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Detection and Discrimination of Volatile Organic Compounds Using a Single Multi-resonance Mode Piezotransduced Silicon Bulk Acoustic Wave Resonator (PSBAR) as Virtual Sensor Array

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Abstract

This paper describes the detection of volatile organic compounds (VOCs) using an e-nose system based on a virtual sensor array (VSA). The VSA was realized by seven different resonant modes of a single piezotransduced silicon bulk acoustic wave resonator (PSBAR) which can greatly reduce the complexity of a conventional e-nose system. The PSBAR was designed and fabricated using standard CMOS compatible process. The resonant modes of the PSBAR and its capability of VOCs discrimination were theoretically explored through finite element analysis. The discrimination effect was enhanced by the non-uniform adsorption of gas molecules on the top, side and bottom regions of the resonator. Score plots and radar fingerprints obtained respectively from principal component analysis (PCA) and fitted coefficient of adsorption isotherms for each VOC compose sufficient information to successfully discriminate different VOCs. The proposed novel VSA shows great potential as a compact and promising e-nose system.

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... VOCs can have short and/or long-term negative effects on human health and life worldwide. 4 VOCs can be emitted from household products such as paints, paint strippers, wood preservatives, wax, pesticides, aerosol sprays, carpets, and many cleaning, disinfecting, cosmetic and degreasing products. Many pollutants are emitted into the environment as a result of industry, traffic, heating, etc. Aromatic and aliphatic hydrocarbons constitute a significant portion of these pollutants. ...
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... The film thickness and refractive index of C1 LB thin films were determined by fitting the experimental SPR curves using Winspall software (by the Wolfgang Knoll group).60 Film thickness and refractive index values(4,8,12,16 and 20 layers) are given inTable 1. The thickness and refractive index of the C1 LB thin film show an increase depending on the number of layers. ...
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An electrodeless monolithic multichannel quartz crystal microbalance (MQCM) sensor was developed via the direct growth of ZnO nanorod patterns of various sizes onto an electrodeless quartz crystal plate. The patterned ZnO nanorods acted as independent resonators with different frequencies upon exposure to an electric field. The added mass of ZnO nanostructures was found to significantly enhance the quality factor (QF) of the resonator in electrodeless QCM configuration. The QF increased with the length of the ZnO nanorods; ZnO nanorods 5 m in length yielded a 7-fold higher QF compared to the QF of a quartz plate without ZnO nanorods. In addition, the ZnO nanorods offered enhanced sensitivity due to the enlarged sensing area. The developed sensor was used as an electronic nose for detection of vapor mixtures with impurities.
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An array of quartz crystals coated with different room-temperature ionic liquids (RTILs) is proposed for the analysis of flavors by quartz crystal microbalance (QCM) measurements. Seven RTILs were adopted as sensing layers, all containing imidazolium or phosphonium cations, differing from one another in the length and branching of alkyl groups, and neutralized by different anions. The array was at first applied to the analysis of 31 volatile organic compounds (VOCs) such as alcohols, phenols, aldehydes, esters, ketones, acids, amines, hydrocarbons and terpenes, chosen as representative components of a wide variety of food flavors. Multivariate data analysis by the principal component analysis (PCA) approach of the set of the corresponding responses led to separated clusters for these different chemical categories. To prove further the good performance of the RTIL coated quartz crystal array as "electronic nose", it was applied to the analysis of headspaces from cinnamon samples belonging to different botanical varieties (cinnamon zeylanicum and cinnamon cassia). PCA applied to responses recorded on different stocks of samples of both varieties showed that they could be fully discriminated.
Article
A surface acoustic wave (SAW) sensor array has been developed in order to discriminate Spanish wine coming from different grape varieties and elaboration processes. Sensors were coated with diverse thicknesses of polyepichlorohydrin (PECH), polyetherurethane (PEUT) and polydimethylsiloxane (PDMS). Linear techniques as principal component analysis (PCA) and linear discriminant analysis (LDA) and non-linear ones as probabilistic neural networks (PNN) have been used for pattern recognition. A classification success rate of 86% has been achieved.
Article
The gas sensing properties of graphene-like nano-sheets deposited on 36° YX lithium tantalate (LiTaO3) surface acoustic wave (SAW) transducers are reported. The thin graphene-like nano-sheets were produced via the reduction of graphite oxide which was deposited on SAW interdigitated transducers (IDTs). Their sensing performance was assessed towards hydrogen (H2) and carbon monoxide (CO) in a synthetic air carrier gas at room temperature (25°C) and 40°C. Raman and X-ray photoelectron spectroscopy (XPS) revealed that the deposited graphite oxide (GO) was not completely reduced creating small, graphitic nanocrystals ∼2.7nm in size.
