A gas-sensitive hybrid material consisting of Cu2O nanoparticle-decorated WO3 nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. ...Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO3 nanoneedles decorated with p-type Cu2O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO3 nanoneedles) and a low detection limit (below 300 ppb of H2S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p–n heterojunctions created at the nanoscale in our hybrid nanomaterial.
We report for the first time the successful synthesis of palladium (Pd) nanoparticle (NP)-decorated tungsten trioxide (WO3) nanoneedles (NNs) via a two-step aerosol-assisted chemical vapor deposition ...approach. Morphological, structural, and elemental composition analysis revealed that a Pd(acac)2 precursor was very suitable to decorate WO3 NNs with uniform and well-dispersed PdO NPs. Gas-sensing results revealed that decoration with PdO NPs led to an ultrasensitive and selective hydrogen (H2) gas sensor (sensor response peaks at 1670 at 500 ppm of H2) with low operating temperature (150 °C). The response of decorated NNs is 755 times higher than that of bare WO3 NNs. Additionally, at a temperature near that of the ambient temperature (50 °C), the response of this sensor toward the same concentration of H2 was 23, which is higher than that of some promising sensors reported in the literature. Finally, humidity measurements showed that PdO/WO3 sensors displayed low-cross-sensitivity toward water vapor, compared to bare WO3 sensors. The addition of PdO NPs helps to minimize the effect of ambient humidity on the sensor response.
Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto ...micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C2H5OH, H2, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H2, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment.
Tungsten oxide nanoneedles functionalized with gold or platinum nanoparticles (NPs) are synthesized using a single‐step aerosol‐assisted chemical vapor deposition method. They are integrated into gas‐sensor platforms, which are used to discriminate analytes present in proton‐exchange fuel cells. This co‐deposition method is demonstrated to be effective both for incorporating metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides, and for directly integrating these materials with devices.
Tin oxide nanorods (NRs) are vapour synthesised at relatively lower temperatures than previously reported and without the need for substrate pre-treatment, via a vapour-solid mechanism enabled using ...an aerosol-assisted chemical vapour deposition method. Results demonstrate that the growth of SnO2 NRs is promoted by a compression of the nucleation rate parallel to the substrate and a decrease of the energy barrier for growth perpendicular to the substrate, which are controlled via the deposition conditions. This method provides both single-step formation of the SnO2 NRs and their integration with silicon micromachined platforms, but also allows for in-situ functionalization of the NRs with gold nanoparticles via co-deposition with a gold precursor. The functional properties are demonstrated for gas sensing, with microsensors using functionalised NRs demonstrating enhanced sensing properties towards H2 compared to those based on non-functionalised NRs.
•The influence of the testing chamber design on a gas sensor response.•Modeling and simulation of the gas transport mechanism inside a testing chamber for gas characterization.•Modeling of a gas flow ...by a finite volume method solving the 3D unsteady Navier-Stokes equations.•High sensitive SnO2 ethanol sensor.
Gas concentration measurements by means of metal oxide microsensors represent a promising issue due to several advantages (size, low cost, power consumption, reliability…). However, improvements are required to increase performances of complete experimental systems including microsensor and testing chamber at least. This paper deals with the study of different size and shape configurations of gas testing chamber, by coupling 3D unsteady modelling and experiments in the case of a SnO2 sensor with ethanol gas flow. The influence of the testing-chamber design on the gas flow hydrodynamics and on the system response is shown. A new 3D-printed prototype chamber (boat-shape design), as compared to the commonly used testing chamber (cross-shape design), leads to an increase of the dynamics, an enhancement of the gas concentration homogeneity and a significant reduction of flow recirculation and dead volumes. In this work we have shown that the optimization of the test chamber (volume and shape) makes it possible to get as close as possible to the real electrical characteristics of the sensor. Consequently thanks to these new achieved characteristics, the performances of the whole system are improved.
•A new architecture has been proposed for planar heated resistive gas sensors.•It uses one of the sensing electrodes simultaneously as heating element.•It consumes less metallic ink and substrate ...area than a usual planar configuration.•Thus, it enhances power consumption and thermal homogeneity.•It avoids printing robust interdielectric layer as in stack configurations.
