Acoustic Wave Chemical Sensors Research Articles

Detection of volatile organosulfur compounds by hydrogen-bond acidic polymer: A combined experimental and theoretical study

Volatile organic sulfur compounds (VOSCs) pose serious threats to environment and human health, while detection techniques of VOSCs are expensive and complex. Here, this paper first-time reported a hydrogen-bond acidic (HBA) polymer-based surface acoustic wave (SAW) chemical sensor for the detection of four VOSCs (methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and carbon disulfide). The results show that this sensor exhibited both excellent sensitivity (limit of detections ranging from 0.035 to 0.11 mg/m3) with fast response and recovery and high selectivity (2.23–49.6 times higher response than interference vapors) toward VOSCs at room temperature. The good performance is attributed to the hydrogen bonding between the sulfur atom of VOSCs and hydrogen atom of hexafluoroisopropanol (HFIP) groups in polymer chain. Fourier-transform infrared spectroscopy (FTIR) spectrum and first principle calculations were performed to further support this proposed mechanism.

표면음향파 화학센서를 이용한 수용액 중 시안화이온의 선택적인 고감도 검출

표면음향파 화학센서를 이용한 수용액 중 시안화이온의 선택적인 고감도 검출

Optimization of a BSP3-Coated Surface Acoustic Wave Chemical Sensor

The optimization of fluorinated bisphenol-containing polymer (BSP3)-coated surface acoustic wave (SAW) chemical sensor was performed for sensing organophosphorous compounds with trace concentration in this contribution. First, the response mechanism was characterized using the classical perturbational approach. Optimal sensitive film thickness and operation frequency are determined theoretically to achieve a relative linear characteristic response and a high gas sensitivity. Next, to improve of the corrosion resistance and frequency response characteristics of the sensor chip, Al/Au electrodes are used to form the resonator acted as the feedback element for oscillator. In addition, the substantial improvement is obtained in frequency stability of the resonator–oscillator referring to phase modulation approach. The measured short-term frequency stability of the oscillator at the operation frequency of 300 MHz is up to 2 Hz/s. The theoretical predictions are confirmed by the measured responses from the BSP3-coated SAW sensor for dimethylmethylphosphonate (DMMP) detection. Excellent threshold detection limit less than 0.004 mg/ $\text{m}^{3}$ and good sensitivity ( $\sim 3.09$ kHz/mg/ $\text{m}^{3})$ were achieved from the developed BSP3-coated SAW chemical sensor in the DMMP detection.

Selective Surface Acoustic Wave-Based Organophosphorus Sensor Employing a Host-Guest Self-Assembly Monolayer of β-Cyclodextrin Derivative.

Self-assembly and molecular imprinting technologies are very attractive technologies for the development of artificial recognition systems and provide chemical recognition based on need and not happenstance. In this paper, we employed a β-cyclodextrin derivative surface acoustic wave (SAW) chemical sensor for detecting the chemical warfare agents (CWAs) sarin (O-Isoprophyl methylphosphonofluoridate, GB). Using sarin acid (isoprophyl hydrogen methylphosphonate) as an imprinting template, mono[6-deoxy-6-[(mercaptodecamethylene)thio]]-β-cyclodextrin was prepared by self-assembled method on one of the SAW oscillators. After templates’ removal, a sensitive and selective molecular imprinting (MIP) monolayer for GB was prepared. Electrochemical impedance spectroscopy and atomic force microscope (AFM) were used to characterize this film. Comparing the detection results to GB by MIP film and non-MIP film, the molecularly imprinting effect was also proved. The resulting SAW sensor could detect sarin as low as 0.10 mg/m3 at room temperature and the frequency shift was about 300 Hz. The response frequency increased linearly with increasing sarin concentration in the range of 0.7 mg/m3~3.0 mg/m3. When sarin was detected under different temperatures, the SAW sensor exhibited outstanding sensitivity and reliability.

Application of Thin Metal Oxide Films in Acoustic Wave Chemical Sensors

Acoustic wave chemical sensors have several features such as high resolution and sensitivity, fast responserecovery time, superb overall stability and high dynamic range, which determine their appropriateness for gas analyte detection. The usability of acoustic sensors requires specific knowledge relating to the sensing mechanism, the properties of different acoustic wave modes and the criteria for selection of sensitive layers, involved in a wide range of gas-phase applications. This paper reports the most commonly used metal oxide film coated acoustic wave sensors, as well as their operation principle and practical application. Several advantages and disadvantages of each particular acoustic wave device are identified and the selectivity of the sensors is presented and discussed.

