite Surfaces. ACS Nano 2025, Article ASAP.
  3. Peiying Li, Chen Chen, Ayhan Yurtsever, Sijin Wu, Linhao Sun. Structural Ordering of Interfacially Assembled Silk Fibroin-Like Peptides via Robust Intermolecular Hydrogen-Bonding Networks. ACS Materials Letters 2024, 6 (9) , 3993-4001. https://doi.org/10.1021/acsmaterialslett.4c01045
  4. Andreea Gostaviceanu, Simona Gavrilaş, Lucian Copolovici, Dana Maria Copolovici. Graphene-Oxide Peptide-Containing Materials for Biomedical Applications. International Journal of Molecular Sciences 2024, 25 (18) , 10174. https://doi.org/10.3390/ijms251810174
  5. Ilaria Di Filippo, Zakaria Anfar, Gabriele Magna, Piyanan Pranee, Donato Monti, Manuela Stefanelli, Reiko Oda, Corrado Di Natale, Roberto Paolesse. Chiral porphyrin-SiO 2 nano helices-based sensors for vapor enantiomers recognition. Nanoscale Advances 2024, 6 (17) , 4470-4478. https://doi.org/10.1039/D4NA00217B
  6. Damian Neubauer. Advancements in peptide-based gas biosensors. 2024https://doi.org/10.1016/bs.coac.2024.11.001
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  • Abstract

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    Figure 1

    Figure 1. Surface functionalization of graphene biosensor for the detection of biogenic volatile organic compounds. (a) Schematic showing the peptide self-assembly on graphene and the peptide-graphene odor sensors operating in the presence of water vapor. (b) Peptide sequences. Peptides consist of three domains: probe, linker, and assembly domain. (c) Molecular structures of the biogenic volatile organic molecules used in this work.

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    Figure 2

    Figure 2. Graphene sensors responding to relative humidity. (a) Schematic of the gas measurement system for the graphene odor sensor with controlled humidity and flow rate of odor molecules. (b) Optical microscopic image of a graphene sensor chip. (c) Real-time response of graphene sensors to humidity change: untreated (black) and GFET functionalized with GR3R peptides (orange). The curves and light-colored regions represent the mean and standard deviation of the data points, respectively. (d) Conductivity change of graphene depending on the relative humidity derived from panel (c). The bars indicate the standard deviations. (e) Accelerated test of untreated (black) and GFETs functionalized with GR3R peptides (orange) responding to the repeated humidity change. The curves and light-colored regions represent the mean and standard deviation, respectively.

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    Figure 3

    Figure 3. Chiral recognition by GFETs functionalized with peptides. Conductivity changes of GFETs responding to enantiomers of limonene under (a, b) 53% RH and (c, d) N2 conditions. The curves show the responses of GFETs to d-limonene (red) and l-limonene (blue). The chiral selectivity differed between untreated GFETs and those functionalized by LBP3 peptides. The curves and colored shadows represent the mean value and standard deviation, respectively.

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    Figure 4

    Figure 4. Real-time measurement of peptide-functionalized GFETs for each odorant molecule. Real-time response of GFETs to each odorant gas with incrementally increasing flow rates. Each plot shows the results of (a) untreated GFETs, and GFETs functionalized with (b) GR3R, (c) P1, and (d) LBP3. The colors of the curves represent the individual odorant gas: d-limonene (red), (-)-menthol (green), methyl salicylate (purple), and ethyl propionate (black). (e) Bar plot of the conductivity magnitudes at 10 min after 10 sccm of odorant gas injection. Real-time response of (f) untreated GFETs and (g) GFETs functionalized with GR3R peptides under N2 conditions. All curves represent the mean value of the conductivity change among the multiple channels.

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    Figure 5

    Figure 5. Discriminative detection of BVOCs by peptide-functionalized GFETs. (a–d) Principal component analysis score plots of GFETs for different odorants. (e) Dendrogram of LBP3 peptide generated by hierarchical cluster analysis.

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      Percival, C. J.; Stanley, S.; Galle, M.; Braithwaite, A.; Newton, M. I.; McHale, G.; Hayes, W.
      Analytical Chemistry (2001), 73 (17), 4225-4228CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      A piezoelec. sensor coated with an artificial biomimetic recognition element has been developed for the detn. of L-menthol in the liq. phase. A highly specific noncovalently imprinted polymer (MIP) was cast in situ on to the surface of a gold-coated quartz crystal microbalance (QCM) electrode as a thin permeable film. Selective rebinding of the target analyte was obsd. as a frequency shift quantified by piezoelec. microgravimetry with the QCM. The detectability of L-menthol was 200 ppb with a response range of 0-1.0 ppm. The response of the MIP-QCM to a range of monoterpenes was investigated with the sensor binding menthol in favor of analogous compds. The sensor was able to distinguish between the D- and L-enantiomers of menthol owing to the enantioselectivity of the imprinted sites. To our knowledge, this is the first report describing enantiomeric resoln. within an MIP utilizing a single monomer-functional moiety interaction. It is envisaged that this technique could be employed to det. the concn. of terpenes in the atm.
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    15. 15
      Toniolo, R.; Pizzariello, A.; Dossi, N.; Lorenzon, S.; Abollino, O.; Bontempelli, G. Room Temperature Ionic Liquids as Useful Overlayers for Estimating Food Quality from Their Odor Analysis by Quartz Crystal Microbalance Measurements. Anal. Chem. 2013, 85 (15), 7241– 7247,  DOI: 10.1021/ac401151m
      There is no corresponding record for this reference.
    16. 16
      Wang, Z.; Chen, W.; Gu, S.; Wang, J.; Wang, Y. Discrimination of Wood Borers Infested Platycladus Orientalis Trunks Using Quartz Crystal Microbalance Gas Sensor Array. Sens. Actuators B Chem. 2020, 309, 127767  DOI: 10.1016/j.snb.2020.127767
      There is no corresponding record for this reference.