This paper presents a new coplanar architecture to implement the electrodes and the heating element of printed gas sensors. The design includes two electrodes and three contacts. One of the electrodes works as heating element and, simultaneously, drains the sensing current. The electrical modelling of the transducers and its electronic implementation are reported. As this new approach is related to the electrical topology of the system, a reduction in the number of conductive elements will be obtained for any geometry, deposition method, and gas sensing layer. Compared with other coplanar topologies, this approach simplifies the transducers processing to a single printing step, avoiding the use of an inter-dielectric layer between heater and electrodes, and reducing the amount of electrically conductive ink necessary to pattern heater and electrodes of the transducers. This cost-effective architecture and process was applied to the fabrication of heated transducers for metal-oxide gas sensors. The two electrodes were made by inkjet printing of gold on polyimide foil. For the validation of the concept, a Pt loaded WO3 sensing layer was grown on top of these transducers printed with the proposed topology. When tested against H2, diluted in air, their response was as good as the one obtained employing the classical topology. This simple architecture has strong potential for the realization of fully printed resistive gas sensors and can be implemented as well in clean room processed transducers.
The synthesis of functional low-dimensional metal oxides for gas sensing has been attracting widespread research interest in the last few years. Here we review the results obtained employing the ...aerosol assisted chemical vapour deposition method, which is a flexible, inexpensive and high-yield technique for growing both polycrystalline or single-crystalline metal oxides with remarkable gas sensing properties. We show how this technique is suitable for growing metal-decorated low-dimensional nanostructures directly on alumina or silicon-based transducers, which helps in bridging the gap currently existing between nanotechnology-based gas sensors and mass-market applications.
•The aerosol assisted chemical vapour deposition (AA-CVD) of thin films is reviewed.•This method allows for growing metal-decorated low-dimensional metal oxides.•The bottom-up integration of nanostructured metal oxides in devices is discussed.•The gas sensing properties of AA-CVD grown metal oxides are reviewed.
Mass spectrometry-based metabolomics provides a new approach to interrogate mechanistic biochemistry related to natural processes such as health and disease. Physiological and pathological ...conditions, however, are characterized not only by the identities and concentrations of metabolites present, but also by the location of metabolites within a tissue. Unfortunately, most relevant MS platforms in metabolomics can only measure samples in solution, therefore metabolites are typically extracted by tissue homogenization. Recent developments of imaging-MS technologies, however, have allowed particular metabolites to be spatially localized within biological tissues. In this context, Nanostructure-Initiator Mass Spectrometry (NIMS), a matrix-free technique for surface-based analysis, has proven an alternative approach for tissue imaging of metabolites. Here we review the basic principles of NIMS for tissue imaging and show applications that can complement LC/MS and GC/MS-based metabolomic studies investigating the mechanisms of fundamental biological processes. In addition, the new surface modifications and nanostructured materials herein presented demonstrate the versatility of NIMS surface to expand the range of detectable metabolites.
This article is part of a Special Issue entitled: Imaging Mass Spectrometry: A User’s Guide to a New Technique for Biological and Biomedical Research.
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► NIMS has proven an alternative matrix-free approach for tissue imaging of metabolites. ► We review the basic principles of NIMS for tissue imaging. ► We show applications that can complement LC/MS and GC/MS-based metabolomic studies. ► We present alternative NIMS surfaces to expand the range of detectable metabolites.
In this paper, we report the fabrication and characterization of a portable transdermal alcohol sensing device via a human finger, using tin dioxide (SnO2) chemoresistive gas sensors. Compared to ...conventional detectors, this non-invasive technique allowed us the continuous monitoring of alcohol with low cost and simple fabrication process. The sensing layers used in this work were fabricated by using the reactive radio frequency (RF) magnetron sputtering technique. Their structure and morphology were investigated by means of X-ray spectroscopy (XRD) and scanning electron microscopy (SEM), respectively. The results indicated that the annealing time has an important impact on the sensor sensitivity. Before performing the transdermal measurements, the sensors were exposed to a wide range of ethanol concentrations and the results displayed good responses with high sensitivity, stability, and a rapid detection time. Moreover, against high relative humidity (50% and 70%), the sensors remained resistant by showing a slight change in their gas sensing performances. A volunteer (an adult researcher from our volunteer group) drank 50 mL of tequila in order to realize the transdermal alcohol monitoring. Fifteen minutes later, the volunteer’s skin started to evacuate alcohol and the sensor resistance began to decline. Simultaneously, breath alcohol measurements were attained using a DRAGER 6820 certified breathalyzer. The results demonstrated a clear correlation between the alcohol concentration in the blood, breath, and via perspiration, which validated the embedded transdermal alcohol device reported in this work.
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