Article
1 I. 1 II. 7 III. 8 IV. 10 V. 12 13 References 13 SUMMARY: Plants synthesize an amazing diversity of volatile organic compounds (VOCs) that facilitate interactions with their environment, from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites and herbivores. Recent progress in -omics technologies resulted in the isolation of genes encoding enzymes responsible for the biosynthesis of many volatiles and contributed to our understanding of regulatory mechanisms involved in VOC formation. In this review, we largely focus on the biosynthesis and regulation of plant volatiles, the involvement of floral volatiles in plant reproduction as well as their contribution to plant biodiversity and applications in agriculture via crop-pollinator interactions. In addition, metabolic engineering approaches for both the improvement of plant defense and pollinator attraction are discussed in light of methodological constraints and ecological complications that limit the transition of crops with modified volatile profiles from research laboratories to real-world implementation.
Article
Tropical Morpho butterflies are famous for their brilliant iridescent colours, which arise from ordered arrays of scales on their wings. Here we show that the iridescent scales of the Morpho sulkowskyi butterfly give a different optical response to different individual vapours, and that this optical response dramatically outperforms that of existing nano-engineered photonic sensors. The reflectance spectra of the scales provide information about the nature and concentration of the vapours, allowing us to identify a range of closely related vapours–water, methanol, ethanol and isomers of dichloroethylene when they are analysed individually. By comparing the reflectance as a function of time for different vapours, we deduce that wing regions with scale structures of differing spatial periodicity give contributions to the overall spectral response at different wavelengths. Our optical model explains the effect of different components of the wing scales on the vapour response, and could steer the design of new man-made optical gas sensors.
Article
The adsorption of volatile organic compounds (VOC) onto soils plays an important role in the mobility of these kinds of contaminant through soils. It is therefore of interest to learn more about the mechanisms of interaction between VOC and soil particles. An experimental study has been carried out in order to determine the adsorption isotherms of volatile organic gases of different properties on soil minerals of different characteristics, working in a wide range of compound concentrations. The adsorption of seven organic compounds (n-hexane, n-heptane, n-octane, toluene, xylene, ethylbenzene, and methyl ethyl ketone) and of water vapor on sand, clay, and limestone has been analyzed. The influence of the presence of water on the adsorption of these compounds has also been analyzed, working at levels below the limit of applicability of Henry's law. The levels of relative air humidity used were 20 and 50%. The results show a big difference between the adsorption levels of the three soil minerals and a higher adsorption for polar compounds than for aliphatic and aromatic compounds. The water affects the VOC adsorption by decreasing the retention of these compounds to a greater extent for aromatic and aliphatic compounds than for the polar compound and by linearizing the isotherms. This reduction has been quantified by a simple exponential equation.
Article
Love-wave devices based on quartz piezoelectric substrate and SiO 2 guiding layer coated with a speci®c polysiloxane polymer are used to detect organophosphorus compounds. This allows to study af®nities of the polysiloxane polymer coating towards organophosphorus compounds, and to demonstrate the high sensitivity of love-wave devices for gas detection. We also present a theoretical model which describe wave propagation in love devices and allow to design optimized structures. Then, we discuss experimental results, in terms of interactions between sensor and vapor and in comparison to SAW results. # 2001 Elsevier Science B.V. All rights reserved.
Article
Carbon nanotube field-effect transistors (NTFETs) coated with poly(ethyleneimine) (PEI) and starch polymers exhibit electrical conductance changes upon exposure to CO2 gas in air at ambient temperature (see Figure). This observation has furnished nanoelectronic CO2 sensors. Their small size and low power consumption has enormous potential in wireless sensing for industrial and medical CO2 sensor units.