    17. 17
      Schedin, F.; Geim, A. K.; Morozov, S. V.; Hill, E. W.; Blake, P.; Katsnelson, M. I.; Novoselov, K. S. Detection of Individual Gas Molecules Adsorbed on Graphene. Nat. Mater. 2007, 6 (9), 652– 655,  DOI: 10.1038/nmat1967
      17
      Detection of individual gas molecules adsorbed on graphene
      Schedin, F.; Geim, A. K.; Morozov, S. V.; Hill, E. W.; Blake, P.; Katsnelson, M. I.; Novoselov, K. S.
      Nature Materials (2007), 6 (9), 652-655CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Authors show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas mol. attaches to or detaches from graphene's surface. The adsorbed mols. change the local carrier concn. in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chem. detectors but also for other applications where local probes sensitive to external charge, magnetic field or mech. strain are required.
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    18. 18
      Dan, Y.; Lu, Y.; Kybert, N. J.; Luo, Z.; Johnson, A. T. C. Intrinsic Response of Graphene Vapor Sensors. Nano Lett. 2009, 9 (4), 1472– 1475,  DOI: 10.1021/nl8033637
      18
      Intrinsic Response of Graphene Vapor Sensors
      Dan, Yaping; Lu, Ye; Kybert, Nicholas J.; Luo, Zhengtang; Johnson, A. T. Charlie
      Nano Letters (2009), 9 (4), 1472-1475CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Graphene is a two-dimensional material with extremely favorable chem. sensor properties. Conventional nanolithog. typically leaves a resist residue on the graphene surface, whose impact on the sensor characteristics has not yet been detd. The contamination layer chem. dopes the graphene, enhances carrier scattering, and acts as an absorbent layer that concs. analyte mols. at the graphene surface, thereby enhancing the sensor response. The authors demonstrate a cleaning process that verifiably removes the contamination on the device structure and allows the intrinsic chem. responses of the graphene monolayer to be measured. These intrinsic responses are surprisingly small, even upon exposure to strong analytes such as NH3 vapor.
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    19. 19
      Yoon, H. J.; Jun, D. H.; Yang, J. H.; Zhou, Z.; Yang, S. S.; Cheng, M. M.-C. Carbon Dioxide Gas Sensor Using a Graphene Sheet. Sens. Actuators B Chem. 2011, 157 (1), 310– 313,  DOI: 10.1016/j.snb.2011.03.035
      19
      Carbon dioxide gas sensor using a graphene sheet
      Yoon, Hyeun Joong; Jun, Do Han; Yang, Jin Ho; Zhou, Zhixian; Yang, Sang Sik; Cheng, Mark Ming-Cheng
      Sensors and Actuators, B: Chemical (2011), 157 (1), 310-313CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      Reported is on a high-performance graphene CO2 gas sensor fabricated by mech. cleavage. Unlike other solid-state gas sensors, the graphene sensor can be operated under ambient conditions and at room temp. Changes in the device conductance are measured for various concns. of CO2 gas adsorbed on the surface of graphene. The conductance of the graphene gas sensor increases linearly when the concn. of CO2 gas is increased from 10-100 ppm. The advantages of this sensor are high sensitivity, fast response time, short recovery time, and low power consumption.
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    20. 20
      Kim, Y. H.; Kim, S. J.; Kim, Y.-J.; Shim, Y.-S.; Kim, S. Y.; Hong, B. H.; Jang, H. W. Self-Activated Transparent All-Graphene Gas Sensor with Endurance to Humidity and Mechanical Bending. ACS Nano 2015, 9 (10), 10453– 10460,  DOI: 10.1021/acsnano.5b04680
      20
      Self-Activated Transparent All-Graphene Gas Sensor with Endurance to Humidity and Mechanical Bending
      Kim, Yeon Hoo; Kim, Sang Jin; Kim, Yong-Jin; Shim, Yeong-Seok; Kim, Soo Young; Hong, Byung Hee; Jang, Ho Won
      ACS Nano (2015), 9 (10), 10453-10460CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Graphene is considered as one of leading candidates for gas sensor applications in the Internet of Things owing to its unique properties such as high sensitivity to gas adsorption, transparency, and flexibility. The authors present self-activated operation of all graphene gas sensors with high transparency and flexibility. The all-graphene gas sensors which consist of graphene for both sensor electrodes and active sensing area exhibit highly sensitive, selective, and reversible responses to NO2 without external heating. The sensors show reliable operation under high humidity conditions and bending strain. In addn. to these remarkable device performances, the significantly facile fabrication process enlarges the potential of the all-graphene gas sensors for use in the Internet of Things and wearable electronics.
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    21. 21
      Pearce, R.; Iakimov, T.; Andersson, M.; Hultman, L.; Spetz, A. L.; Yakimova, R. Epitaxially Grown Graphene Based Gas Sensors for Ultra Sensitive NO2 Detection. Sens. Actuators B Chem. 2011, 155 (2), 451– 455,  DOI: 10.1016/j.snb.2010.12.046
      21
      Epitaxially grown graphene based gas sensors for ultra sensitive NO2 detection
      Pearce, R.; Iakimov, T.; Andersson, M.; Hultman, L.; Spetz, A. Lloyd; Yakimova, R.
      Sensors and Actuators, B: Chemical (2011), 155 (2), 451-455CODEN: SABCEB; ISSN:0925-4005. (Elsevier B.V.)
