Nanotube Sensors Research Articles

Enhanced performance of core-shell structured polyaniline at helical carbon nanotube hybrids for ammonia gas sensor

A core-shell structured hybrid of polyaniline at helical carbon nanotubes was synthesized using in situ polymerization, which the helical carbon nanotubes were uniformly surrounded by a layer of polyaniline nanorods array. More interestingly, repeatable responses were experimentally observed that the sensitivity to ammonia gas of the as-prepared helical shaped core-shell hybrid displays an enhancement of more than two times compared to those of only polyaniline or helical carbon nanotubes sensors because of the peculiar structures with high surface area. This kind of hybrid comprising nanorod arrays of conductive polymers covering carbon nanotubes and related structures provide a potential in sensors of trace gas detection for environmental monitoring and safety forecasting.

(Invited) A Printed Carbon Nanotube Sensor on a Flexible Substrate

This work presents inkjet printing of carbon nanotubes on a flexible substrate for a sensor application. An inkjet printed carbon nanotube pattern can be used as a conductive trace or an electrode for a low-cost flexible sensor or a printable electronic device. In this work, an office inkjet printer was modified to print an ink solution made of carbon nanotubes to form conductive patterns on a flexible substrate. Preparation of aqueous carbon nanotube ink was investigated and optimized to achieve good dispersion of carbon nanotubes and high conductance of the printed carbon nanotube patterns. Electrical properties of the printed carbon nanotube pattern were also characterized with a flexible substrate. For a sensor demonstration, the printed carbon nanotube electrode was tested as a working electrode of an electrochemical cell. The results show a promising feasibility for inkjet printed sensor applications.

Synthesis of pristine In2O3/ZnO–In2O3 composited nanotubes and investigate the enhancement of their acetone sensing properties

Pristine In2O3 and ZnO–In2O3 composited nanotubes were synthesized by the electrospinning technic and followed by calcination. The formation of ZnO–In2O3 n–n heterojunctions was found to be highly sensitive to acetone gas. X-ray powder diffraction (XRD), Scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS) were respectively used to characterize surface crystallinity and morphology. The possible mechanism of nanotubes formation was also investigated. Gas sensors were made based on the as-synthesized materials to investigate their gas sensing properties. Compare with the pristine In2O3 nanotubes, ZnO–In2O3 composite nanotubes show the obviously improved of acetone sensitivity. The sensitivity of ZnO–In2O3 composite nanotubes is about 43.2, which is about triple times larger than that of the pristine In2O3 nanotubes to 60ppm acetone at 280°C. The response and recovery times of ZnO–In2O3 nanotubes to 60ppm acetone are about 5 and 25s. In addition, ZnO–In2O3 composite nanotubes sensor also possesses a good selectivity to acetone.

A Printed Carbon Nanotube Sensor on a Flexible Substrate

Printing becomes an emerging manufacturing technology for mechanics, electronics, and consumer products. Carbon nanotubes have recently been used as a material for sensors and electrodes due to their unique electrical and mechanical properties. Printed electrodes and conductive traces particularly offer versatility of fabricating low-cost, disposable, and flexible sensors and devices. While screen-printing has been a conventional method for printing conductive traces and electrodes, inkjet-printing recently attracts a wide attention due to its unique advantages including no template requirement, rapid printing at low cost, on-demand printing capability, and precise control of the printed material. Computer generated conductive trace or electrode patterns can simply be printed on a flexible substrate with proper conductive ink. However, for inkjet-printing of nanotubes to form conductive traces and electrodes, there are few challenges that need to be addressed. One is nanotube dispersion in an ink base solution while others include adjusting surface tension and controlling viscosity of the ink and treating the surface of the printing substrate. This work presents carbon nanotube ink preparation and its demonstration in chemical sensing along with our recent achievements.It is essential to disperse carbon nanotubes to make a carbon nanotube ink. In our previous work, we have demonstrated an inkjet printed electrochemical sensor using an office HP inkjet printer and a carbon nanotube ink. Sodium dodecyl sulfate (SDS) was used as a dispersant and a surfactant in preparing the carbon nanotube ink. It should be noted that that a ratio of SDS concentration and carbon nanotube concentration would be an important factor determining the sheet resistance of a printed carbon nanotube pattern. A preliminary test result confirmed that there would be an optimum SDS:CNT ratio. For flexible sensor applications, sheet resistance change of the printed carbon nanotube patterns on a flexible substrate was measured for varying curvatures of the substrate. For a curvature up to 0.36 cm-1, the sheet resistance increase was less than 2.5% showing that the printed carbon nanotube patterns could be used for a flexible and printed sensor. Using the developed technologies, a fully printed carbon nanotube sensor on a flexible substrate will be demonstrated for chemical and biological sensing.

