Showing papers in "Sensors and Actuators B-chemical in 2009"

Gas sensors using hierarchical and hollow oxide nanostructures: Overview

Abstract: Hierarchical and hollow oxide nanostructures are very promising gas sensor materials due to their high surface area and well-aligned nanoporous structures with a less agglomerated configurations. Various synthetic strategies to prepare such hierarchical and hollow structures for gas sensor applications are reviewed and the principle parameters and mechanisms to enhance the gas sensing characteristics are investigated. The literature data clearly show that hierarchical and hollow nanostructures increase both the gas response and response speed simultaneously and substantially. This can be explained by the rapid and effective gas diffusion toward the entire sensing surfaces via the porous structures. Finally, the impact of highly sensitive and fast responding gas sensors using hierarchical and hollow nanostructures on future research directions is discussed.

A water-soluble cationic oligopyrene derivative : Spectroscopic studies and sensing applications

Abstract: A water-soluble cationic conjugated oligomer, oligo(2-(4-(1-pyrenyl)butanoyloxy)ethyltrimethylammonium bromide) (OPBEAB) was synthesized by the combination of chemical and electrochemical synthesis techniques. The oligomer has an average repeat unit of 4 and a high quantum yield ( Ф ) of 0.7 in an aqueous solution containing 5.91 × 10 −3 mol L −1 sodium dodecyl sulfate (SDS). In this medium, surfactant molecules formed shielding layers along the OPBEAB chains and prevented aggregation of the oligomer and also improved its fluorescence stability. The fluorescence quenching of cationic oligomer (OPBEAB) depends strongly on the mixing sequence of the probe molecule (OPBEAB), analyte (TNT), and anionic surfactant (SDS). A molecule probe based on OPBEAB can rapidly detect ultra-trace TNT in both pure aqueous solution and environmental ground water with high sensitivity. The Stern–Volmer constant ( K SV ) of the probe in aqueous solution was measured to be as high as 5.30 × 10 5 mol −1 L and the limit of detection was about 7.0 × 10 −8 mol L −1 (70 ppb) under optimized conditions.

Recent progress in the development of nano-structured conducting polymers/nanocomposites for sensor applications

Abstract: Nanomaterials of conjugated polymers are found to have superior performance relative to conventional materials due to their much larger exposed surface area. The present paper gives an overview of various recent synthetic approaches involving template free and template oriented techniques suitable for the growth of nanomaterials of conjugated polymers, their merits and application in making nanodevices. The characteristics of nano-structured conducting polymers and polymer nanocomposites, their application in sensors/biosensors and advances made in this field are reviewed.

Wireless sensor network based wearable smart shirt for ubiquitous health and activity monitoring

Abstract: The smart shirt which measures electrocardiogram (ECG) and acceleration signals for continuous and real time health monitoring is designed and developed. The shirt mainly consists of sensors for continuous monitoring the health data and conductive fabrics to get the body signal as electrodes. The measured physiological ECG data and physical activity data are transmitted in an ad-hoc network in IEEE 802.15.4 communication standard to a base-station and server PC for remote monitoring. The wearable sensor devices are designed to fit well into shirt with small size and low power consumption to reduce the battery size. The adaptive filtering method to cancel artifact noise from conductive fabric electrodes in a shirt is also designed and tested to get clear ECG signal even though during running or physical exercise of a person.

New perspectives of gas sensor technology

Abstract: Two recent topics important for advancing gas sensor technology are introduced. Semiconductor gas sensors have been developed so far on empirical bases but now a fundamental theory has been made available for further developments. The theory reveals the roles of physical properties of semiconductors and chemical properties of gases in the receptor function. MEMS techniques have been applied to fabrication of micro-platforms for use in gas sensors. The micro-platforms appear to provide gas sensors with new innovative function.