      Epitaxially grown single layer and multilayer graphene on SiC devices were fabricated and compared for response towards NO2. Due to electron donation from SiC, single layer graphene is n-type with a very low carrier concn. The choice of substrate is demonstrated to enable tailoring of the electronic properties of graphene, with a SiC substrate realizing simple resistive devices tuned for extremely sensitive NO2 detection. The gas exposed uppermost layer of the multi layer device is screened from the SiC by the intermediate layers leading to a p-type nature with a higher concn. of charge carriers and therefore, a lower gas response. The single layer graphene device is thought to undergo an n-p transition upon exposure to increasing concns. of NO2 indicated by a change in response direction. This transition is likely to be due to the transfer of electrons to NO2 making holes the majority carriers.
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    22. 22
      Nallon, E. C.; Schnee, V. P.; Bright, C.; Polcha, M. P.; Li, Q. Chemical Discrimination with an Unmodified Graphene Chemical Sensor. ACS Sens. 2016, 1 (1), 26– 31,  DOI: 10.1021/acssensors.5b00029
      22
      Chemical discrimination with an unmodified graphene chemical sensor
      Nallon, Eric C.; Schnee, Vincent P.; Bright, Collin; Polcha, Michael P.; Li, Qiliang
      ACS Sensors (2016), 1 (1), 26-31CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
      A graphene chem. vapor sensor with an unmodified surface has been fabricated and thoroughly characterized upon exposure to headspace vapor of a variety of solvents and related compds. The vapor sensor exhibits excellent discrimination towards a variety of chem. compds. Principle component anal. (PCA) was performed to explore the extent of grouping for each compd. and sepn. between compds. and chem. classes. The prediction accuracy of the sensor is evaluated with linear discrimination anal., k-nearest neighbor, random forest, and support vector classifiers. The combination of PCA and prediction accuracies demonstrate the discrimination capability of an unmodified graphene chem. vapor sensor. Such a vapor sensor is very attractive for application in small, low-power, robust, and adaptable cross-reactive arrays in electronic noses.
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    23. 23
      Capman, N. S. S.; Zhen, X. V.; Nelson, J. T.; Chaganti, V. R. S. K.; Finc, R. C.; Lyden, M. J.; Williams, T. L.; Freking, M.; Sherwood, G. J.; Bühlmann, P.; Hogan, C. J.; Koester, S. J. Machine Learning-Based Rapid Detection of Volatile Organic Compounds in a Graphene Electronic Nose. ACS Nano 2022, 16 (11), 19567– 19583,  DOI: 10.1021/acsnano.2c10240
      There is no corresponding record for this reference.
    24. 24
      Jung, H.; Park, J. Real-Time Detection of Methyl Salicylate Vapor Using Reduced Graphene Oxide and Poly (Diallyldimethylammonium Chloride) Complex. Chem. Phys. Lett. 2022, 793, 139446  DOI: 10.1016/j.cplett.2022.139446
      24
      Real-time detection of methyl salicylate vapor using reduced graphene oxide and poly (diallyldimethylammonium chloride) complex
      Jung, Hanyung; Park, Jinhyuk
      Chemical Physics Letters (2022), 793 (), 139446CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      We report the detection of Me salicylate (MeSA) vapor with reduced graphene oxide (rGO) and a poly (diallyldimethylammonium chloride) (PDADMAC) complex. The complex was based on a graphene oxide aq. soln. where PDADMAC was dispersed and dried via photo-thermal redn. through laser irradn. to form the rGO-PDADMAC complex as a sensing matrix with a higher affinity to the target analyte, MeSA vapor. The sensor based on the rGO-PDADMAC complex was used to measure the change in resistance in real time. The rGO-PDADMAC sensor detected 11% resistance variation induced by 14.5-ppmv MeSA vapor over 540 s, while the pristine rGO sensor indicated only 1.2% resistance variation.
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    25. 25
      Lu, Y.; Goldsmith, B. R.; Kybert, N. J.; Johnson, A. T. C. DNA-Decorated Graphene Chemical Sensors. Appl. Phys. Lett. 2010, 97 (8), 083107  DOI: 10.1063/1.3483128
      25
      DNA-decorated graphene chemical sensors
      Lu, Ye; Goldsmith, B. R.; Kybert, N. J.; Johnson, A. T. C.
      Applied Physics Letters (2010), 97 (8), 083107/1-083107/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      Graphene is a two-dimensional material with exceptional electronic properties and enormous potential for applications. Graphene's promise as a chem. sensor material was noted but there was little work on practical chem. sensing using graphene, and in particular, how chem. functionalization may be used to sensitize graphene to chem. vapors. Here the authors show one route towards improving the ability of graphene to work as a chem. sensor by using single stranded DNA as a sensitizing agent. The resulting devices show fast response times, complete and rapid recovery to baseline at room temp., and discrimination between several similar vapor analytes. (c) 2010 American Institute of Physics.
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    26. 26
      Quellmalz, A.; Smith, A. D.; Elgammal, K.; Fan, X.; Delin, A.; Östling, M.; Lemme, M.; Gylfason, K. B.; Niklaus, F. Influence of Humidity on Contact Resistance in Graphene Devices. ACS Appl. Mater. Interfaces 2018, 10 (48), 41738– 41746,  DOI: 10.1021/acsami.8b10033
      There is no corresponding record for this reference.