Real-time detection of styrene using SAW sensors based on hexafluoroisopropanol group functionalized hydrogen-bond acidic polymers

Hydrogen-bond acidic (HBA) polymers are well-established adsorbents for organophosphorus compounds and nitroaromatic explosives detection. In this paper, we report two HBA polymers for detection of styrene vapors based on 434-MHz surface acoustic wave (SAW) chemical sensors. These polymers, dubbed PLF and LSFA, are pendent hexafluoroisopropanol (HFIP)-group modified polysiloxanes, which were synthesized by one-step hydrosilylation reaction. Real-time response studies of these two sensors showed that they are highly sensitive to styrene vapors with excellent selectivity. After exposure to 5mg/m3 styrene vapor, the frequency shifts of the PLF and LSFA sensors have increased by 6.3kHz and 3.2kHz, respectively. The polymers are 20-fold less sensitive to toluene than to styrene while they have comparable sensitivity to 1-butene. In situ infrared spectroscopy studies demonstrated that the polymer–styrene interaction is attributed to the OH/π hydrogen bond between HFIP groups of the polymers and the ethylene group of styrene molecules.

The Respond Characteristic Property in Different Temperatures of SAW Sensor with p-tertbutylcalix[4]arene Coatings to Detect DMMP

This paper presents new effective approachs for the supermolecule film deposition of surface acoustic wave (SAW) chemical sensors for detecting DMMP. 25-(thioalkyl-alkoxy)-p-tertbutylcalix [4] arene self-assembly molecular imprinted film as the sensitive film was coated on the gold delay line of SAW sensors to detect DMMP. The sensor has special response to organoosphorus compounds and the respond characteristic property in different temperatures of SAW sensor was studied in detail, had important reference value in counter-terrorism.

A SAW-based chemical sensor for detecting sulfur-containing organophosphorus compounds using a two-step self-assembly and molecular imprinting technology.

This paper presents a new effective approach for the sensitive film deposition of surface acoustic wave (SAW) chemical sensors for detecting organophosphorus compounds such as O-ethyl-S-2-diisopropylaminoethyl methylphosphonothiolate (VX) containing sulfur at extremely low concentrations. To improve the adsorptive efficiency, a two-step technology is proposed for the sensitive film preparation on the SAW delay line utilizing gold electrodes. First, mono[6-deoxy-6-[(mercaptodecamethylene)thio]]-β-cyclodextrin is chosen as the sensitive material for VX detection, and a ∼2 nm-thick monolayer is formed on the SAW delay line by the binding of Au-S. This material is then analyzed by atomic force microscopy (AFM). Second, the VX molecule is used as the template for molecular imprinting. The template is then removed by washing the delay line with ethanol and distilled water, thereby producing the sensitive and selective material for VX detection. The performance of the developed SAW sensor is evaluated, and results show high sensitivity, low detection limit, and good linearity within the VX concentration of 0.15–5.8 mg/m3. The possible interactions between the film and VX are further discussed.

Some Observations on the Challenges of Chemical Sensor Commercialization

Chemical sensors continue to offer significant commercialization potential. They are an enabling technology of the ever-expanding digital world that seeks to measure (and control) our environment, our health and our manufacturing processes. The development and commercialization of chemical sensors has always been much more challenging than the development of physical sensors due to the vast number of potential measurands, the complexity of potential interferences and the (comparatively) low production volumes that existing markets will support.This talk is aimed at aspiring entrepreneurs and will use the development of some Surface Acoustic Wave (SAW) chemical sensor products as a case history. Particular attention will be given to detailing the chronology and issues encountered in the following steps:• initial invention and establishing the limits of the technology• identifying suitable niche applications• product development & system engineering• validation and agency approvals• production• marketing, sales and servicingCommercially successful products can result when the initial customer needs are deeply understood, the sensor performance exceeds market expectations, the time-to-market (and associated capital requirement) is correctly predicted and the market-acceptable selling price of the sensor is high enough to support the cost of production.

Modelling of chemical surface acoustic wave sensors and comparative analysis of new sensing materials

SUMMARY Comparative analysis of different, new gas sensing materials in surface acoustic wave chemical sensors is presented. Different gas sensing materials as polyaniline (PANI), Teflon AF 2400, polyisobutylene (PIB), polyepichlorohydrin (PECH) are considered. They are chosen according to the type of gas to be detected and the desired accuracy: Teflon AF 2400 thin film for the detection of CO2, PANI nanocomposites film that belongs to the group of conductive polymers for the detection of CO, NO2 and phosgene (COCl2), and PECH and PIB for the detection of dichloromethane (CH2Cl2, DCM). In the analysis, the simple and useful method of the complete analyses of gas chemical sensors is used. The method is based on the electrical equivalent circuit of the surface acoustic wave sensor. The method is very efficient and can be used for the optimal design of CO2 sensors. The results are compared with those presented in public literature and good agreement is obtained, demonstrating the validity of modelling. Copyright © 2012 John Wiley & Sons, Ltd.