Chemical vapor sensing of two-dimensional MoS2 field effect transistor devices

MoS2, in single to few-layer format, is of interest because of its potential for advanced transistor and sensor applications. Its sizable bandgap enables single layer transistors with large on/off current ratios, and the large surface-to-volume ratio provides sensitive transduction of surface physisorption to the channel conductivity. Here, we discuss aspects of transistor device fabrication and of chemical vapor sensing experiments. We expose MoS2 chemical sensors to a variety of analytes, find the largest response to triethylamine, a nerve gas by-product, and explain our results based on a donor–acceptor model. We show that our MoS2 sensors provide comparable sensitivity and much higher selectivity than other low-dimensional sensors such as carbon nanotube and graphene chemical sensors. We present results for back-gated sensing and light sensitivity for our monolayer MoS2 sensors, and compare the results with multilayer MoS2 sensors.

TiO2 nanotube sensor for online chemical oxygen demand determination in conjunction with flow injection technique.

A simple, rapid and environmental friendly online chemical oxygen demand (COD) analytical method based on TiO2 nanotube sensor in conjunction with the flow injection technique was proposed to determine the COD of aqueous samples, especially for refractory organics, low-concentration wastewater, and surface water. The new method can overcome the drawbacks of the conventional COD determination methods. The results show that with the new method, each analysis takes only about 1 to 3 min, the linear range is up to 1 to 500 mg x L(-1) of the compound of interest, and the detection limit is 1 mg x L(-1). The COD values obtained by the proposed method are more accurate than those obtained by the conventional method.

Carbon nanotube sensor thread for distributed strain and damage monitoring on IM7/977-3 composites

Laminated composite materials are used in applications where light weight is a key requirement. However, minor delamination damage in composites can propagate and lead to the failure of components. Failure occurs because delamination reduces the local bending stiffness and increases bending stress, which leads to the propagation of damage and eventual failure. These failures may be avoided if the damage could be detected early and repaired. Although many damage detection methods have been investigated, none are in widespread use today to prevent the failure of composites. This paper describes the use of carbon nanotube sensor thread to monitor strain and damage in composite materials. Sensor thread was bonded onto an IM7-laminated composite coupon to measure surface strain in a quasi-static uniaxial tensile test. The sensor thread was calibrated against a strain gage, which was also mounted to the coupon. The sensor thread measured the average strain over the length of the sample and indicated when the strain exceeded a nominal safe level. Sensor thread was also bonded to the surface of laminated composite panels in different patterns and detected, located and partially characterized the damage caused by multiple impacts to the panel. The new findings in this paper can be summarized as; (1) carbon nanotube sensor thread was tested as a distributed sensor for the first time on IM7/977-3 composites; (2) the sensor thread was found to monitor strain and detect damage in the composites with a potential sensitivity down to the micro-crack level; (3) the sensor thread was barely visible on the composite and did not add significant mass or affect the integrity of the composite; (4) the data acquisition system developed was simple and reliable.