    27. 27
      Hayasaka, T.; Lin, A.; Copa, V. C.; Lopez, L. P., Jr; Loberternos, R. A.; Ballesteros, L. I. M.; Kubota, Y.; Liu, Y.; Salvador, A. A.; Lin, L. An Electronic Nose Using a Single Graphene FET and Machine Learning for Water, Methanol, and Ethanol. Microsyst. Nanoeng. 2020, 6, 50,  DOI: 10.1038/s41378-020-0161-3
      27
      An electronic nose using a single graphene FET and machine learning for water, methanol, and ethanol
      Hayasaka, Takeshi; Lin, Albert; Copa, Vernalyn C.; Lopez Jr., Lorenzo P.; Loberternos, Regine A.; Ballesteros, Laureen Ida M.; Kubota, Yoshihiro; Liu, Yumeng; Salvador, Arnel A.; Lin, Liwei
      Microsystems & Nanoengineering (2020), 6 (1), 50CODEN: MNIACT; ISSN:2055-7434. (Nature Research)
      Abstr.: The poor gas selectivity problem has been a long-standing issue for miniaturized chem.-resistor gas sensors. The electronic nose (e-nose) was proposed in the 1980s to tackle the selectivity issue, but it required top-down chem. functionalization processes to deposit multiple functional materials. Here, we report a novel gas-sensing scheme using a single graphene field-effect transistor (GFET) and machine learning to realize gas selectivity under particular conditions by combining the unique properties of the GFET and e-nose concept. Instead of using multiple functional materials, the gas-sensing cond. profiles of a GFET are recorded and decoupled into four distinctive phys. properties and projected onto a feature space as 4D output vectors and classified to differentiated target gases by using machine-learning analyses. Our single-GFET approach coupled with trained pattern recognition algorithms was able to classify water, methanol, and ethanol vapors with high accuracy quant. when they were tested individually. Furthermore, the gas-sensing patterns of methanol were qual. distinguished from those of water vapor in a binary mixt. condition, suggesting that the proposed scheme is capable of differentiating a gas from the realistic scenario of an ambient environment with background humidity. As such, this work offers a new class of gas-sensing schemes using a single GFET without multiple functional materials toward miniaturized e-noses.
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    28. 28
      Cengiz, N.; Guclu, G.; Kelebek, H.; Capanoglu, E.; Selli, S. Application of Molecularly Imprinted Polymers for the Detection of Volatile and Off-Odor Compounds in Food Matrices. ACS Omega 2022, 7 (18), 15258– 15266,  DOI: 10.1021/acsomega.1c07288
      28
      Application of Molecularly Imprinted Polymers for the Detection of Volatile and Off-Odor Compounds in Food Matrices
      Cengiz, Nurten; Guclu, Gamze; Kelebek, Hasim; Capanoglu, Esra; Selli, Serkan
      ACS Omega (2022), 7 (18), 15258-15266CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)
      A review. Molecularly imprinted polymers (MIPs) are synthetic receptors having specific cavities intended for a template mol. with a retention mechanism that depends on mol. recognition of the targeted constituent. They were initially established for the detection of minor mols. including drugs, pesticides, or pollutants. One of the most remarkable areas where MIPs have potential utilization is in food anal., esp. in terms of volatile compds. which are found in very low concns. in foods but play a crucial role for consumer preference and acceptance. In recent years, these polymers have been used extensively for sensing volatile org. and off-odor compds. in terms of food quality for selective high-extn. purposes. This review first summarizes the basic principles and prodn. processes of MIPs. Second, their recent applications in the sepn., identification, and quantification of volatile and off-odor compds. in food samples are elucidated.
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    29. 29
      Cui, Y.; Kim, S. N.; Naik, R. R.; McAlpine, M. C. Biomimetic Peptide Nanosensors. Acc. Chem. Res. 2012, 45 (5), 696– 704,  DOI: 10.1021/ar2002057
      There is no corresponding record for this reference.
    30. 30
      Kotlowski, C.; Larisika, M.; Guerin, P. M.; Kleber, C.; Kröber, T.; Mastrogiacomo, R.; Nowak, C.; Pelosi, P.; Schütz, S.; Schwaighofer, A.; Knoll, W. Fine Discrimination of Volatile Compounds by Graphene-Immobilized Odorant-Binding Proteins. Sens. Actuators B Chem. 2018, 256, 564– 572,  DOI: 10.1016/j.snb.2017.10.093
      There is no corresponding record for this reference.
    31. 31
      Lee, K.; Yoo, Y. K.; Chae, M.-S.; Hwang, K. S.; Lee, J.; Kim, H.; Hur, D.; Lee, J. H. Highly Selective Reduced Graphene Oxide (RGO) Sensor Based on a Peptide Aptamer Receptor for Detecting Explosives. Sci. Rep. 2019, 9 (1), 10297,  DOI: 10.1038/s41598-019-45936-z
      31
      Highly selective reduced graphene oxide (rGO) sensor based on a peptide aptamer receptor for detecting explosives
      Lee Kyungjae; Yoo Yong Kyoung; Lee Junwoo; Kim Hyungsuk; Hur Don; Lee Jeong Hoon; Chae Myung-Sic; Hwang Kyo Seon
      Scientific reports (2019), 9 (1), 10297 ISSN:.
      An essential requirement for bio/chemical sensors and electronic nose systems is the ability to detect the intended target at room temperature with high selectivity. We report a reduced graphene oxide (rGO)-based gas sensor functionalized with a peptide receptor to detect dinitrotoluene (DNT), which is a byproduct of trinitrotoluene (TNT). We fabricated the multi-arrayed rGO sensor using spin coating and a standard microfabrication technique. Subsequently, the rGO was subjected to photolithography and an etching process, after which we prepared the DNT-specific binding peptide (DNT-bp, sequence: His-Pro-Asn-Phe-Se r-Lys-Tyr-IleLeu-HisGln-Arg-Cys) and DNT non-specific binding peptide (DNT-nbp, sequence: Thr-Ser-Met-Leu-Leu-Met-Ser-Pro-Lys-His-Gln-Ala-Cys). These two peptides were prepared to function as highly specific and highly non-specific (for the control experiment) peptide receptors, respectively. By detecting the differential signals between the DNT-bp and DNT-nbp functionalized rGO sensor, we demonstrated the ability of 2,4-dinitrotoluene (DNT) targets to bind to DNT-specific binding peptide surfaces, showing good sensitivity and selectivity. The advantage of using the differential signal is that it eliminates unwanted electrical noise and/or environmental effects. We achieved sensitivity of 27 ± 2 × 10(-6) per part per billion (ppb) for the slope of resistance change versus DNT gas concentration of 80, 160, 240, 320, and 480 ppm, respectively. By sequentially flowing DNT vapor (320 ppb), acetone (100 ppm), toluene (1 ppm), and ethanol (100 ppm) onto the rGO sensors, the change in the signal of rGO in the presence of DNT gas is 6400 × 10(-6) per ppb whereas the signals from the other gases show no changes, representing highly selective performance. Using this platform, we were also able to regenerate the surface by simply purging with N2.
