Research

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9 pages, 1780 KiB

Open AccessArticle

A New Electro-Optical Switch Modulator Based on the Surface Plasmon Polaritons of Graphene in Mid-Infrared Band

by Ming Cai, Shulong Wang, Bo Gao, Yindi Wang, Tao Han and Hongxia Liu

Sensors 2019, 19(1), 89; https://doi.org/10.3390/s19010089 - 28 Dec 2018

Cited by 12 | Viewed by 3875

In this paper, a new electro-optical switch modulator based on the surface plasmon polaritons of graphene is proposed. An air–graphene-substrate–dielectric structure is adopted in the modulator. In this structure, the graphene is considered as a film of metal whose thickness tends to be [...] Read more.

In this paper, a new electro-optical switch modulator based on the surface plasmon polaritons of graphene is proposed. An air–graphene-substrate–dielectric structure is adopted in the modulator. In this structure, the graphene is considered as a film of metal whose thickness tends to be infinitesimal. By changing the external voltage, the boundary conditions can be changed to decide whether the surface plasmon polariton waves can be excited in mid-infrared band. Because of this effect, the structure can be used as an electro–optical switch modulator, whose modulation depth is about 100% in theory. Finally, the 3 dB bandwidth (~34 GHz) and the energy loss (36.47 fJ/bit) of the electro–optical switch modulator are given, whose low energy loss is very suitable for engineering applications. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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15 pages, 2980 KiB

Open AccessArticle

Preparation of Graphite Oxide Containing Different Oxygen-Containing Functional Groups and the Study of Ammonia Gas Sensitivity

by Liming Luo, Tongjiang Peng, Mingliang Yuan, Hongjuan Sun, Shichan Dai and Long Wang

Sensors 2018, 18(11), 3745; https://doi.org/10.3390/s18113745 - 02 Nov 2018

Cited by 32 | Viewed by 5031

Abstract

A series of graphite oxide samples were prepared using the modified Hummers method. Flake graphite was used as the raw material and the reaction temperature of the aqueous solution was changed (0 °C, 30 °C, 50 °C, 60 °C, 70 °C, 80 °C, [...] Read more.

A series of graphite oxide samples were prepared using the modified Hummers method. Flake graphite was used as the raw material and the reaction temperature of the aqueous solution was changed (0 °C, 30 °C, 50 °C, 60 °C, 70 °C, 80 °C, and 100 °C). X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectral analysis, X-ray photoelectron spectroscopy, and contact angle tests were performed to characterize the structure, chemical bonding, type, and content of oxygen-containing functional groups of the graphite oxide samples. The results showed that the type and content of each oxygen-containing functional group could be controlled by changing the reaction temperature with the addition of water. As the temperature of the system increased, the degree of oxidation of the graphite oxide samples first increased and then decreased. Too high a temperature (100 °C) of the system led to the formation of epoxy groups by the decomposition of some hydroxyl groups in the samples, causing the reduction of oxygen-containing functional groups between the graphite layers, poor hydrophilic properties, and low moisture content. When the system temperature was 50 °C, the interlayer spacing of the graphite oxide samples was at its highest, the graphite was completely oxidized (C/O = 1.85), and the oxygen-containing functional groups were mainly composed of hydroxyl groups (accounting for approximately 28.88% of the total oxygen-containing functional groups). The high content of hydroxyl and carboxyl groups had good hydrophilic ability and showed the highest moisture content. The sample at 50 °C had better sensitivity to ammonia because of its high hydroxyl group and carboxyl group content, with the sample showing an excellent profile when the ammonia concentration was 20–60 ppm. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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10 pages, 2415 KiB

Open AccessFeature PaperArticle

Reduced Graphene Oxide-Based Double Network Polymeric Hydrogels for Pressure and Temperature Sensing

by Wei Liu, Xiaoyuan Zhang, Gang Wei and Zhiqiang Su

Sensors 2018, 18(9), 3162; https://doi.org/10.3390/s18093162 - 19 Sep 2018

Cited by 20 | Viewed by 5798

Abstract

We demonstrate the fabrication of novel reduced graphene oxide (rGO)-based double network (DN) hydrogels through the polymerization of poly(N-isopropylacrylamide) (PNIPAm) and carboxymethyl chitosan (CMC). The facile synthesis of DN hydrogels includes the reduction of graphene oxide (GO) by CMC, and the [...] Read more.