Construction and Validation of New Electrochemical Carbon Nanotubes Sensors for Determination of Acebutolol Hydrochloride in Pharmaceuticals and Biological Fluids

AbstractA simple, rapid and a highly selective method for direct electrochemical determination of acebutolol hydrochloride (AC) was developed. The developed method was based on the construction of three types of sensors conventional polymer (I), carbon paste (II) and modified carbon nanotubes (MCNTs) carbon paste (III). The fabricated sensors depend mainly on the incorporation of acebutolol hydrochloride with phosphotungstic acid (PTA) forming ion exchange acebutolol‐phosphotungstate (AC‐PT). The performance characteristics of the proposed sensors were studied. The sensors exhibited Nernstian responses (55.6 ± 0.5, 57.14 ± 0.2 and 58.6 ± 0.4 mV mol L−1) at 25 °C over drug concentration ranges (1.0 × 10−6‐1.0 × 10−2, 1.0 × 10−7‐1.0 × 10−2 and 5.0 × 10−8‐1.0 × 10−2 mol L−1 with lower detection limits of (5.0 × 10−7, 5.0 × 10−8 and 2.5 × 10−8 mol L−1 for sensors (I), (II) and (III), respectively. The influence of common and possible interfering species, pharmaceutical additives and some related pharmacological action drugs was investigated using separate solution method and no interference was found. The stability indicating using forced degradation of acebutolol hydrochloride was studied. The standard addition method was used for determination of the investigated drug in its pharmaceutical dosage forms and biological fluids. The results were validated and statistically analysed and compared with those from previously reported methods.

Analysis of Sensing Mechanisms in a Gold-Decorated SWNT Network DNA Biosensor

We show that carbon nanotube sensors with gold particles on the single-walled carbon nanotube (SWNT) network operate as Schottky barrier transistors, in which transistor action occurs primarily by varying the resistance of Au-SWNT junction rather than the channel conductance modulation. Transistor characteristics are calculated for the statistically simplified geometries, and the sensing mechanisms are analyzed by comparing the simulation results of the MOSFET model and Schottky junction model with the experimental data. We demonstrated that the semiconductor MOSFET effect cannot explain the experimental phenomena such as the very low limit of detection (LOD) and the logarithmic dependence of sensitivity to the DNA concentration. By building an asymmetric oncentricelectrode model which consists of serially-connected segments of CNTFETs and Schottky diodes, we found that for a proper explanation of the experimental data, the work function shifts should be ~ 0.1 eV for 100 pM DNA concentration and ~ 0.4 eV for 100 μM.

Ni-doped TiO2 nanotubes for wide-range hydrogen sensing

Doping of titania nanotubes is one of the efficient way to obtain improved physical and chemical properties. Through electrochemical anodization and annealing treatment, Ni-doped TiO2 nanotube arrays were fabricated and their hydrogen sensing performance was investigated. The nanotube sensor demonstrated a good sensitivity for wide-range detection of both dilute and high-concentration hydrogen atmospheres ranging from 50 ppm to 2% H2. A temperature-dependent sensing from 25°C to 200°C was also found. Based on the experimental measurements and first-principles calculations, the electronic structure and hydrogen sensing properties of the Ni-doped TiO2 with an anatase structure were also investigated. It reveals that Ni substitution of the Ti sites could induce significant inversion of the conductivity type and effective reduction of the bandgap of anatase oxide. The calculations also reveal that the resistance change for Ni-doped anatase TiO2 with/without hydrogen absorption was closely related to the bandgap especially the Ni-induced impurity level.

Conducting polymer coated single-walled carbon nanotube gas sensors for the detection of volatile organic compounds.