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    32. 32
      Park, S. J.; Kwon, O. S.; Lee, S. H.; Song, H. S.; Park, T. H.; Jang, J. Ultrasensitive Flexible Graphene Based Field-Effect Transistor (FET)-Type Bioelectronic Nose. Nano Lett. 2012, 12 (10), 5082– 5090,  DOI: 10.1021/nl301714x
      32
      Ultrasensitive Flexible Graphene Based Field-Effect Transistor (FET)-Type Bioelectronic Nose
      Park, Seon Joo; Kwon, Oh Seok; Lee, Sang Hun; Song, Hyun Seok; Park, Tai Hyun; Jang, Jyongsik
      Nano Letters (2012), 12 (10), 5082-5090CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Rapid and precise discrimination of various odorants is vital to fabricating enhanced sensing devices in the fields of disease diagnostics, food safety, and environmental monitoring. Here, we demonstrate an ultrasensitive and flexible field-effect transistor (FET) olfactory system, namely, a bioelectronic nose (B-nose), based on plasma-treated bilayer graphene conjugated with an olfactory receptor. The stable p- and n-type behaviors from modified bilayer graphene (MBLG) took place after controlled oxygen and ammonia plasma treatments. It was integrated with human olfactory receptors 2AG1 (hOR2AG1: OR), leading to the formation of the liq.-ion gated FET-type platform. ORs bind to the particular odorant amyl butyrate (AB), and their interactions are specific and selective. The B-noses behave as flexible and transparent sensing devices and can recognize a target odorant with single-carbon-atom resoln. The B-noses are ultrasensitive and highly selective toward AB. The min. detection limit (MDL) is as low as 0.04 fM (10-15; signal-to-noise: 4.2), and the equil. consts. of OR-oxygen plasma-treated graphene (OR-OG) and ammonia plasma-treated graphene (-NG) are ca. 3.44 × 1014 and 1.47 × 1014 M-1, resp. Addnl., the B-noses have long-term stability and excellent mech. bending durability in flexible systems.
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    33. 33
      Kwon, O. S.; Song, H. S.; Park, S. J.; Lee, S. H.; An, J. H.; Park, J. W.; Yang, H.; Yoon, H.; Bae, J.; Park, T. H.; Jang, J. An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell. Nano Lett. 2015, 15 (10), 6559– 6567,  DOI: 10.1021/acs.nanolett.5b02286
      33
      An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell
      Kwon, Oh Seok; Song, Hyun Seok; Park, Seon Joo; Lee, Seung Hwan; An, Ji Hyun; Park, Jin Wook; Yang, Heehong; Yoon, Hyeonseok; Bae, Joonwon; Park, Tai Hyun; Jang, Jyongsik
      Nano Letters (2015), 15 (10), 6559-6567CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Human sensory-mimicking systems, such as electronic brains, tongues, skin, and ears, have been promoted for use in improving social welfare. However, no significant achievements have been made in mimicking the human nose due to the complexity of olfactory sensory neurons. Combinational coding of human olfactory receptors (hORs) is essential for odorant discrimination in mixts., and the development of hOR-combined multiplexed systems has progressed slowly. Here, the authors report the first demonstration of an artificial multiplexed superbioelectronic nose (MSB-nose) that mimics the human olfactory sensory system, leading to high-performance odorant discriminatory ability in mixts. Specifically, portable MSB-noses were constructed using highly uniform graphene micropatterns (GMs) that were conjugated with two different hORs, which were employed as transducers in a liq.-ion gated field-effect transistor (FET). Field-induced signals from the MSB-nose were monitored and provided high sensitivity and selectivity toward target odorants (min. detectable level: 0.1 fM). More importantly, the potential of the MSB-nose as a tool to encode hOR combinations was demonstrated using principal component anal.
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    34. 34
      Wasilewski, T.; Neubauer, D.; Kamysz, W.; Gębicki, J. Recent Progress in the Development of Peptide-Based Gas Biosensors for Environmental Monitoring. Case Studies in Chemical and Environmental Engineering 2022, 5, 100197  DOI: 10.1016/j.cscee.2022.100197
      There is no corresponding record for this reference.