Study on the Surface Acoustic Wave Sensor with Self-Assembly Imprinted Film of Calixarene Derivatives to Detect Organophosphorus Compounds

The molecularly imprinted technology and the self-assembly technique were used together on the calixarene surface acoustic wave (SAW) chemical sensors to detect organophosphorus compounds. 25-(thioalkyl-alkoxy)-p-tertbutylcalix[4] arene with self-assembled monolayer character was the sensitive coating of the sensors. The sensors had a special response to organophosphorus compounds and the response frequency shift of this sensor to organophosphorus compounds in 0.1 mg/m3 was 350 Hz. The response frequency increased linearly with the increase of the concentration of DMMP in the range from 0.1 to 0.6 mg/m3. The possible explanation of the interaction between the coatings and organophosphorus compounds was discussed.

English

The paper presents a new approach to surface acoustic wave (SAW) chemical sensor array design and data processing for recognition of volatile organic compounds (VOCs) based on transient responses. The array is constructed of variable thickness single polymer-coated SAW oscillator sensors. The thickness of polymer coatings are selected such that during the sensing period, different sensors are loaded with varied levels of diffusive inflow of vapour species due to different stages of termination of equilibration process. Using a single polymer for coating the individual sensors with different thickness introduces vapour-specific kinetics variability in transient responses. The transient shapes are analysed by wavelet decomposition based on Daubechies mother wavelets. The set of discrete wavelet transform (DWT) approximation coefficients across the array transients is taken to represent the vapour sample in two alternate ways. In one, the sets generated by all the transients are combined into a single set to give a single representation to the vapour. In the other, the set of approximation coefficients at each data point generated by all transients is taken to represent the vapour. The latter results in as many alternate representations as there are approximation coefficients. The alternate representations of a vapour sample are treated as different instances or realisations for further processing. The wavelet analysis is then followed by the principal component analysis (PCA) to create new feature space. A comparative analysis of the feature spaces created by both the methods leads to the conclusion that both methods yield complimentary information: the one reveals intrinsic data variables, and the other enhances class separability. The present approach is validated by generating synthetic transient response data based on a prototype polyisobutylene (PIB) coated 3-element SAW sensor array exposed to 7 VOC vapours: chloroform, chlorobenzene o-dichlorobenzene, n-heptane, toluene, n-hexane and n-octane. Defence Science Journal, 2010, 60(4), pp.377-386 , DOI:http://dx.doi.org/10.14429/dsj.60.494

Mass sensitivity analysis and designing of surface acoustic wave resonators for chemical sensors

The sensitivity of surface acoustic wave (SAW) chemical sensors depends on several factors such as the frequency and phase point of SAW device operation, sensitivity of the SAW velocity to surface mass loading, sensitivity of the SAW oscillator resonance to the loop phase shift, film thickness and oscillator electronics. This paper analyzes the influence of the phase point of operation in SAW oscillator sensors based on two-port resonator devices. It is found that the mass sensitivity will be enhanced if the SAW device has a nonlinear dependence on the frequency (delay ∼ frequency−1). This requires the device to generate and operate in a ωτg(ω) = const region in the device passband, where ω denotes the angular frequency of oscillation and τg(ω) denotes the phase slope of the SAW resonator device. A SAW coupled resonator filter (CRF) that take advantage of mode coupling is considered in realizing such a device to help in shaping the phase transfer characteristics of a high mass sensitivity sensor. The device design and simulation results are presented within the coupling-of-modes formalism.

High frequency SAW stabilized oscillators for chemical agents sensors

The surface acoustic wave (SAW) chemical agents sensors usually operate in the oscillator feed-back configuration. It converts a molecular interactions between SAW surface and chemisensitive layer placed on it to relative easy to measurement electrical quantities (most often it is an operating frequency or phase change). Although in the SAW sensors the key role play chemisensitive coatings but nearly as important as the coatings are electronic circuits cooperating with SAW devices. The results of theoretical calculations show that the SAW sensors operating frequency increasing is profitable from the sensitivity point of view. Unfortunately, an advantageous sensitivity-frequency dependence is hard to apply because of decreasing of SAW device dimensions and thereby the area of the chemisensitive layer with the operating frequency. The smaller area of the layer, the smaller amount of detecting gas particles sorbed and the weakest response of the sensor. It is possible to avoid the problem using special constructions of SAW stabilised oscillators. In the paper such constructions have been described.