The current work involves fabrication, characterization and subsequent evaluation of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) coated single walled carbon nanotubes (SWNTs) sensors for detecting analytes of interest in industrial manufacturing. By varying the conducting polymer׳s synthesis conditions in terms of charge controlled electropolymerization of the monomer EDOT in presence of the dopant PSS, the sensing performance of the PEDOT:PSS functionalized SWNT sensors was systematically optimized. Electrical characterization in terms of change in resistance, cyclic voltammetry and field-effect transistor measurements was performed to confirm the presence of PEDOT:PSS coating on SWNTs. The optimized sensors exhibited sensing properties over a wide dynamic range of concentrations towards saturated vapors of volatile organic compounds (VOCs) such as methanol, ethanol and methyl ethyl ketone (MEK) at room temperature. The limit of detection of this sensor was found to be 1.3%, 5.95% and 3% for saturated vapors of methanol, ethanol and methyl ethyl ketone (MEK) respectively. In terms of performance, when compared with bare SWNTs, these hybrid sensors exhibited better sensitivity. The underlying mechanism of sensing was also investigated by using them in chemFET mode of sensor configuration.

Stretchable and Flexible High-Strain Sensors Made Using Carbon Nanotubes and Graphite Films on Natural Rubber

Conventional metallic strain sensors are flexible, but they can sustain maximum strains of only ∼5%, so there is a need for sensors that can bear high strains for multifunctional applications. In this study, we report stretchable and flexible high-strain sensors that consist of entangled and randomly distributed multiwall carbon nanotubes or graphite flakes on a natural rubber substrate. Carbon nanotubes/graphite flakes were sandwiched in natural rubber to produce these high-strain sensors. Using field emission scanning electron microscopy, the morphology of the films for both the carbon nanotube and graphite sensors were assessed under different strain conditions (0% and 400% strain). As the strain was increased, the films fractured, resulting in an increase in the electrical resistance of the sensor; this change was reversible. Strains of up to 246% (graphite sensor) and 620% (carbon nanotube sensor) were measured; these values are respectively ∼50 and ∼120 times greater than those of conventional metallic strain sensors.

Ambient Temperature Carbon Nanotube Ammonia Sensor on CMOS Platform

We report here the development of a resistive single wall carbon nanotubes (SWCNTs) sensor, based on a CMOS substrate that responds at ambient temperature to ppm levels of ammonia. The power efficient CMOS micro-hotplate is a thin membrane structure and comprises metal heater with an interdigitated electrode. The SWCNTs film was prepared first by treatment with aqua regia solution, followed by washing with distilled water, and then treated with ascorbic acid at 95°C. The film was deposited by simply dipping the chip into the solution. The SWCNTs showed good response to ammonia in a humid nitrogen atmosphere.

New Validated Carbon Paste and Modified Carbon Nanotubes Sensors for Selective Determination of Pantoprazole Sodium

New Validated Carbon Paste and Modified Carbon Nanotubes Sensors for Selective Determination of Pantoprazole Sodium

A selective molecularly imprinted polymer-carbon nanotube sensor for cotinine sensing

Conductive composite films comprised of single-walled carbon nanotubes coated with molecularly imprinted poly-4-vinylphenol are produced and characterized using ultraviolet and infrared spectroscopies, confirming the successful molecular imprinting of the film with cotinine. The electrical resistance of the imprinted film changes significantly upon binding cotinine, by more than 30 kΩ, while the unimprinted film in comparison elicits little response. Additionally, once the cotinine template desorbs from the film, the resistance of the imprinted film returns to a value close to the pre-adsorption baseline. Scanning electron microscopy is used to study the morphology of the film compared with the unimprinted control, and gas chromatography quantitatively confirms that the imprinted film selectively detects cotinine while discriminating against the structurally similar alkaloid, nicotine.

Uniform, Homogenous Coatings of Carbon Nanohorns on Arbitrary Substrates from Common Solvents

We demonstrate a facile technique to electrophoretically deposit homogenous assemblies of single-walled carbon nanohorns (CNHs) from common solvents such as acetone and water onto nearly any substrate including insulators, dielectrics, and three-dimensional metal foams, in many cases without the aid of surfactants. This enables the generation of pristine film-coatings formed on time scales as short as a few seconds and on three-dimensional templates that enable the formation of freestanding polymer-CNH supported materials. As electrophoretic deposition is usually only practical on conductive electrodes, we emphasize our observation of efficient deposition on nearly any material, including nonconductive substrates. The one-step versatility of deposition on these materials provides the capability to directly assemble CNH materials onto functional surfaces for a broad range of applications. In this manner, we utilized as-deposited CNH films as conductometric gas sensors exhibiting better sensitivity in comparison to equivalent single-walled carbon nanotube sensors. This gives a route toward scalable and inexpensive solution-based processing routes to manufacture functional nanocarbon materials for catalysis, energy, and sensing applications, among others.