    35. 35
      Homma, C.; Tsukiiwa, M.; Noguchi, H.; Tanaka, M.; Okochi, M.; Tomizawa, H.; Sugizaki, Y.; Isobayashi, A.; Hayamizu, Y. Designable Peptides on Graphene Field-Effect Transistors for Selective Detection of Odor Molecules. Biosens. Bioelectron. 2023, 224, 115047  DOI: 10.1016/j.bios.2022.115047
      35
      Designable peptides on graphene field-effect transistors for selective detection of odor molecules
      Homma, Chishu; Tsukiiwa, Mirano; Noguchi, Hironaga; Tanaka, Masayoshi; Okochi, Mina; Tomizawa, Hideyuki; Sugizaki, Yoshiaki; Isobayashi, Atsunobu; Hayamizu, Yuhei
      Biosensors & Bioelectronics (2023), 224 (), 115047CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
      Gas sensing based on graphene field-effect transistors (GFETs) has gained broad interest due to their high sensitivity. Further progress in gas sensing with GFETs requires to detection of various odor mols. for applications in the environmental monitoring, healthcare, food, and cosmetic industries. To develop the ubiquitous odor-sensing system, establishing an artificial sense of smell with electronic devices by mimicking olfactory receptors will be key. Although the application of olfactory receptors to GFETs is straightforward for odor sensing, synthetic mols. with a similar function to olfactory receptors would be desirable to realize the robust performance of sensing. In this work, we designed three new peptides consisting of two domains: a bio-probe to the target mols. and a mol. scaffold. These peptides were rationally designed based on a motif sequence in olfactory receptors and self-assembled into a mol. thin film on GFETs. Limonene, Me salicylate, and menthol were employed as representative odor mols. of plant flavors to demonstrate the biosensing of odor mols. The cond. change of GFETs against the binding to odor mols. with various concns. and the dynamic response revealed a distinct signature of three different peptides against individual species of the target mols. The kinetic response of each peptide exhibited characteristic time consts. in the adsorption and desorption process, also supported by the principal component anal. Our demonstration of the graphene odor sensors with the designed peptides opens a way to establish future peptide-array sensors with multi-sequence of peptide, realizing an odor sensing system with higher selectivity.
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    36. 36
      Bartošík, M.; Mach, J.; Piastek, J.; Nezval, D.; Konečný, M.; Švarc, V.; Ensslin, K.; Šikola, T. Mechanism and Suppression of Physisorbed-Water-Caused Hysteresis in Graphene FET Sensors. ACS Sens 2020, 5 (9), 2940– 2949,  DOI: 10.1021/acssensors.0c01441
      There is no corresponding record for this reference.
    37. 37
      Li, P.; Sakuma, K.; Tsuchiya, S.; Sun, L.; Hayamizu, Y. Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing. ACS Appl. Mater. Interfaces 2019, 11 (23), 20670– 20677,  DOI: 10.1021/acsami.9b04079
      37
      Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing
      Li, Peiying; Sakuma, Kouhei; Tsuchiya, Shohei; Sun, Linhao; Hayamizu, Yuhei
      ACS Applied Materials & Interfaces (2019), 11 (23), 20670-20677CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Self-assembled peptides have revealed uniform ordering on two-dimensional (2D) materials such as mica, graphene, and MoS2 so far. These peptides are expected to be utilized as a mol. scaffold for biosensing based on 2D materials. However, the stability of the peptide structures on 2D materials under liq. has not been evaluated, and some of the previously reported peptides may have instability under water. In this work, by mimicking an amino-acid sequence of silk protein, we successfully developed peptide sequences that can maintain ordered nanostructures even after rinsing with DI water. The structural stability was also proven under electrochem. bias, which is crucial as a biomol. scaffold for practical biosensing with 2D materials. The stability probably arises from its β-sheet like structures with improved intermol. interactions and binding to the surface of 2D materials, resulting in the formation of stable domains of ordered peptide structures. Our peptides showed its ability to immobilize probe mols. for biosensing and inhibit a non-specific adsorption through its co-assembly process. Interestingly, we found that two structural phases in the self-assembled structures, where only one of the phases reveals a binding affinity to target mols.
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    38. 38
      Rungreungthanapol, T.; Homma, C.; Akagi, K.-I.; Tanaka, M.; Kikuchi, J.; Tomizawa, H.; Sugizaki, Y.; Isobayashi, A.; Hayamizu, Y.; Okochi, M. Volatile Organic Compound Detection by Graphene Field-Effect Transistors Functionalized with Fly Olfactory Receptor Mimetic Peptides. Anal. Chem. 2023, 95 (9), 4556– 4563,  DOI: 10.1021/acs.analchem.3c00052
      There is no corresponding record for this reference.
    39. 39
      Noguchi, H.; Nakamura, Y.; Tezuka, S.; Seki, T.; Yatsu, K.; Narimatsu, T.; Nakata, Y.; Hayamizu, Y. Self-Assembled GA-Repeated Peptides as a Biomolecular Scaffold for Biosensing with MoS2 Electrochemical Transistors. ACS Appl. Mater. Interfaces 2023, 15 (11), 14058– 14066,  DOI: 10.1021/acsami.2c23227
      There is no corresponding record for this reference.
    40. 40
      Vosshall, L. B.; Wong, A. M.; Axel, R. An Olfactory Sensory Map in the Fly Brain. Cell 2000, 102 (2), 147– 159,  DOI: 10.1016/S0092-8674(00)00021-0
      There is no corresponding record for this reference.
    41. 41
      Dweck, H. K. M.; Ebrahim, S. A. M.; Kromann, S.; Bown, D.; Hillbur, Y.; Sachse, S.; Hansson, B. S.; Stensmyr, M. C. Olfactory Preference for Egg Laying on Citrus Substrates in Drosophila. Curr. Biol. 2013, 23 (24), 2472– 2480,  DOI: 10.1016/j.cub.2013.10.047
      There is no corresponding record for this reference.
    42. 42
      Dweck, H. K. M.; Ebrahim, S. A. M.; Retzke, T.; Grabe, V.; Weißflog, J.; Svatoš, A.; Hansson, B. S.; Knaden, M. The Olfactory Logic behind Fruit Odor Preferences in Larval and Adult Drosophila. Cell Rep. 2018, 23 (8), 2524– 2531,  DOI: 10.1016/j.celrep.2018.04.085
      There is no corresponding record for this reference.