An amperometric glucose biosensor based on the immobilization of glucose oxidase on the ZnO nanotubes

Abstract: A glucose biosensor is fabricated with immobilization of glucose oxidase onto ZnO nanotube arrays by cross-linking method. The ZnO nanotube arrays are synthesized by chemical etching of ZnO nanorods that are electrochemically deposited on the Au surface. Morphology and structure of ZnO nanotubes are characterized by FESEM, HRTEM and XRD. Fourier-transform infrared spectroscopy reveals that the glucose oxidase immobilized on the ZnO nanotubes retains its native conformation. The biosensor has a wide linear range for the detection of glucose from 50 μM to 12 mM (a correlation coefficient of 0.998) with 3 s response time. The sensitivity of the biosensor is found to be 21.7 μA/mM cm 2 . Moreover, its experimental detection limit is 1 μM (S/N = 3) and the apparent Michaelis–Menten constant is calculated to be 19 mM. The anti-interference ability and long-term stability of the biosensor are also assessed. Compared with the biosensors based on the nanorod and flat structure, the proposed biosensor shows expanded linear range and sensitivity. All these results demonstrate that ZnO nanotube can provide a promising material for the biosensor designs and other biological applications.

On-chip fabrication of ZnO-nanowire gas sensor with high gas sensitivity

Abstract: ZnO-nanowire gas sensors were fabricated by a selective growth of nanowires on patterned Au catalysts thus forming nanowire air bridges or ‘nanobridges’ between two Pt pillar electrodes. The gas sensing properties of nanobridge gas sensors were demonstrated using a diluted NO2. The response, as a function of temperature, was highest at 225 °C and was linearly increased with the concentration of NO2 in the range of 0.5–3 ppm and then showed a sign of saturation. Our sensor showed higher response compared with different types of sensors including ZnO nanocrystals, Sn- and In-doped ZnO thin film, or ZnO nanowires. The enhanced response was attributed to the additional modulation of the sensor resistance due to potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire. Also nanobridge structure enabled fast recovery behavior because desorbed gas molecules can be easily swept away from the surface of ZnO nanowire without re-adsorption.

L-Cysteine-capped ZnS quantum dots based fluorescence sensor for Cu2+ ion

Abstract: This paper describes the investigation of surface modified quantum dots (QDs) as a sensing receptor for Cu 2+ ion detection by optical approach. Water-soluble l -cysteine-capped ZnS QDs have been synthesised in aqueous medium. These functionalised nanoparticles were used as a fluorescence sensor for Cu (II) ion, involved in the fluorescence quenching. The optimum fluorescence intensity was found to be at pH 5.0 with a nanoparticle concentration of 2.5 mg L −1 . The effect of foreign ions on the intensity of ZnS QDs showed a low interference response towards other metal ions except Ag + and Fe 3+ ions. The quenching mechanism was studied and the results show the existence of both static and dynamic quenching processes. However, static quenching is more prominent of the two. The limit of detection of this system was found to be 7.1 × 10 −6 M. When compared with single organic fluorophores, l -cysteine-capped ZnS QDs are brighter and more stable against photobleaching. This method is not only simple, sensitive and low cost, but also reliable for practical applications.

Polyaniline/silver nanocomposites: Dielectric properties and ethanol vapour sensitivity

Abstract: Polyaniline/silver (PANI/Ag) nanocomposites were prepared by in-situ oxidative polymerization of ani-line monomer in the presence of different concentrations of Ag nanoparticles. The formation of PANI/Agnanocomposite was characterized by UV–vis spectroscopy, energy dispersion X-ray (EDX) and transmis-sion electron microscopy (TEM). TEM images showed that the particle size increased with increasing Agconcentrationinthecomposite,owingtotheaggregationeffect.TheACconductivityanddielectricprop-erties of pure PANI and PANI/Ag nanocomposites were measured in the frequency range of 10 3 –10 6 Hz.Higherconductivity,dielectricconstantanddielectriclossofPANI/AgnanocompositesthanthoseofpurePANIwereobserved.TheconductivityofthenanocompositesincreasedwithincreasingAgconcentration.The gas-responses of the PANI/Ag nanocomposite towards low concentrations of ethanol was examinedand compared with that of the pure PANI. The nanocomposite was found to possess superior ethanolsensing capacity compared to pure PANI and it showed linear relationship between the responses andthe ethanol and/or Ag concentration. The Fourier transform infrared (FT-IR) spectroscopy was used toexplain the sensing mechanism.© 2009 Elsevier B.V. All rights reserved.