A novel wireless, passive CO2 sensor incorporating a surface acoustic wave reflective delay line

A 440 MHz wireless and passive surface acoustic wave (SAW) chemical sensor was developed forCO2 detection. The developed SAW gas sensor is composed of single phaseunidirectional transducers (SPUDTs), three shorted grating reflectors, andCO2-sensitivepolymer film on 41° YX LiNbO3 substrate. Coupling of modes (COM) modeling was used to find optimal designparameters. Using the extracted design parameters, the SAW device wasfabricated. Teflon AF 2400 was used as the sensitive film because it provides highCO2 solubility, permeability and selectivity. In wireless device testing using anetwork analyzer, four sharp reflection peaks with high signal-to-noise(S/N) ratio, small signal attenuation, and few spurious peaks were observedin the time domain. The time positions of the reflection peaks werewell matched with the predicted values from the simulation. Infusion ofCO2 into thechamber induced large phase shifts of the reflection peaks. Good linearity and repeatability were observedfor a CO2 concentration of 0–450 ppm. The obtained sensitivity was1.98° ppm−1. Temperature and humidity effects were also investigated during the sensitivity evaluationprocess.

Improving the stability of surface acoustic wave (SAW) chemical sensor coatings using photopolymerization

Submicron particles of a diethyl ester of p-phenylenediacrylic acid (EPA) were produced by the technique known as rapid expansion of supercritical solutions (RESS) and were deposited onto surface acoustic wave (SAW) resonators. The EPA particles were polymerized in the solid-state directly on the surface of the SAW devices in order to stabilize the mechanical properties of the sensor coatings. The sensor affinity to particular vapors was enhanced by performing the polymerization step in the presence of organic template vapors. The resulting SAW sensors exhibited high quality factors ( Q 0) and we have demonstrated the sensor stability for periods up to 3.8 years.

Design of ST-cut quartz surface acoustic wave chemical sensors

This research investigates the design rules polymer-based ST-cut quartz surface acoustic wave (SAW) sensors used in detecting organophosphorous compounds. A complex shear modulus is used to represent express different types of polymer (glassy, glassy–rubbery, and rubbery). Different propagation directions lead to different wave propagation properties in SAW devices, such as attenuation and velocity. Hence, the choice of polymer type and wave propagation direction is a very important aspect of sensor design. Calculations indicate that the glassy–rubbery and rubbery film coated on SAW sensors very sensitively detect organophosphorous vapor. However, the glassy–rubbery film is most suitable in sensing applications, because it makes signal attenuation significantly. Although sensitivity is high when an acoustic wave propagates in the Y-direction, the X-direction is preferred at the optimum path on account of the excellent temperature stability in the X-propagation direction. Therefore, SAW vapor sensors with an appropriate chemical interface and wave propagation direction are designed to yield superior performance.

Chemical Vapor Deposition by Pulsed Ultrasonic Direct Injection of Liquid Precursors Produces Versatile Method for Creation of Thin Film Circuits and Devices.

ABSTRACTWe demonstrate a unique, ultrasonic direct injection method that employs nanophase materials (e.g. polymers, metal-organic and ceramic precursors). By use ofin situprocess control, and modification of process parameters, morphology, and structure may be varied to produce desired characteristics. By sequential application of these strategies one may fabricate MEMS, OLED's, deposit conformal coatings, create surface acoustic wave (SAW) chemical sensors, and many other thin film circuits and devices.

Acoustic Wave Chemical Sensors for Gases

A great number of publications devoted to the physicochemical principles of the operation of acoustic wave chemical sensors for gases, the state of the art, and the prospects for further development were surveyed and analyzed.

The “NRL-SAWRHINO”: a nose for toxic gases

At the Naval Research Laboratory (NRL), surface acoustic wave (SAW) chemical sensor systems have been in development since 1981. The primary focus has been the detection and identification of chemical agents and other toxic gases or vapors. In the recently developed “NRL-SAWRHINO” system (Rhino, Gr. Nose), a self-contained unit has been developed capable of autonomous field operation. An automated dual gas sampling system is included, for immediate and periodic detection capability. The latter, utilizes a trap-and-purge miniature gas chromatographic column, which serves to collect, concentrate, and separate vapor or gas mixtures prior to SAW analysis. The SAWRHINO includes all the necessary electronic and microprocessor control, SAW sensor temperature control, onboard neural net pattern recognition capability, and visual/audible alarm features for field deployment. The SAWRHINO has been trained to detect and identify a range of nerve and blister agents, and related simulants, and to discriminate against a wide range of interferent vapors and gases.