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Selectivity of Chemoresistive Sensors Made of Chemically Functionalized Carbon Nanotube Random Networks for Volatile Organic Compounds (VOC)

Author(s):Jean-François Feller -- Nicolas Gatt -- Bijandra Kumar -- Mickaël Castro
Journal: Chemosensors
Publisher:
Abstract
| Pages: 26-40
Different grades of chemically functionalized carbon nanotubes (CNT) have been processed by spraying layer-by-layer (sLbL) to obtain an array of chemoresistive transducers for volatile organic compound (VOC) detection. The sLbL process led to random networks of CNT less conductive, but more sensitive to vapors than filtration under vacuum (bucky papers). Shorter CNT were also found to be more sensitive due to the less entangled and more easily disconnectable conducting networks they are making. Chemical functionalization of the CNT’ surface is changing their selectivity towards VOC, which makes it possible to easily discriminate methanol, chloroform and tetrahydrofuran (THF) from toluene vapors after the assembly of CNT transducers into an array to make an e-nose. Interestingly, the amplitude of the CNT transducers’ responses can be enhanced by a factor of five (methanol) to 100 (chloroform) by dispersing them into a polymer matrix, such as poly(styrene) (PS), poly(carbonate) (PC) or poly(methyl methacrylate) (PMMA). COOH functionalization of CNT was found to penalize their dispersion in polymers and to decrease the sensors’ sensitivity. The resulting conductive polymer nanocomposites (CPCs) not only allow for a more easy tuning of the sensors’ selectivity by changing the chemical nature of the matrix, but they also allow them to adjust their sensitivity by changing the average gap between CNT (acting on quantum tunneling in the CNT network). Quantum resistive sensors (QRSs) appear promising for environmental monitoring and anticipated disease diagnostics that are both based on VOC analysis.

Chemo-Electrical Signal Transduction by Using Stimuli-Responsive Polymer Gate-Modified Field Effect Transistor

Author(s):Akira Matsumoto -- Yusuke Tsurui -- Hiroko Matsumoto -- Yasuhiro Maeda -- Toru Hoshi -- Takashi Sawaguchi -- Yuji Miyahara
Journal: Chemosensors
Publisher:
Abstract
| Pages: 97-107
A glucose-responsive polymer brush was designed on a gold electrode and exploited as an extended gate for a field effect transistor (FET) based biosensor. A permittivity change at the gate interface due to the change in hydration upon specific binding with glucose was detectable. The rate of response was markedly enhanced compared to the previously studied cross-linked or gel-coupled electrode, owing to its kinetics involving no process of the polymer network diffusion. This finding may offer a new strategy of the FET-based biosensors effective not only for large molecules but also for electrically neutral molecules such as glucose with improved kinetics.

A Low-Cost Fluorescent Sensor for pCO2 Measurements

Author(s):Xudong Ge -- Yordan Kostov -- Robert Henderson -- Nicholas Selock -- Govind Rao
Journal: Chemosensors
Publisher:
Abstract
| Pages: 108-120
Global warming is believed to be caused by increasing amounts of greenhouse gases (mostly CO2) discharged into the environment by human activity. In addition to an increase in environmental temperature, an increased CO2 level has also led to ocean acidification. Ocean acidification and rising temperatures have disrupted the water’s ecological balance, killing off some plant and animal species, while encouraging the overgrowth of others. To minimize the effect of global warming on local ecosystem, there is a strong need to implement ocean observing systems to monitor the effects of anthropogenic CO2 and the impacts thereof on ocean biological productivity. Here, we describe the development of a low-cost fluorescent sensor for pCO2 measurements. The detector was exclusively assembled with low-cost optics and electronics, so that it would be affordable enough to be deployed in great numbers. The system has several novel features, such as an ideal 90° separation between excitation and emission, a beam combiner, a reference photodetector, etc. Initial tests showed that the system was stable and could achieve a high resolution despite the low cost.

Luminescent Oxygen Gas Sensors Based on Nanometer-Thick Hybrid Films of Iridium Complexes and Clay Minerals

Author(s): Hisako Sato -- Kenji Tamura -- Akihiko Yamagishi
Journal: Chemosensors
Publisher:
Abstract
| Pages: 41-55
The use of Ir(III) complexes in photo-responsive molecular devices for oxygen gas sensing is reviewed. Attention is focused on the immobilization of Ir(III) complexes in organic or inorganic host materials such as polymers, silica and clays in order to enhance robustness and reliability. Our recent works on constructing nanometer-thick films comprised of cyclometalated cationic Ir(III) complexes and clay minerals are described. The achievement of multi-emitting properties in response to oxygen pressure is demonstrated.