We demonstrate the fabrication of novel reduced graphene oxide (rGO)-based double network (DN) hydrogels through the polymerization of poly(N-isopropylacrylamide) (PNIPAm) and carboxymethyl chitosan (CMC). The facile synthesis of DN hydrogels includes the reduction of graphene oxide (GO) by CMC, and the subsequent polymerization of PNIPAm. The presence of rGO in the fabricated PNIPAm/CMC/rGO DN hydrogels enhances the compressibility and flexibility of hydrogels with respect to pure PNIPAm hydrogels, and they exhibit favorable thermoresponsivity, compressibility, and conductivity. The created hydrogels can be continuously cyclically compressed and have excellent bending properties. Furthermore, it was found that the hydrogels are pressure- and temperature-sensitive, and can be applied to the design of both pressure and temperature sensors to detect mechanical deformation and to measure temperature. Our preliminary results suggest that these rGO-based DN hydrogels exhibit a high potential for the fabrication of soft robotics and artificially intelligent skin-like devices. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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14 pages, 3283 KiB

Open AccessArticle

Fast and Stable Ionic Electroactive Polymer Actuators with PEDOT:PSS/(Graphene–Ag-Nanowires) Nanocomposite Electrodes

by Minjeong Park, Joohee Kim, Hanjung Song, Seonpil Kim and Minhyon Jeon

Sensors 2018, 18(9), 3126; https://doi.org/10.3390/s18093126 - 16 Sep 2018

Cited by 30 | Viewed by 5415

Abstract

Ionic electroactive polymer (IEAP) actuators that are driven by electrical stimuli have been widely investigated for use in practical applications. However, conventional electrodes in IEAP actuators have a serious drawback of poor durability under long-term actuation in open air, mainly because of leakage [...] Read more.

Ionic electroactive polymer (IEAP) actuators that are driven by electrical stimuli have been widely investigated for use in practical applications. However, conventional electrodes in IEAP actuators have a serious drawback of poor durability under long-term actuation in open air, mainly because of leakage of the inner electrolyte and hydrated cations through surface cracks on the metallic electrodes. To overcome this problem, a top priority is developing new high-performance ionic polymer actuators with graphene electrodes that have superior mechanical, electrical conductivity, and electromechanical properties. However, the task is made difficultby issues such as the low electrical conductivity of graphene (G). The percolation network of silver nanowires (Ag-NWs) is believed to enhance the conductivity of graphene, while poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), which exhibits excellent stability under ambient conditions, is expected to improve the actuation performance of IEAP actuators. In this study, we developed a very fast, stable, and durable IEAP actuator by employing electrodes made of a nanocomposite comprising PEDOT:PSS and graphene–Ag-NWs (P/(G–Ag)). The cost-effective P/(G–Ag) electrodes with high electrical conductivity displayed a smooth surface resulting from the PEDOT:PSS coating, which prevented oxidation of the surface upon exposure to air, and showedstrong bonding between the ionic polymer and the electrode surface. More interestingly, the proposed IEAP actuator based on the P/G–Ag electrode can be used in active biomedical devices, biomimetic robots, wearable electronics, and flexible soft electronics. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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10 pages, 2559 KiB

Open AccessArticle

Polar Organic Gate Dielectrics for Graphene Field-Effect Transistor-Based Sensor Technology

by Kevin A. Kam, Brianne I. C. Tengan, Cody K. Hayashi, Richard C. Ordonez and David G. Garmire

Sensors 2018, 18(9), 2774; https://doi.org/10.3390/s18092774 - 23 Aug 2018

Cited by 8 | Viewed by 4930

Abstract

We have pioneered the use of liquid polar organic molecules as alternatives to rigid gate-dielectrics for the fabrication of graphene field-effect transistors. The unique high net dipole moment of various polar organic molecules allows for easy manipulation of graphene’s conductivity due to the [...] Read more.