    43. 43
      Yavari, F.; Kritzinger, C.; Gaire, C.; Song, L.; Gulapalli, H.; Borca-Tasciuc, T.; Ajayan, P. M.; Koratkar, N. Tunable Bandgap in Graphene by the Controlled Adsorption of Water Molecules. Small 2010, 6 (22), 2535– 2538,  DOI: 10.1002/smll.201001384
      43
      Tunable Bandgap in Graphene by the Controlled Adsorption of Water Molecules
      Yavari, Fazel; Kritzinger, Christo; Gaire, Churamani; Song, Li; Gulapalli, Hemtej; Borca-Tasciuc, Theodorian; Ajayan, Pulickel M.; Koratkar, Nikhil
      Small (2010), 6 (22), 2535-2538CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A facile technique to open a bandgap in graphene based on water adsorption to the graphene surface is reported. An environmental chamber with precise control of the abs. humidity level is used to control the amt. of water adsorbed to the graphene surface. This technique does not require any complicated engineering or modification of the graphene surface and does not rely on chem. doping or defect generation. However, the device will have to be equipped with an enclosure to precisely control the humidity levels. The hydration of the graphene film can be tuned by controlling the abs. humidity level of the environment.
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    44. 44
      Levesque, P. L.; Sabri, S. S.; Aguirre, C. M.; Guillemette, J.; Siaj, M.; Desjardins, P.; Szkopek, T.; Martel, R. Probing Charge Transfer at Surfaces Using Graphene Transistors. Nano Lett. 2011, 11 (1), 132– 137,  DOI: 10.1021/nl103015w
      44
      Probing Charge Transfer at Surfaces Using Graphene Transistors
      Levesque, Pierre L.; Sabri, Shadi S.; Aguirre, Carla M.; Guillemette, Jonathan; Siaj, Mohamed; Desjardins, Patrick; Szkopek, Thomas; Martel, Richard
      Nano Letters (2011), 11 (1), 132-137CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Graphene field effect transistors (FETs) are extremely sensitive to gas exposure. Charge transfer doping of graphene FETs by atm. gas is ubiquitous but not yet understood. We have used graphene FETs to probe minute changes in electrochem. potential during high-purity gas exposure expts. Our study shows quant. that electrochem. involving adsorbed water, graphene, and the substrate is responsible for doping. We not only identify the water/oxygen redox couple as the underlying mechanism but also capture the kinetics of this reaction. The graphene FET is highlighted here as an extremely sensitive potentiometer for probing electrochem. reactions at interfaces, arising from the unique d. of states of graphene. This work establishes a fundamental basis on which new electrochem. nanoprobes and gas sensors can be developed with graphene.
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    45. 45
      Smith, A. D.; Elgammal, K.; Niklaus, F.; Delin, A.; Fischer, A. C.; Vaziri, S.; Forsberg, F.; Råsander, M.; Hugosson, H.; Bergqvist, L.; Schröder, S.; Kataria, S.; Östling, M.; Lemme, M. C. Resistive Graphene Humidity Sensors with Rapid and Direct Electrical Readout. Nanoscale 2015, 7 (45), 19099– 19109,  DOI: 10.1039/C5NR06038A
      45
      Resistive graphene humidity sensors with rapid and direct electrical readout
      Smith, Anderson D.; Elgammal, Karim; Niklaus, Frank; Delin, Anna; Fischer, Andreas C.; Vaziri, Sam; Forsberg, Fredrik; Raasander, Mikael; Hugosson, Haakan; Bergqvist, Lars; Schroeder, Stephan; Kataria, Satender; Oestling, Mikael; Lemme, Max C.
      Nanoscale (2015), 7 (45), 19099-19109CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      We demonstrate humidity sensing using a change of the elec. resistance of single-layer chem. vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atm. pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. D. functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO2 substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct elec. readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.
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    46. 46
      Bampoulis, P.; Sotthewes, K.; Dollekamp, E.; Poelsema, B. Water Confined in Two-Dimensions: Fundamentals and Applications. Surf. Sci. Rep. 2018, 73 (6), 233– 264,  DOI: 10.1016/j.surfrep.2018.09.001
      46
      Water confined in two-dimensions: Fundamentals and applications
      Bampoulis, Pantelis; Sotthewes, Kai; Dollekamp, Edwin; Poelsema, Bene
      Surface Science Reports (2018), 73 (6), 233-264CODEN: SSREDI; ISSN:0167-5729. (Elsevier B.V.)
      A review. The behavior of water in close proximity to other materials under ambient conditions is of great significance due to its importance in a broad range of daily applications and scientific research. The structure and dynamics of water at an interface or in a nanopore are often significantly different from those of its bulk counterpart. Until recently, exptl. access to these interfacial water structures was difficult to realize. The advent of two-dimensional materials, esp. graphene, and the availability of various scanning probe microscopies were instrumental to visualize, characterize and provide fundamental knowledge of confined water. This review article summarizes the recent exptl. and theor. progress in a better understanding of water confined between layered Van der Waals materials. These results reveal that the structure and stability of the hydrogen bonded networks are detd. by the elegant balance between water-surface and water-water interactions. The water-surface interactions often lead to structures that differ significantly from the conventional bilayer model of natural ice. Here, we review the current knowledge of water adsorption in different environments and intercalation within various confinements. In addn., we extend this review to cover the influence of interfacial water on the two-dimensional material cover and summarize the use of these systems in potential novel applications. Finally, we discuss emerged issues and identify some flaws in the present understanding.