Carbon nanotubes based transistors as gas sensors: State of the art and critical review

Abstract: In this paper we present recent studies concerning gas sensors based on carbon nanotube field effect transistors (CNTFETs). Although these devices have allowed one to realize sensors with an impressive sensitivity compared to existing technologies, the physical interpretation of the interaction between the gas molecules and the CNTFETs has not been clarified yet. In this contribution, we try to find some consistency between the physical interpretations advanced by the different scientific teams working on the subject and to answer some unsolved questions. Moreover, considering that the selectivity is the main issue, we analyze the different routes that have been proposed to overcome this problem: functionalization using polymers, diversification of the source/drain metal electrodes, metal decoration of SWCNT mats, exploitation of the desorption time of the different gases. For each technique we try to evaluate the advantages and the drawbacks.

Gas sensing characteristics and porosity control of nanostructured films composed of TiO2 nanotubes

Abstract: Preparation and morphology control of TiO 2 nanostructured films for gas sensor applications were investigated. To examine the effect of the morphology of sensing films on the sensing characteristics, TiO 2 with different morphologies, nanoparticles and nanotubes, were used for the film preparation. TiO 2 nanotubes were prepared by a hydrothermal treatment of TiO 2 nanoparticles in a NaOH solution at 160, 200, and 230 °C for 24 h and subsequent washing with an HCl solution. Uniform sized TiO 2 nanotubes of 1 μm in length and 50 nm in diameter were formed at 230 °C. The sensing films composed of nanotubes prepared at 230 °C showed a high sensor response to toluene at 500 °C as compared with those composed of TiO 2 nanoparticles. Scanning electron microscope (SEM) analysis and pore size distribution measurements indicated that the sensing films composed of the TiO 2 nanotubes had a high porous morphology with a peak pore size of around 200 nm, which can promote the diffusion of toluene deep inside the films and improve the sensor response. The obtained results demonstrated the importance of microstructure control of sensing layers for improving the sensitivity to large size molecules like volatile organic compounds (VOCs).

Gold nanowire array electrode for non-enzymatic voltammetric and amperometric glucose detection

Abstract: The non-enzymatic voltammetric and amperometric detection of glucose using a gold nanowire array electrode is described. The voltammetric detection of glucose was performed by cyclic and differential-pulse voltammetry. The detection of glucose by partial and direct oxidation of glucose during the anodic and cathodic potential sweeps was shown in cyclic voltammetry. An unusual decrease in overpotential for partial oxidation of glucose on a Au NW array electrode was observed. A linear differential-pulse voltammetric response for partial oxidation of glucose was observed up to a glucose concentration of at least 20 mM with a sensitivity of 41.9 μA mM−1 cm−2 and detection limit below 30 μM (signal-to-noise ratio of 3) for glucose oxidation at low potentials, where the influence of possible intermediates can be avoided. The amperometric response was also linear up to a glucose concentration of 10 mM with a sensitivity of 309.0 μA mM−1 cm−2. The wide dynamic range and high sensitivity, selectivity and stability, as well as good biocompatibility of the Au NW electrode make it promising for the fabrication of non-enzymatic glucose sensors.

Studies on tin oxide-intercalated polyaniline nanocomposite for ammonia gas sensing applications

Abstract: Thin films of tin oxide-intercalated polyaniline nanocomposite have been deposited at room temperature, through solution route technique. The as-grown films were studied for some of the useful physicochemical properties, making use of XRD, FTIR, SEM, etc. and optical methods. XRD studies showed peak broadening and the peak positions shift from standard values, indicating presence of tin oxide in nanoparticles form in the polyaniline (PANI) matrix. FTIR study shows presence of the Sn–O–Sn vibrational peak and characteristic vibrational peaks of PANI. Study of SEM micrograph revealed that the composite particles have irregular shape and size with micellar templates of PANI around them. AFM images show topographical features of the nanocomposite similar to SEM images but at higher resolution. Optical absorbance studies show shifting of the characteristics peaks for PANI, which may be due to presence of tin oxide in PANI matrix. On exposure to ammonia gas (100–500 ppm in air) at room temperature, it was found that the PANI film resistance increases, while that of the nanocomposite (PANI + SnO2) film decreases from the respective unexposed value. These changes on removal of ammonia gas are reversible in nature, and the composite films showed good sensitivity with relatively faster response/recovery time. © 2009 Elsevier B.V. All rights reserved.