Performance of graphene, carbon nanotube, and gold nanoparticle chemiresistor sensors for the detection of petroleum hydrocarbons in water

The performance of chemiresistor sensors made from thin film assemblies of single-wall carbon nanotubes, multiwall carbon nanotubes, reduced graphene oxide nanosheets (RGON), and gold nanoparticles (AuNP) was assessed with an immersible microelectrode array. Carbon nanotube and RGON chemiresistors were functionalized with octadecyl-1-amine and the AuNP chemiresistors were functionalized with 1-hexanethiol. The analytes examined were aqueous solutions of petroleum hydrocarbons: cyclohexane, naphthalene, benzene, toluene, ethylbenzene, and the three isomers of xylene (BTEX analytes). Titrations were performed to determine the detection limits of the different chemiresistors. The AuNP chemiresistor was the most sensitive to all the analytes with limits of detection between 0.2 and 0.6 ppm in water. In contrast, the multiwall carbon nanotube chemiresistor was the least sensitive to the analytes with limits of detection between 20 and 200 ppm. These sensitivities show that these nanomaterials have the potential, with further optimization, of being incorporated into devices that would respond to hydrocarbons in water at concentrations relevant to the regulations of the US Environmental Protection Agency. The stability of the sensors over 26 days was also assessed. Remarkably, there was a negligible change in the electrical resistance of the RGON sensors over this time. The nanotube sensors increased in resistance and the AuNP decreased in resistance over the same period. The drifting resistances did not affect the sensitivity of the nanomaterials, which remained constant with time.

A room temperature chloroform sensor using TiO2 nanotubes

The present study proposes the use of a TiO2 nanotube array sensor for detecting chloroform at room temperature. Highly ordered TiO2 nanotubes were synthesized by using electrochemical anodization process. The sensor response toward chloroform was tested, and the results show that the TiO2 nanotube sensor array has good response and the sensor is able to desorb attached species very efficiently, and yield very promising results. Finally, the mechanism of chloroform sensing is discussed.

A Robust Low Power Carbon Nanotube Sensor Interface Circuit in 180 nm CMOS Technology

The design and performance of a low-cost, energy-efficient carbon nanotube sensor interface circuit (SIC) is presented that is aimed at deployable/expendable applications with the sensor operating at ambient temperatures. The submicrometer SIC is designed and fabricated in CMOS 180-nm technology and consumes a maximum of 122 μW, including a decoder and voltage follower. The SIC achieves a measurement accuracy of 1.4% over a 2.5 kΩ to 25 MΩ dynamic range of sensor resistance. A critical issue associated with a submicrometer integrated circuit implementation is satisfactory performance of the SIC for fabrication process variations that range from the slow, to typical, to fast process corners and simultaneously meeting the requirement for the very large dynamic range for sensor resistances. A robust design considering the full range of potential process variations becomes more critical as feature size is reduced. The SIC design includes an added degree for freedom for counteracting process variations during post fabrication calibration. In addition, a new design procedure is outlined and implemented to permit an accurate and efficient first order design to ensure satisfactory performance for typical, fast, and slow model parameters. The first order design is verified by complete model simulation performance, and finally selected measured results are included for a fabricated circuit.

Corrections to "An electromechanical system based on carbon nanotube sensors to detect apnea" [Jul 13 2737-2741

In the above paper (ibid., vol. 13, no. 7, pp. 2737-2741, Jul. 2013), a corresponding author name was omitted from the first footnote. The revised footnote is presented here.