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Film Bulk Acoustic Wave Resonator for Trace Chemical Warfare Agents Simulants Detection in Micro Chromatography
... Over the last two decades, there has been an increased interest in developing and producing high-frequency devices (from sub-GHz to tens of GHz range) such as bulk acoustic waves (BAWs) resonators which have been used as filters [231][232][233][234][235][236], duplexers [237][238][239], multiplexers [240,241], gas sensors [242][243][244][245], and chemical biosensors [71,246,247]. The film bulk acoustic wave devices are one of the BAW resonators which consisted of a piezoelectric layer usually zinc oxide (ZnO), aluminum nitride (AIN), or lead zirconate titanate (PZT) sandwiched between two metal electrodes to which microwave (RF) signal is applied [245]. ...
Piezoelectric microelectromechanical system (piezo-MEMS)-based mass sensors including the piezoelectric microcantilevers, surface acoustic waves (SAW), quartz crystal microbalance (QCM), piezoelectric micromachined ultrasonic transducer (PMUT), and film bulk acoustic wave resonators (FBAR) are highlighted as suitable candidates for highly sensitive gas detection application. This paper presents the piezo-MEMS gas sensors' characteristics such as their miniaturized structure, the capability of integration with readout circuit, and fabrication feasibility using multiuser technologies. The development of the piezoelectric MEMS gas sensors is investigated for the application of low-level concentration gas molecules detection. In this work, the various types of gas sensors based on piezoelectricity are investigated extensively including their operating principle, besides their material parameters as well as the critical design parameters, the device structures, and their sensing materials including the polymers, carbon, metal-organic framework, and graphene.
... The polymer PEI was chosen as the coating material in the sensor since this polymer is commercially available and capable of providing hydrogen bonding by large numbers of imine groups. In addition, our preliminary results have shown that it could be a potential candidate as sensitive materials for the detection of chemical warfare agents [40]. The response here is defined as the maximum response of the analyte. ...
A microfluidic film bulk acoustic wave resonator gas sensor (mFBAR) adapted specifically as an in-line detector in gas chromatography was described. This miniaturized vapor sensor was a non-destructive detector with very low dead volume (0.02 μL). It was prepared by enclosing the resonator in a microfluidic channel on a chip with dimensions of only 15 mm × 15 mm × 1 mm. The device with polymer coating showed satisfactory performance in the detection of organophosphorus compound, demonstrating a very low detection limit (a dozen parts per billion) with relatively short response time (about fifteen seconds) toward the simulant of chemical warfare agent, dimethyl methylphosphonate. The in-line detection of the mFBAR sensor with FID was constructed and employed to directly measure the concentration profile on the solid surface by the mFBAR with the controlled concentration profile in the mobile phase at the same time. The difference of peak-maximum position between mobile phase and solid phase could be a convenient indicator to measure mass transfer rate. With the response of the mFBAR and FID obtained in one injection, an injection mass-independent parameter can be calculated and used to identify the analyte of interest.
An important field of research is the miniaturization of analytical systems for laboratory applications and on-field analysis. In particular, gas chromatography (GC) has benefited from the recent advances in enabling technologies like photolithography, micromachining, hot embossing, and 3D-printing to improve sampling and sample preparation, microcolumn technologies, and detection. In this article, the developments and applications reported since 2015 were reviewed and summarized. Important applications using benchtop instruments, portable GCs, and micro-GCs (µGCs) were showcased to illustrate the current challenges associated with each miniaturized interfaces and systems. For instance, portable instruments need to be energy-efficient and ideally depend on renewable sources for carrier gas generation. Lastly, multidimensional separations were addressed using miniaturized systems to effectively improve the peak capacity of portable systems.
Gravimetric resonators based on Micro/Nanoelectromechanical System (M/NEMS) are potential candidates in developing smaller, less expensive, and higher performance gas sensors. Metal organic frameworks (MOFs), with high surface areas, recently come into focus as advanced nano-porous sensitive materials in micro gravimetric gas sensors. The surface of MOFs on those sensors is critical in offering water stability and varying absorption behaviors. However, the influences of surface on sensing performance are less explored and the strategy to tune surface properties of MOFs mounted on gravimetric resonators is still rare. In this paper, a straightforward strategy to engineer surface properties of MOFs, specifically Cu3(benzenetricarboxylate)2 (known as HKUST-1), is reported and the surface hydrophilicity/hydrophobicity of HKUST-1 is tuned by chemical vapor deposition combined with monolayer self-assembly. It is found out that the hybrid inorganic and organic surface engineering strategy not only preserves the absorption capacity of inner MOFs but also significantly enhances sensor stability toward water.