Bio-sensing textile based patch with integrated optical detection system for sweat monitoring

Abstract: Sensors, which can be integrated into clothing and used to measure biochemical changes in body fluids, such as sweat, constitute a major advancement in the area of wearable sensors. Initial applications for such technology exist in personal health and sports performance monitoring. However, sample collection is a complicated matter as analysis must be done in real-time in order to obtain a useful examination of its composition. This work outlines the development of a textile-based fluid handling platform which uses a passive pump to gather sweat and move it through a pre-defined channel for analysis. The system is tested both in vitro and in vivo. In addition, a pH sensor, which depends on the use of a pH sensitive dye and paired emitter-detector LEDs to measure colour changes, has been developed. In vitro and on-body trials have shown that the sensor has the potential to record real-time variations in sweat during exercise.

Electrochemical glucose sensor based on one-step construction of gold nanoparticle-chitosan composite film

Abstract: A simple and controllable electrodeposition method for the preparation of a chitosan–gold nanoparticles (GNPs) nanocomposite sensing film on a glassy carbon electrode (GCE) surface was proposed and further used for the construction of an glucose non-enzymatic sensor. This novel interface embedded in situ GNPs in chitosan hydrogel was constructed by one-step electrochemical deposition in solution containing tetrachloroauric (III) acid (HAuCl4) and chitosan. This deposited interface possessed excellent stability by the characterization of cyclic voltammetry and pulse voltammetry in phosphate buffer (pH 7.10). The application in serum analysis as a possible alternative for electrochemical detection of glucose has been investigated. Several key operational parameters affecting the electrochemical response of nanostructured sensing film were examined and optimized, such as deposition conditions, scan rate, electrolyte and its pH values. As the nanostructured sensing film provides plenty of active sites for the direct oxidation of glucose, the glucose sensor exhibited excellent performance including wide linearity, simple operation and good stability at the optimized conditions. The glucose sensor exhibited good linear behavior in the concentration range from 4.00 × 10 −4

An amperometric glucose biosensor fabricated with Pt nanoparticle-decorated carbon nanotubes/TiO2 nanotube arrays composite

Abstract: Carbon nanotubes (CNTs)-modified titania nanotube (NT) arrays are prepared by vapor-growing CNTs in the inner of titania NTs. Pt nanoparticles of ∼3 nm in diameter are uniformly decorated on the as synthesized titania-supported CNTs (TiO2/CNTs) electrode, showing remarkably improved catalytic activities for the oxidation of hydrogen peroxide. The consequent glucose biosensor fabricated by modifying TiO2/CNT/Pt electrode with glucose oxidase (GOx) presents a high sensitivity of 0.24 μA mM−1 cm−2 to glucose in the range of 0.006 mM to 1.5 mM with a response time of less than 3 s and a detection limit of 5.7 μM at 3 signal/noise ratio.

Real-time monitoring of sub-ppb concentrations of aromatic volatiles with a MEMS-enabled miniaturized gas-chromatograph

Abstract: Micromachined gas-chromatographic (GC) components in combination with high sensitivity MOX detectors and novel pre-concentration materials were utilized to develop a miniaturized, portable, stand-alone sub-ppb level monitoring system for aromatic volatile organic compounds (VOC). Using metal oxide semiconductor (MOX) gas sensors as detectors in a GC system, the intrinsic analytic selectivity of GC is exploited in a simplified architecture with on-board generated carrier gas. The work reported here includes the study of innovative pre-concentration materials, the micromachining of GC components and devices, the fabrication and characterization of complete system prototypes, and the development of application-specific control electronics. The results of both laboratory trials and successful real-world cross-validation with a reference analyzer are described.