A Method for Integrating ZnO Coated Nanosprings into a Low Cost Redox-Based Chemical Sensor and Catalytic Tool for Determining Gas Phase Reaction Kinetics

Author(s):Pavel V. Bakharev -- Vladimir V. Dobrokhotov -- David N. McIlroy
Journal: Chemosensors
Publisher:
Abstract
| Pages: 56-68
A chemical sensor (chemiresistor) was constructed from a xenon light bulb by coating it with a 3-D zinc oxide coated silica nanospring mat, where the xenon light bulb serves as the sensor heater. The sensor response to toluene as a function of xenon light bulb sensor temperature (TLB) and vapor temperature (TV) was observed and analyzed. The optimum operational parameters in terms of TLB and TV were determined to be 435 °C and 250 °C, respectively. The activation energy of toluene oxidation (Ed) on the ZnO surface was determined to be 87 kJ·mol−1, while the activation energy of oxidation (Ea) of the depleted ZnO surface was determined to be 83 kJ·mol−1. This study serves as proof of principle for integrating nanomaterials into an inexpensive sensor platform, which can also be used to characterize gas-solid, or vapor-solid, redox processes.

Equivalent Circuit Models for Determination of the Relation between the Sensing Behavior and Properties of Undoped/Cr Doped TiO2 NTs

Author(s):Yakup Gönüllü -- Klemens Kelm -- Sanjay Mathur -- Bilge Saruhan
Journal: Chemosensors
Publisher:
Abstract
| Pages: 69-84
High-temperature gas sensing requires the increase of sensitivity and reduction of cross-sensitivity. The use of TiO2-Nanotubular layers as gas sensors has shown that the selectivity and sensitivity can be influenced by doping with trivalent elements and by optimization of morphological aspects such as pore diameter and nanotube length. In this work, focus has been given on the understanding of the effect of doping and properties of nano-tubular TiO2-layers on sensing behavior and mechanism toward NO2 by using equivalent circuit modeling achieved by impedance spectroscopic measurements.

The Shell Structure Effect on the Vapor Selectivity of Monolayer-Protected Gold Nanoparticle Sensors

Author(s):Rui-Xuan Huang -- Chia-Jung Lu -- Wei-Cheng Tian
Journal: Chemosensors
Publisher:
Abstract
| Pages: 85-96
Four types of monolayer-protected gold nanoclusters (MPCs) were synthesized and characterized as active layers of vapor sensors. An interdigitated microelectrode (IDE) and quartz crystal microbalance (QCM) were used to measure the electrical resistance and mass loading changes of MPC films during vapor sorption. The vapor sensing selectivity was influenced by the ligand structure of the monolayer on the surface of gold nanoparticles. The responses of MPC-coated QCM were mainly determined according to the affinity between the vapors and surface ligands of MPCs. The responses to the resistance changes of the MPC films were due to the effectiveness of the swelling when vapor was absorbed. It was observed that resistive sensitivity to polar organics could be greatly enhanced when the MPC contained ligands that contain interior polar functional groups with exterior nonpolar groups. This finding reveals that reducing interparticle attraction by using non-polar exterior groups could increase effective swelling and therefore enhance the sensitivity of MPC-coated chemiresistors.

Synthesis, Characterization and Sensing Properties of AZO and IZO Nanomaterials

Author(s):Mokhtar Hjiri -- Lassaad El Mir -- Salvatore Gianluca Leonardi
Journal: Chemosensors
Publisher:
Abstract
| Pages: 121-130
Al-doped ZnO (AZO) and In-doped ZnO (IZO) nanopowders were prepared by a sol-gel route and subsequent drying in ethanol under supercritical conditions. The morphological and microstructural properties were investigated by transmission electron microscopy (TEM) analysis and X-ray powder diffraction (XRD). The characterization study showed that the AZO and IZO nanoparticles were crystalline and exhibited the hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the AZO and IZO nanoparticles for carbon monoxide (CO) were reported. The results indicated that both doped-sensors exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data reported.

Electrochemical Detection with Preconcentration: Nitroenergetic Contaminants

Author(s): Brandy J. Johnson -- Mansoor Nasir -- Ronald L. Siefert -- Iwona A. Leska -- Jeffrey S. Erickson -- Paul T. Charles -- Brian J. Melde -- Jenna R. Taft
Journal: Chemosensors
Publisher:
Abstract
| Pages: 131-144
This effort evaluated the potential of two prototype devices for enhanced electrochemical detection of 2,4,6-trinitrotoluene (TNT) and dinitrotoluene (DNT) following preconcentration using an organosilicate sorbent. The bench-scale prototype provides adsorption of the targets from aqueous solution followed by elution in a mixture of methanol and potassium chloride (KCl). Following elution, the eluant is diluted using an aqueous KCl solution to provide sufficient electrolyte for electrochemical analysis. Concentrations of methanol greater than 50% were detrimental to sensor performance and lifetime. Calibration of the electrochemical sensor was completed and results of electrochemical analysis were compared to those of HPLC analysis over a range of concentrations and in varied matrices. TNT detection was found to be consistent and detection limits were improved from 200 ppb to 3 ppb depending on the sample volume utilized. DNT detection showed higher variability and significantly greater false response rates. On the basis of these results, a second, more advanced, prototype was developed and utilized in limited field trials with the intention of moving the technology toward in situ applications.
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