Article
Wird eine Fremdschicht auf eine zu Dickenscherungsschwingungen angeregte Schwingquarzplatte aufgebracht, so ndert sich die Eigenfrequenz der Platte infolge Vergrerung der schwingenden Masse. Da die Frequenznderung eines Schwingquarzes sehr genau vermessen werden kann, ergibt sich daraus eine sehr empfindliche Methode zur Wgung dnner Schichten.Massenbelegung der Fremdschicht und Frequenznderung sind einander proportional. Die Proportionalittskonstante lt sich aus der Eigenfrequenz des Schwingquarzes berechnen, so da eine empirische Eichung bei der Schichtwgung mit Schwingquarzen entfllt.Die Genauigkeit des Schichtwgeverfahrens ist in erster Linie durch die Temperaturabhngigkeit der Quarzeigenfrequenz begrenzt und betrgt bei 1 C zugelassener Temperaturschwankung etwa 4 10–9 g cm–2. Das entspricht einer mittleren Dicke von 0,4 bei der Dichte =1 g cm–3.Das Verfahren wurde auch zur direkten Wgung einer Masse ausgenutzt (Mikrowgung). Dabei lie sich eine Genauigkeit von 10–10g erreichen.
Article
Rapid aroma profiling of food products is a first step towards at-line flavor quality control and off-flavor assessment. In this paper, the potential of the zNose™ was tested for the first time to address this application. Honey was chosen as the food product because of its characteristic aroma. Both a chromatogram and a spectral approach to the interpretation of the zNose™ signal were established. In the chromatogram approach, the signal was treated as a traditional chromatogram and relative peak areas were calculated and compared, while the whole aroma spectrum was considered in the spectral approach. Shifts in GC-column retention times initially led to misinterpretation of the results in the spectral approach. A data processing algorithm was, hence, developed to correct for these shifts. Data were analyzed with principal component analysis (PCA), and canonical discriminant analysis (CDA). With both relative peak areas and corrected spectra, the aroma of six different honey varieties and two types of sugar solutions were successfully discriminated. A classification model was built and validated externally, which resulted in a correct classification of 15 out of 16 honey aroma profiles (94%).
Article
Flavour analysis is typically performed by human organoleptic analysis, which is often expensive and subjective. A novel approach using a surface acoustic wave sensing electronic nose (zNoseTM) for flavour analysis was explored to characterise 16 types of vegetable oils. Fatty acid composition, iodine value, peroxide value, p-anisidine value and free fatty acid analyses were conducted to determine the quality and characteristics of vegetable oils. The zNoseTM was employed successfully for qualitative distinction of flavour in different vegetable oils. This is achieved using a visual fragrance pattern, called a VaporPrintTM, derived from the frequency of the SAW detector. VaporPrintTM was shown to be particularly useful for assessing vegetable oil aroma profile in its entirety. This image is created by transforming the time variable to a radial angle with the beginning and end of the analysis occurring at 0°, or vertical. A Chemometric method, particularly principal component analysis (PCA), was conducted for electronic nose data processing and identification. Analysis of the score plot of the PCA for the zNoseTM measurement showed that 97% of the total variance in the data was described by PC 1 and PC 2. The loading plot revealed that five compounds (m,k,n,s, and p) were important for differentiate the vegetable oils.
Article
Surface acoustic wave (SAW) devices have been fabricated and tested as sensors of NH3 in gaseous phase. Polypyrrole films, prepared by Langmuir-Blodgett (LB) technique, have been deposited onto the surface of SAW devices as gas absorbent layers. Simultaneous measurements of SAW phase velocity and attenuation have been carried out in order to investigate the sensing mechanisms. The sensor response shows high sensitivity towards NH3 gas and excellent selectivity with respect to main interfering gases (CO, CH4, H2, O2), at room temperature. The low cross-sensitivity permits the recognition of NH3 gas as one component of a mixture of interfering gases.
Article
The mass sensitivity of an AlN thin film resonators operated in air at 6–8 GHz has been investigated in theory and experiment. The 30 × 30 μm wide resonators included a 180–300 nm thick, highly oriented AlN thin film, bottom and top electrode, and an acoustic reflector made of AlN/SiO2 multilayers. The top electrode was loaded by defined polymer layers to test sensitivity and simulation model. The impact of type and thickness of the top electrode was simulated. Ten to twenty nanometers thick PMMA coatings served to demonstrate sensitivity with a gettering gel in form of spontaneous adsorption of acetone from the vapour phase. Finally, a self-assembled monolayer of 11-mercaptoundecanoic acid was formed on a Pt top electrode for the demonstration of a sub-monolayer sensor in air. In both cases, pico-grams could be detected with a sensitivity up to 1000 m2/kg.