Iron oxide-chitosan nanobiocomposite for urea sensor

Abstract: Urease (Ur) and glutamate dehydrogenase (GLDH) have been co-immobilized onto superparamegnatic iron oxide (Fe3O4) nanoparticles-chitosan (CH) based nanobiocomposite film deposited onto indium-tin-oxide (ITO) coated glass plate via physical adsorption for urea detection. The magnitude of magnetization (60.9 emu/g) of Fe3O4 nanoparticles (∼22 nm) estimated using vibrating sample magnetometer (VSM) indicates superparamagnetic behaviour. It is shown that presence of Fe3O4 nanoparticles results in increased active surface area of CH-Fe3O4 nanobiocomposite for immobilization of enzymes (Ur and GLDH), enhanced electron transfer and increased shelf-life of nanobiocomposite electrode. Differential pulse voltammetry (DPV) studies show that Ur-GLDH/CH-Fe3O4/ITO bioelectrode is found to be sensitive in the 5–100 mg/dL urea concentration range and can detect as low as 0.5 mg/dL. A relatively low value of Michaelis–Menten constant (Km, 0.56 mM) indicates high affinity of enzymes (Ur and GLDH) for urea detection.

Equivalence between thermal and room temperature UV light-modulated responses of gas sensors based on individual SnO2 nanowires

Abstract: We demonstrate that illuminating metal oxide gas sensors with ultra-violet light is a viable alternative not only to activate but also to modulate their response towards oxidizing gases. Here, the performance of individual monocrystalline SnO 2 nanowires to NO 2 at room temperature as function of the flux and the energy of photons is studied. The results reveal that nearly identical responses, similar to thermally activated sensor surfaces, can be achieved by choosing the optimal illumination conditions. On the basis these results, a qualitative model to explain the response of these sensors towards oxidizing gases is proposed. This finding paves the way to the development of conductometric gas sensors operating at room temperature.

A single ZnO tetrapod-based sensor

Abstract: Transferable ZnO tetrapods were grown by an aqueous solution method. An individual ZnO tetrapod-based sensor was fabricated by in situ lift-out technique and its ultraviolet (UV) and gas sensing properties were investigated. This single tetrapod-based device responds to the UV light rapidly and showed a recovery time of about 23 s. The sensitivity of a single ZnO tetrapod sensor to oxygen concentration was also investigated. We found that when UV illumination is switched off, the oxygen chemisorption process will dominate and assists photoconductivity relaxation. Thus relaxation dynamics is strongly affected by the ambient O 2 partial pressure as described. We also studied the response of ZnO tetrapod-based sensor in various gas environments, such as 100 ppm H 2 , CO, i -butane, CH 4 , CO 2 , and SO 2 at room temperature. It is noted that ZnO tetrapod sensor is much more sensitive to H 2 , i -butane and CO. It is demonstrated that a ZnO tetrapod exposed to both UV light and hydrogen can provide a unique integrated multiterminal architecture for novel electronic device configurations.

One-step synthesis of silver nanoparticles/carbon nanotubes/chitosan film and its application in glucose biosensor

Abstract: One-step synthesis of silver nanoparticles/carbon nanotubes/chitosan film (Ag/CNT/Ch) was firstly proposed as a novel immobilization matrix for the enzymes to fabricate sensitive glucose biosensor. The biosensor was prepared by embedding horseradish peroxidase (HRP) and glucose oxidase (GOD) in Ag/CNT/Ch hybrid films based on layer by layer technique. The electron mediator, o-phenylenediamine (OPD), was also co-immobilized with HRP in the inner layer on the surface of an indium tin oxide (ITO) electrode. Hydrogen peroxide produced by the GOD catalytic oxidation of glucose was then detected by OPD in the presence of HRP. Under the optimized experimental conditions, the resulting biosensor could detect glucose in a linear range from 0.5 to 50 μM with a detection limit of 0.1 μM at a signal-to-noise ratio of 3. The sensitivity was calculated as 135.9 μA mM−1. The proposed biosensor offered sensitive amperometric responses to glucose based on the Ag/CNT/Ch films.