We have pioneered the use of liquid polar organic molecules as alternatives to rigid gate-dielectrics for the fabrication of graphene field-effect transistors. The unique high net dipole moment of various polar organic molecules allows for easy manipulation of graphene’s conductivity due to the formation of an electrical double layer with a high-capacitance at the liquid and graphene interface. Here, we compare the performances of dimethyl sulfoxide (DMSO), acetonitrile, propionamide, and valeramide as polar organic liquid dielectrics in graphene field-effect transistors (GFETs). We demonstrate improved performance for a GFET with a liquid dielectric comprised of DMSO with high electron and hole mobilities of 154.0 cm²/Vs and 154.6 cm²/Vs, respectively, and a Dirac voltage <5 V. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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10 pages, 3655 KiB

Open AccessArticle

A “Turn-On” Fluorescence Copper Biosensor Based on DNA Cleavage-Dependent Graphene Oxide-dsDNA-CdTe Quantum Dots Complex

by Liyun Ding, Bing Xu, Tao Li, Jun Huang and Wei Bai

Sensors 2018, 18(8), 2605; https://doi.org/10.3390/s18082605 - 09 Aug 2018

Cited by 8 | Viewed by 3083

Abstract

A novel “turn-on” fluorescent copper biosensor is developed successfully based on the graphene oxide (GO)-dsDNA-CdTe quantum dots (QDs) complex via chemical crosslink method. The optical and structure properties of GO-dsDNA-CdTe QDs complex are studied by fluorescence (FL) spectra and transmission electron microscopy (TEM) [...] Read more.

A novel “turn-on” fluorescent copper biosensor is developed successfully based on the graphene oxide (GO)-dsDNA-CdTe quantum dots (QDs) complex via chemical crosslink method. The optical and structure properties of GO-dsDNA-CdTe QDs complex are studied by fluorescence (FL) spectra and transmission electron microscopy (TEM) in detail. It is demonstrated that the fluorescence quenching of CdTe QDs is a process of fluorescence resonance energy transfer (FRET) due to the essential surface and quenching properties of two-dimensional GO. Copper ions induce the catalytic reaction of DNA chain and irreversibly break at the cleavage site, which will cause the G-quadruplex formation, moreover further result in the CdTe QDs separated from GO and restored its fluorescence. Therefore, a significant recovery effect on the fluorescence of the GO-dsDNA-CdTe QDs complex is observed in the presence of copper ions. The fluorescence responses are concentration-dependent and can be well described by a linear equation. Compared with other metal ions, the sensor performs good selectivity for copper ions. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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13 pages, 5700 KiB

Open AccessArticle

Modifications of Au Nanoparticle-Functionalized Graphene for Sensitive Detection of Sulfanilamide

by Bao-Shan He and Xiao-Hai Yan

Sensors 2018, 18(3), 846; https://doi.org/10.3390/s18030846 - 13 Mar 2018

Cited by 18 | Viewed by 4720

Abstract

In this paper, we present a simple and feasible electrochemical sensor based on Au nanoparticle-functionalized graphene for the determination of sulfanilamide. Au nanoparticles were deposited on graphene, which acted as a platform to prepare excellent nanocomposites. Attributed to the graphene’s large surface area [...] Read more.

In this paper, we present a simple and feasible electrochemical sensor based on Au nanoparticle-functionalized graphene for the determination of sulfanilamide. Au nanoparticles were deposited on graphene, which acted as a platform to prepare excellent nanocomposites. Attributed to the graphene’s large surface area and the Au nanoparticles’ strong conductivity, many sulfanilamide molecules were enriched on the sensor surface and the signal response became more sensitive. Under the optimal conditions, the electrochemical sensors could be used for the efficient detection of sulfanilamide. Good linearity was observed in the range of 0.1–1000 μmol·L⁻¹ and the detection limit was 0.011 μmol·L⁻¹. Most importantly, the Au nanoparticle-functionalized graphene-modified electrode could be successfully applied for the detection of sulfanilamide in animal meat, and exhibited good stability, acceptable recovery, and offered a promising platform for point-of-care detecting in real samples. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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13 pages, 4061 KiB

Open AccessArticle

Preparation of Cu₂O-Reduced Graphene Nanocomposite Modified Electrodes towards Ultrasensitive Dopamine Detection

by Quanguo He, Jun Liu, Xiaopeng Liu, Guangli Li, Peihong Deng and Jing Liang

Sensors 2018, 18(1), 199; https://doi.org/10.3390/s18010199 - 12 Jan 2018

Cited by 110 | Viewed by 7341

Abstract

Cu₂O-reduced graphene oxide nanocomposite (Cu₂O-RGO) was used to modify glassy carbon electrodes (GCE), and applied for the determination of dopamine (DA). The microstructure of Cu₂O-RGO nanocomposite material was characterized by scanning electron microscope. Then the electrochemical reduction [...] Read more.