In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group's properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.
A vapor sensor comprising a nanoparticle-coated microfabricated optofluidic ring resonator (µOFRR) is introduced. A multilayer film of polyether functionalized thiolate monolayer protected gold nanoparticles (MPN) was solvent cast on the inner wall of the hollow cylindrical SiOx µOFRR resonator structure, and whispering gallery mode (WGM) resonances were generated with a 1550-nm tunable laser via an optical fiber taper. Reversible shifts in the WGM resonant wavelength upon vapor exposure were detected with a photodetector. The μOFRR chip was connected to a pair of upstream etched-Si chips containing PDMS-coated separation μcolumns and calibration curves were generated from the peak-area responses to five volatile organic compounds (VOCs). Calibration curves were linear, and the sensitivities reflected the influence of analyte volatility and analyte-MPN functional group affinity. Sorption-induced changes in film thickness apparently dominate over changes in the refractive index of the film as the determinant of responses for all VOCs. Peaks from the MPN-coated µOFRR were just 20-50% wider than those from a flame ionization detector for similar μcolumn separation conditions, reflecting the rapid response of the sensor for VOCs. The five VOCs were baseline separated in < 1.67 min, with detection limits as low as 38 ng.
A ready-to-deploy implementation of a microfabricated gas chromatography (μGC) system characterized for detecting hazardous air pollutants (HAPs) at parts-per-billion (ppb) concentrations in complex mixtures has been described. A microfabricated preconcentrator (μPC), MEMS separation column with on-chip thermal conductivity detector (μSC-TCD), flow controller unit, and all necessary flow and thermal management as well as user interface circuitry are integrated to realize a fully functional μGC system. The work reports extensive characterization of μPC and μSC-TCD for target analytes: benzene, toluene, tetrachloroethylene, chlorobenzene, ethylbenzene, and p-xylene. A Limit of Detection (LOD) of ∼1 ng was achieved, which corresponds to a sampling time of 10 min at a flow rate of 1 mL/min for an analyte present at ∼25 ppbv. An innovative method using flow-manipulation generated sharp injection plugs from the μPC even in the presence of a flow-sensitive detector like a μTCD. The μGC system is compared against conventional automated thermal desorption–gas chromatography–flame ionization detector (ATD–GC–FID) system for real gasoline samples in simulated car refueling scenario. The μGC system detected five peaks, including three of the target analytes and required ∼3 orders of magnitude lower sample volume as compared to the conventional system.
Although digital microfluidics has shown great potential in a wide range of applications, a lab-on-a-chip with integrated digital droplet actuators and powerful biochemical sensors is still lacking. To address the demand, a fully integrated chip with electrowetting-on-dielectric (EWOD) and a film bulk acoustic resonator (FBAR) sensor is introduced, where an EWOD actuator manipulates digital droplets and the FBAR sensor detects the presence of substances in the droplets, respectively. The piezoelectric layer of the FBAR sensor and the dielectric layer of the EWOD share the same aluminum nitride (AlN) thin film, which is a key factor to achieve the full integration of the two completely different devices. The liquid droplets are reliably managed by the EWOD actuator to sit on or move off the FBAR sensor precisely. Sessile drop experiments and limit of detection (LOD) experiments are carried out to characterize the EWOD actuator and the FBAR sensor, respectively. Taking advantage of the digital droplet operation, a ‘dry sensing mode’ of the FBAR sensor in the lab-on-a-chip microsystem is proposed, which has a much higher signal to noise ratio than the conventional ‘wet sensing mode’. Hg2+ droplets with various concentrations are transported and sensed to demonstrate the capability of the integrated system. The EWOD–FBAR chip is expected to play an important role in many complex lab-on-a-chip applications.
Micro gas chromatography (μGC) has been continuously gaining attention since the last century owing to multiple favorable characteristics, such as its small size, low power consumption and minimal production and maintenance costs. μGC has the potential to provide practical solutions to emerging analytical challenges in security, health, and environment. In this review, we summarize recent advances in micro detectors for μGC, including the study of the miniaturization of conventional detectors and the development of novel detectors for μGC chromatography.