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    47. 47
      Shang, X.; Park, C. H.; Jung, G. Y.; Kwak, S. K.; Oh, J. H. Highly Enantioselective Graphene-Based Chemical Sensors Prepared by Chiral Noncovalent Functionalization. ACS Appl. Mater. Interfaces 2018, 10 (42), 36194– 36201,  DOI: 10.1021/acsami.8b13517
      47
      Highly Enantioselective Graphene-Based Chemical Sensors Prepared by Chiral Noncovalent Functionalization
      Shang, Xiaobo; Park, Cheol Hee; Jung, Gwan Yeong; Kwak, Sang Kyu; Oh, Joon Hak
      ACS Applied Materials & Interfaces (2018), 10 (42), 36194-36201CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      As a basic characteristic of the natural environment and living matter, chirality was used in various scientific and technol. fields. Chiral discrimination is of particular interest owing to its importance in catalysis, org. synthesis, biomedicine, and pharmaceutics. However, it is still very challenging to effectively and selectively sense and sep. different enantiomers. Here, enantio-differentiating chemosensor systems were developed through spontaneous chiral functionalization of the surface of graphene field-effect transistors (GFETs). GFET sensors functionalized using noncovalent interactions between graphene and a newly synthesized chiral-functionalized pyrene material, Boc-L-Phe-Pyrene, exhibit highly enantioselective detection of natural acryclic monoterpenoid enantiomers, i.e., (R)-(+)- and (S)-(-)-β-citronellol. From a computational study, the origin of enantio-differentiation is assigned to the discriminable charge transfer from (R)-(+)- or (S)-(-)-β-citronellol into graphene with a significant difference in binding strength depending on surface morphol. The chemosensor system developed herein has great potential to be applied in miniaturized and rapid enantioselective sensing with high sensitivity and selectivity.
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    48. 48
      Practical Guide to Chemometrics, Second Edition, 2nd ed.; Gemperline, P., Ed.; CRC Press: Boca Raton, FL, 2006.
      There is no corresponding record for this reference.
    49. 49
      Li, D.; Zhu, B.; Pang, K.; Zhang, Q.; Qu, M.; Liu, W.; Fu, Y.; Xie, J. Virtual Sensor Array Based on Piezoelectric Cantilever Resonator for Identification of Volatile Organic Compounds. ACS Sens 2022, 7 (5), 1555– 1563,  DOI: 10.1021/acssensors.2c00442
      49
      Virtual Sensor Array Based on Piezoelectric Cantilever Resonator for Identification of Volatile Organic Compounds
      Li, Dongsheng; Zhu, Boyi; Pang, Kai; Zhang, Qian; Qu, Mengjiao; Liu, Weiting; Fu, YongQing; Xie, Jin
      ACS Sensors (2022), 7 (5), 1555-1563CODEN: ASCEFJ; ISSN:2379-3694. (American Chemical Society)
      Piezoelec. cantilever resonator is one of the most promising platforms for real-time sensing of volatile org. compds. (VOCs). However, it has been a great challenge to eliminate the cross-sensitivity of various VOCs for these cantilever-based VOC sensors. Herein, a virtual sensor array (VSA) is proposed on the basis of a sensing layer of GO film deposited onto an AlN piezoelec. cantilever with five groups of top electrodes for identification of various VOCs. Different groups of top electrodes are applied to obtain high amplitudes of multiple resonance peaks for the cantilever, thus achieving low limits of detection (LODs) to VOCs. Frequency shifts of multiple resonant modes and changes of impedance values are taken as the responses of the proposed VSA to VOCs, and these multidimensional responses generate a unique fingerprint for each VOC. On the basis of machine learning algorithms, the proposed VSA can accurately identify different types of VOCs and mixts. with accuracies of 95.8 and 87.5%, resp. Furthermore, the VSA has successfully been applied to identify the emissions from healthy plants and "plants with late blight" with an accuracy of 89%. The high levels of identifications show great potentials of the VSA for diagnosis of infectious plant diseases by detecting VOC biomarkers.
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    50. 50
      Lambert, N.; Chen, Y.-N.; Cheng, Y.-C.; Li, C.-M.; Chen, G.-Y.; Nori, F. Quantum Biology. Nat. Phys. 2013, 9 (1), 10– 18,  DOI: 10.1038/nphys2474
      50
      Quantum biology
      Lambert, Neill; Chen, Yueh-Nan; Cheng, Yuan-Chung; Li, Che-Ming; Chen, Guang-Yin; Nori, Franco
      Nature Physics (2013), 9 (1), 10-18CODEN: NPAHAX; ISSN:1745-2473. (Nature Publishing Group)
      A review. Recent evidence suggests that a variety of organisms may harness some of the unique features of quantum mechanics to gain a biol. advantage. These features go beyond trivial quantum effects and may include harnessing quantum coherence on physiol. important timescales. In this brief review the authors summarize the latest results for non-trivial quantum effects in photosynthetic light harvesting, avian magnetoreception and several other candidates for functional quantum biol. We present both the evidence for and arguments against there being a functional role for quantum coherence in these systems.
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    51. 51
      Nakano-Baker, O.; Fong, H.; Shukla, S.; Lee, R. V.; Cai, L.; Godin, D.; Hennig, T.; Rath, S.; Novosselov, I.; Dogan, S.; Sarikaya, M.; MacKenzie, J. D. Data-Driven Design of a Multiplexed, Peptide-Sensitized Transistor to Detect Breath VOC Markers of COVID-19. Biosens. Bioelectron. 2023, 229, 115237  DOI: 10.1016/j.bios.2023.115237
      There is no corresponding record for this reference.
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      Pedregosa, F.; Varoquaux, G.; Gramfort, A.; Michel, V.; Thirion, B.; Grisel, O.; Blondel, M.; Prettenhofer, P.; Weiss, R.; Dubourg, V.; Vanderplas, J.; Passos, A.; Cournapeau, D.; Brucher, M.; Perrot, M.; Duchesnay, E. Scikit-Learn: Machine Learning in PYthon. J. Mach. Learn. Res. 2011, 12, 2825– 2830
      There is no corresponding record for this reference.

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.4c01177.

    • Structure of the peptides on the graphite and graphene surface; homemade gas sensing system with graphene field effect transistors (GFETs); chiral recognition of limonene with peptide-functionalized GFETs; long-term observation of limonene sensing; the detection limit of limonene gas using peptide-functionalized GFETs; principal component analysis (PCA) and hierarchical cluster analysis (HCA) (PDF)


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