Cu₂O-reduced graphene oxide nanocomposite (Cu₂O-RGO) was used to modify glassy carbon electrodes (GCE), and applied for the determination of dopamine (DA). The microstructure of Cu₂O-RGO nanocomposite material was characterized by scanning electron microscope. Then the electrochemical reduction condition for preparing Cu₂O-RGO/GCE and experimental conditions for determining DA were further optimized. The electrochemical behaviors of DA on the bare electrode, RGO- and Cu₂O-RGO-modified electrodes were also investigated using cyclic voltammetry in phosphate-buffered saline solution (PBS, pH 3.5). The results show that the oxidation peaks of ascorbic acid (AA), dopamine (DA), and uric acid (UA) could be well separated and the peak-to-peak separations are 204 mV (AA-DA) and 144 mV (DA-UA), respectively. Moreover, the linear response ranges for the determination of 1 × 10⁻⁸ mol/L~1 × 10⁻⁶ mol/L and 1 × 10⁻⁶ mol/L~8 × 10⁻⁵ mol/L with the detection limit 6.0 × 10⁻⁹ mol/L (S/N = 3). The proposed Cu₂O-RGO/GCE was further applied to the determination of DA in dopamine hydrochloride injections with satisfactory results. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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6575 KiB

Open AccessCommunication

Room-Temperature H₂ Gas Sensing Characterization of Graphene-Doped Porous Silicon via a Facile Solution Dropping Method

by Nu Si A. Eom, Hong-Baek Cho, Yoseb Song, Woojin Lee, Tohru Sekino and Yong-Ho Choa

Sensors 2017, 17(12), 2750; https://doi.org/10.3390/s17122750 - 28 Nov 2017

Cited by 23 | Viewed by 5992

Abstract

In this study, a graphene-doped porous silicon (G-doped/p-Si) substrate for low ppm H₂ gas detection by an inexpensive synthesis route was proposed as a potential noble graphene-based gas sensor material, and to understand the sensing mechanism. The G-doped/p-Si gas sensor was synthesized [...] Read more.

In this study, a graphene-doped porous silicon (G-doped/p-Si) substrate for low ppm H₂ gas detection by an inexpensive synthesis route was proposed as a potential noble graphene-based gas sensor material, and to understand the sensing mechanism. The G-doped/p-Si gas sensor was synthesized by a simple capillary force-assisted solution dropping method on p-Si substrates, whose porosity was generated through an electrochemical etching process. G-doped/p-Si was fabricated with various graphene concentrations and exploited as a H₂ sensor that was operated at room temperature. The sensing mechanism of the sensor with/without graphene decoration on p-Si was proposed to elucidate the synergetic gas sensing effect that is generated from the interface between the graphene and p-type silicon. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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Review

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29 pages, 7325 KiB

Open AccessReview

Electrical Properties of Two-Dimensional Materials Used in Gas Sensors

by Rafael Vargas-Bernal

Sensors 2019, 19(6), 1295; https://doi.org/10.3390/s19061295 - 14 Mar 2019

Cited by 80 | Viewed by 8027

Abstract

In the search for gas sensing materials, two-dimensional materials offer the possibility of designing sensors capable of tuning the electronic band structure by controlling their thickness, quantity of dopants, alloying between different materials, vertical stacking, and the presence of gases. Through materials engineering [...] Read more.

In the search for gas sensing materials, two-dimensional materials offer the possibility of designing sensors capable of tuning the electronic band structure by controlling their thickness, quantity of dopants, alloying between different materials, vertical stacking, and the presence of gases. Through materials engineering it is feasible to study the electrical properties of two-dimensional materials which are directly related to their crystalline structure, first Brillouin zone, and dispersion energy, the latter estimated through the tight-binding model. A review of the electrical properties directly related to the crystalline structure of these materials is made in this article for the two-dimensional materials used in the design of gas sensors. It was found that most 2D sensing materials have a hexagonal crystalline structure, although some materials have monoclinic, orthorhombic and triclinic structures. Through the simulation of the mathematical models of the dispersion energy, two-dimensional and three-dimensional electronic band structures were predicted for graphene, hexagonal boron nitride (h-BN) and silicene, which must be known before designing a gas sensor. Full article

(This article belongs to the Special Issue Graphene Based Sensors and Electronics)

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