This paper reports a novel miniaturized detector for gas chromatography based on film bulk acoustic resonator (FBAR) sensor array. Polymer coated FBAR demonstrated detection limit of parts per million (ppm) concentrations for several volatile organic vapors. Orthogonal selectivity between n-pentane and acetone is achieved by integrating different polymer coated FBARs as sensor array. A prototype of chromatographic instrument using FBAR sensor array as detector was demonstrated by facile hyphenation of the device with commercial separation column. Such GC system is used to quantitative identification of dual gas mixture by employing principal component analysis (PCA). This MEMS chemical sensor technology offers high sensing performance, miniaturized size, and low power consumption, which are critical for development of portable gas chromatography.
A Love-wave device with graphene oxide (GO) as sensitive layer has been developed for the detection of chemical warfare agent (CWA) simulants. Sensitive films were fabricated by airbrushing GO dispersions onto Love-wave devices. The resulting Love-wave sensors detected very low CWA simulant concentrations in synthetic air at room temperature (as low as 0.2 ppm for dimethyl-methylphosphonate, DMMP, a simulant of sarin nerve gas, and 0.75 ppm for dipropylene glycol monomethyl ether, DPGME, a simulant of nitrogen mustard). High responses to DMMP and DPGME were obtained with sensitivities of 3087 and 760 Hz/ppm respectively. Very low limit of detection (LOD) values (9 and 40 ppb for DMMP and DPGME, respectively) were calculated from the achieved experimental data. The sensor exhibited outstanding sensitivity, good linearity and repeatability to all simulants tested. The detection mechanism is here explained in terms of hydrogen bonding formation between the tested CWA simulants and GO.
With the help of micro-electromechanical systems (MEMS) and complementary metal-oxide-semiconductor (CMOS) technology, a portable micro gas chromatography ([Formula: see text]) system for lung cancer associated volatile organic compounds (VOCs) detection is realized for the first time. The system is composed of an MEMS preconcentrator, an MEMS separation column, and a CMOS system-on-chip (SoC). The preconcentrator provides a concentration ratio of 2170. The separation column can separate more than seven types of lung cancer associated VOCs. The SoC is fabricated by a TSMC [Formula: see text] 2P4M process including the CMOS VOCs detector, sensor calibration circuit, low-noise chopper instrumentation amplifier (IA), 10 bit analog to digital converter, and the microcontrol unit (MCU). Experimental results show that the system is able to detect seven types of lung cancer associated VOCs (acetone, 2-butanone, benzene, heptane, toluene, m-xylene, 1,3,5-trimethylbenzene). The concentration linearity is [Formula: see text] and the detection sensitivity is up to 15 ppb with 1,3,5-trimethylbenzene.
The flexural plate wave device is capable of sensing transition behaviors of homogeneous amorphous polymers applied as thin films to its surface. The changes in polymer properties at the static glass transition temperature are sensed as a change in slope of the frequency-temperature plot. Frequency-dependent relaxation properties are detected with a sigmoidal change in slope of the frequency-temperature plot and a minimum in signal amplitude. The transitions observed using poly(vinyl acetate), poly(tert-butyl acrylate), poly(isobutylene), and poly(vinyl propionate) are correlated with the properties of these polymers known by independent methods. The responses of the flexural plate wave device at 5 MHz are in accord with the results of conventional bulk-wave ultrasonic experiments at similar frequencies. The relevance of polymer transition processes to the performance of polymer-coated acoustic vapor sensors is discussed.
An E-nose based on surface acoustic wave (SAW) sensors has been developed, and sensitive polymer coatings have been optimized to detect simulants of chemical warfare agents (CWAs). The polymers selected have allowed to discriminate among simulants and classify them at low concentrations in air through Pattern Recognition Methods. Good detection responses have been achieved for very low concentrations, such as 0.05 ppm for Dimethyl methylphosphonate (DMMP) and 0.5 ppm for dipropylene glycol monomethyl ether (DPGME).
Miniaturized gas chromatography (GC) systems can provide fast, quantitative analysis of chemical vapors in an ultrasmall package. We describe a chemical sensor technology based on resonant nanoelectromechanical systems (NEMS) mass detectors that provides the speed, sensitivity, specificity, and size required by the microscale GC paradigm. Such NEMS sensors have demonstrated detection of subparts per billion (ppb) concentrations of a phosphonate analyte. By combining two channels of NEMS detection with an ultrafast GC front-end, chromatographic analysis of 13 chemicals was performed within a 5 s time window.