Microstructure and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires

Abstract: Tin oxide (SnO2) nanowires with a tetragonal structure were synthesized by thermal evaporation of tin grains at 900 °C. The obtained nanowires were doped with palladium. The morphology, crystal structure, and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires were investigated. SnO2 nanowires were approximately 30–200 nm in diameter and several tens of micrometers in length. Gas sensors based on undoped, 0.8 wt% Pd-doped, and 2 wt% Pd-doped SnO2 nanowires were fabricated. These SnO2 nanowire gas sensors showed a reversible response to H2 gas at an operating temperature of RT—300 °C. The sensor response increased with increasing Pd concentration. The 2 wt% Pd-doped SnO2 nanowire sensor showed a response as high as 253 for 1000 ppm H2 gas at 100 °C. The results demonstrated that Pd doping improved the sensor response and lowered the operating temperature at which the sensor response was maximized.

Growth and selective acetone detection based on ZnO nanorod arrays

Abstract: High preferential c -axis oriented ZnO nanorods aligned on SiO 2 /Si substrates with interdigital electrodes have been successfully fabricated through aqueous solution methods. The transparent ZnO buffer layer covered on both the conducting electrodes and the insulating SiO 2 spacer regions acts as lattice-matched template for the assembly of c -axis oriented ZnO nanorod arrays, and the subsequent growth of ZnO nanorods has been completed via a low temperature hydrothermal process. Detailed structural characterizations reveal that the as-synthesized nanorods are single crystalline, with a hexagonal phase, and with growth along the [0 0 1] direction. The gas-sensing properties of ZnO nanorod thin films are studied. It is found that the ZnO nanorod thin film sensor exhibits excellent sensing properties towards acetone at 300 °C with the response time shorter than 5 s.

Solvothermal synthesis and gas-sensing performance of Co3O4 hollow nanospheres

Abstract: Co 3 O 4 hollow nanospheres with a diameter of 200–300 nm were synthesized by a surfactant-assisted solvothermal method. X-ray diffraction and Raman spectrum measurements demonstrate that the products are pure face-centered cubic Co 3 O 4 . Transmission electron microscopy and selected area electron diffraction analyses reveal that the walls of Co 3 O 4 hollow nanospheres have a uniform thickness of ∼40 nm and are constructed by an oriented aggregation of Co 3 O 4 nanocrystals. The optical absorption properties of the Co 3 O 4 hollow nanospheres were investigated by UV–vis spectroscopy and the results indicate that the Co 3 O 4 hollow nanospheres are semiconducting with direct band gaps of 2.23, 1.25 and 1.00 eV. The gas-sensing performance of the as-prepared Co 3 O 4 hollow nanospheres was investigated towards a series of typical organic solvents and fuels. The Co 3 O 4 hollow nanospheres show good sensing performances towards toluene and acetone vapors with rapid response and high sensitivity at low operating temperature.

ZnO hollow spheres: Preparation, characterization, and gas sensing properties

Abstract: ZnO hollow spheres were successfully prepared by using carbon microspheres as templates and characterized by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). A gas sensor was fabricated from the as-prepared ZnO hollow spheres and tested to different concentrations of NH3 and NO2 at different operating temperatures. The results showed that the ZnO hollow-sphere sensor exhibited extremely different sensing behaviors to NH3 and NO2. The optimum operating temperature of the sensor was 220 °C for NH3 and 240 °C for NO2, respectively. At 220 °C, the responses to 25, 50 and 75 ppm NH3 were 7.9, 11.1 and 20.4 and the response times were as long as several minutes. At 240 °C, the responses to 10, 50 and 100 ppm NO2 were 140.6, 172.8 and 286.8 and the corresponding response times were 31, 19 and 9 s. In addition, it is also shown that the gas sensor exhibited much higher response to NO2 than to other gases at 240 °C, implying the good selectivity and potential application of the sensor for detecting NO2.