Article
By functionalizing the surfaces of ZnO nanobelts (NBs) with a thin self-assembled molecular layer, the electrical and optoelectronic performances of a single NB-based device are drastically improved. For a single NB-based device, due to energy band tuning and surface modification, the conductance was enhanced by 6 orders of magnitude upon functionalization; a coating molecule layer has changed a Schottky contact into an Ohmic contact without sophisticated deposition of multilayered metals. A functionalized NB showed negative differential resistance and exhibited huge improved photoconductivity and gas sensing response. The functionalized molecular layer also greatly reduced the etching rate of the ZnO NBs by buffer solution, largely extending their life time for biomedical applications. Our study demonstrates a new approach for improving the physical properties of oxide NBs and nanowires for device applications.
Article
This paper studies the application of lateral bulk acoustic thin-film piezoelectric-on-substrate (TPoS) resonators in high-frequency reference oscillators. Low-motional-impedance TPoS resonators are designed and fabricated in 2 classes--high-order and coupled-array. Devices of each class are used to assemble reference oscillators and the performance characteristics of the oscillators are measured and discussed. Since the motional impedance of these devices is small, the transimpedance amplifier (TIA) in the oscillator loop can be reduced to a single transistor and 3 resistors, a format that is very power-efficient. The lowest reported power consumption is approximately 350 microW for an oscillator operating at approximately 106 MHz. A passive temperature compensation method is also utilized by including the buried oxide layer of the silicon-on-insulator (SOI) substrate in the structural resonant body of the device, and a very small (-2.4 ppm/ degrees C) temperature coefficient of frequency is obtained for an 82-MHz oscillator.
Article
Olfaction exhibits both high sensitivity for odours and high discrimination between them. We suggest that to make fine discriminations between complex odorant mixtures containing varying ratios of odorants without the necessity for highly specialized peripheral receptors, the olfactory systems makes use of feature detection using broadly tuned receptor cells organized in a convergent neurone pathway. As a test of this hypothesis we have constructed an electronic nose using semiconductor transducers and incorporating design features suggested by our proposal. We report here that this device can reproducibly discriminate between a wide variety of odours, and its properties show that discrimination in an olfactory system could be achieved without the use of highly specific receptors.
Article
The sensing ability of individual SnO(2) nanowires and nanobelts configured as gas sensors was measured before and after functionalization with Pd catalyst particles. In situ deposition of Pd in the same reaction chamber in which the sensing measurements were carried out ensured that the observed modification in behavior was due to the Pd functionalization rather than the variation in properties from one nanowire to another. Changes in the conductance in the early stages of metal deposition (i.e., before metal percolation) indicated that the Pd nanoparticles on the nanowire surface created Schottky barrier-type junctions resulting in the formation of electron depletion regions within the nanowire, constricting the effective conduction channel and reducing the conductance. Pd-functionalized nanostructures exhibited a dramatic improvement in sensitivity toward oxygen and hydrogen due to the enhanced catalytic dissociation of the molecular adsorbate on the Pd nanoparticle surfaces and the subsequent diffusion of the resultant atomic species to the oxide surface.
Article
We observe second-harmonic generation from metamaterials composed of split-ring resonators excited at 1.5-micrometer wavelength. Much larger signals are detected when magnetic-dipole resonances are excited, as compared with purely electric-dipole resonances. The experiments are consistent with calculations based on the magnetic component of the Lorentz force exerted on metal electrons-an intrinsic second-harmonic generation mechanism that plays no role in natural materials. This unusual mechanism becomes relevant in our work as a result of the enhancement and the orientation of the local magnetic fields associated with the magnetic-dipole resonances of the split-ring resonators.
Article
The development of the electronic nose have paved the way for the classification of bacteria, to monitor air quality on the space shuttle, or to check the spoilage of foodstuff. However, the electronic nose still is unable to discriminated between flavors, perfumes, smells and as a replacement for the human nose. Although it has been used to detect some important nonodorant gases, it is not adapted to substances of daily importance in mammalian life such as the scent of other animals, foodstuff or spoilage. Due to such limitations, the electronic nose was developed to mimic the human nose. It turns out that the human nose's unequaled performance is not due to the high number of different human receptor cells, but their selectivity and their unsurpassed sensitivity for some analyte gases. As such, the success of the electronic nose will not rely on increasing the number of individual sensors and creating redundant information by adding more similar sensors, but rather on DNA, molecular, imprinted molecules or even mobilized natural receptors, which promise to increase the sensitivity and importantly selectivity. An increase in the sensitivity can be achieved by appropriate sample pretreatment and preconcentration techniques, whereas filters and separation units can be used to increase the selectivity and reduce interfering substances.