A sensitive and selective sensor for dopamine determination based on a molecularly imprinted electropolymer of o-aminophenol

Abstract: A simple and reliable method was proposed for preparing a selective dopamine (DA) sensor based on a molecularly imprinted electropolymer of o-aminophenol. The sensor is selective for the determination of DA in the presence of high concentrations of ascorbic acid (AA), with a maximum molar ratio of 1/1000. The molecular imprinted (MIP) sensor was tested by cyclic voltammetry (CV) as well as differential pulse voltammetry (DPV) to verify the changes in oxidative currents of ferricyanide. In optimized conditions, DA at concentrations of 2 × 10−8 to 0.25 × 10−6 mol/L could be determined with a detection limit of 1.98 × 10−9 mol/L (S/N = 3). The MIP sensor showed high selectivity, sensitivity, and reproducibility. Determination of DA in simulated samples of dopamine hydrochloride showed good recovery.

Enhanced H2S sensing characteristics of SnO2 nanowires functionalized with CuO

Abstract: The CuO-functionalized SnO 2 nanowire (NW) sensors were fabricated by depositing a slurry containing SnO 2 NWs on a polydimethylsiloxane (PDMS)-guided substrate and subsequently dropping Cu nitrate aqueous solution. The CuO coating increased the gas responses to 20 ppm H 2 S up to ∼74-fold. The R a / R g value of the CuO-doped SnO 2 NWs to 20 ppm H 2 S was as high as 809 at 300 °C, while the cross-gas responses to 5 ppm NO 2 , 100 ppm CO, 200 ppm C 2 H 5 OH, and 100 ppm C 3 H 8 were negligibly low (1.5–4.0). Moreover, the 90% response times to H 2 S were as short as 1–2 s at 300–400 °C. The selective detection of H 2 S and enhancement of the gas response were attributed to the uniform distribution of the sensitizer (CuO) on the surface of the less agglomerated network of the SnO 2 NWs.

High-performance NO2 gas sensor based on ZnO nanorod grown by ultrasonic irradiation

Abstract: A facile and fast sonochemical route for the fabrication of a resistive-type ZnO gas sensor has been demonstrated. Vertically aligned ZnO nanorod arrays were grown on a Pt-electrode patterned alumina substrate under ambient conditions. The average diameter and length of the ZnO nanorods were 50 and 500 nm, respectively. Sonochemically grown ZnO nanorod gas sensor was highly sensitive to NO2 gas with a very low detection limit of 10 ppb at 250 °C; further, its response and recovery time were short. Considering the advantageous properties of this sonochemical technique, we believe that it can be used to fabricate high-performance gas sensors.

Characterisation of commercially available electrochemical sensing platforms

Abstract: Disposable screen-printed electrodes are routinely used for sensitive electro-analytical sensing but their reactivity and performance can greatly vary In this paper we have electrochemically interrogated and characterised a range of commercially available screen-printed electrodes from Zensor, Dropsens and Kanichi with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) Differing electrochemical reactivities are observed with the optimal electrochemical performance observed for Dropsens and certain Kanichi electrochemical platforms with the greatest reproducibility (relative standard deviation, %RSD) observed with the electrodes from Kanichi The effect of temperature and potential cycling the screen-printed electrochemical platforms is also explored This report allows researchers to make informed decisions in sensor selection, design and development © 2009 Elsevier BV All rights reserved

CO, NO2 and NOx urban pollution monitoring with on-field calibrated electronic nose by automatic bayesian regularization

Abstract: Low cost gas multisensor devices can represent an efficient solution for densifying the sparse urban air pollution monitoring mesh. In a previous work, we proposed and evaluated the calibration of such a device using short term on-field recorded data for the benzene pollution quantification. In this work, we present and discuss the results obtained for CO, NO2 and total NOx pollutants concentration estimation with the same set up. Conventional air pollution monitoring station is used to provide reference data. We show how a multivariate calibration can be achieved with the use of two weeks long on-field data recording and neural regression systems. Also for these pollutants, no significant performance boost was detectable when longer recordings were used. The influence of an appropriate feature selection for achieving optimal performances is also discussed comparing long term performance results of the obtained calibrations. Benefits and issues of multivariate correlation based calibration are evaluated during one year long measurement campaign.